// Copyright 2014 The Servo Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

pub struct GlFns {
    ffi_gl_: GlFfi,
}

impl GlFns {
    pub unsafe fn load_with<'a, F>(loadfn: F) -> Rc<dyn Gl>
    where
        F: FnMut(&str) -> *const c_void,
    {
        let ffi_gl_ = GlFfi::load_with(loadfn);
        Rc::new(GlFns { ffi_gl_: ffi_gl_ }) as Rc<dyn Gl>
    }
}

impl Gl for GlFns {
    fn get_type(&self) -> GlType {
        GlType::Gl
    }

    fn buffer_data_untyped(
        &self,
        target: GLenum,
        size: GLsizeiptr,
        data: *const GLvoid,
        usage: GLenum,
    ) {
        unsafe {
            self.ffi_gl_.BufferData(target, size, data, usage);
        }
    }

    fn buffer_sub_data_untyped(
        &self,
        target: GLenum,
        offset: isize,
        size: GLsizeiptr,
        data: *const GLvoid,
    ) {
        unsafe {
            self.ffi_gl_.BufferSubData(target, offset, size, data);
        }
    }

    fn map_buffer(&self,
                  target: GLenum,
                  access: GLbitfield) -> *mut c_void {
        unsafe {
            return self.ffi_gl_.MapBuffer(target, access);
        }
    }

    fn map_buffer_range(&self,
                        target: GLenum,
                        offset: GLintptr,
                        length: GLsizeiptr,
                        access: GLbitfield) -> *mut c_void {
        unsafe {
            return self.ffi_gl_.MapBufferRange(target, offset, length, access);
        }
    }

    fn unmap_buffer(&self, target: GLenum) -> GLboolean {
        unsafe {
            return self.ffi_gl_.UnmapBuffer(target);
        }
    }

    fn shader_source(&self, shader: GLuint, strings: &[&[u8]]) {
        let pointers: Vec<*const u8> = strings.iter().map(|string| (*string).as_ptr()).collect();
        let lengths: Vec<GLint> = strings.iter().map(|string| string.len() as GLint).collect();
        unsafe {
            self.ffi_gl_.ShaderSource(
                shader,
                pointers.len() as GLsizei,
                pointers.as_ptr() as *const *const GLchar,
                lengths.as_ptr(),
            );
        }
        drop(lengths);
        drop(pointers);
    }

    fn tex_buffer(&self, target: GLenum, internal_format: GLenum, buffer: GLuint) {
        unsafe {
            self.ffi_gl_.TexBuffer(target, internal_format, buffer);
        }
    }

    fn read_buffer(&self, mode: GLenum) {
        unsafe {
            self.ffi_gl_.ReadBuffer(mode);
        }
    }

    fn read_pixels_into_buffer(
        &self,
        x: GLint,
        y: GLint,
        width: GLsizei,
        height: GLsizei,
        format: GLenum,
        pixel_type: GLenum,
        dst_buffer: &mut [u8],
    ) {
        // Assumes that the user properly allocated the size for dst_buffer.
        let mut row_length = 0;
        unsafe {
            self.ffi_gl_.GetIntegerv(ffi::PACK_ROW_LENGTH, &mut row_length as _);
        }
        if row_length == 0 {
            row_length = width;
        } else {
            assert!(row_length >= width);
        }
        assert_eq!(calculate_length(row_length, height, format, pixel_type), dst_buffer.len());

        unsafe {
            // We don't want any alignment padding on pixel rows.
            self.ffi_gl_.PixelStorei(ffi::PACK_ALIGNMENT, 1);
            self.ffi_gl_.ReadPixels(
                x,
                y,
                width,
                height,
                format,
                pixel_type,
                dst_buffer.as_mut_ptr() as *mut c_void,
            );
        }
    }

    fn read_pixels(
        &self,
        x: GLint,
        y: GLint,
        width: GLsizei,
        height: GLsizei,
        format: GLenum,
        pixel_type: GLenum,
    ) -> Vec<u8> {
        let len = calculate_length(width, height, format, pixel_type);
        let mut pixels: Vec<u8> = Vec::new();
        pixels.reserve(len);
        unsafe {
            pixels.set_len(len);
        }

        self.read_pixels_into_buffer(
            x,
            y,
            width,
            height,
            format,
            pixel_type,
            pixels.as_mut_slice(),
        );

        pixels
    }

    unsafe fn read_pixels_into_pbo(&self,
                            x: GLint,
                            y: GLint,
                            width: GLsizei,
                            height: GLsizei,
                            format: GLenum,
                            pixel_type: GLenum) {
        self.ffi_gl_.ReadPixels(x, y, width, height, format, pixel_type, ptr::null_mut());
    }

    fn sample_coverage(&self, value: GLclampf, invert: bool) {
        unsafe {
            self.ffi_gl_.SampleCoverage(value, invert as GLboolean);
        }
    }

    fn polygon_offset(&self, factor: GLfloat, units: GLfloat) {
        unsafe {
            self.ffi_gl_.PolygonOffset(factor, units);
        }
    }

    fn pixel_store_i(&self, name: GLenum, param: GLint) {
        unsafe {
            self.ffi_gl_.PixelStorei(name, param);
        }
    }

    fn gen_buffers(&self, n: GLsizei) -> Vec<GLuint> {
        let mut result = vec![0 as GLuint; n as usize];
        unsafe {
            self.ffi_gl_.GenBuffers(n, result.as_mut_ptr());
        }
        result
    }

    fn gen_renderbuffers(&self, n: GLsizei) -> Vec<GLuint> {
        let mut result = vec![0 as GLuint; n as usize];
        unsafe {
            self.ffi_gl_.GenRenderbuffers(n, result.as_mut_ptr());
        }
        result
    }

    fn gen_framebuffers(&self, n: GLsizei) -> Vec<GLuint> {
        let mut result = vec![0 as GLuint; n as usize];
        unsafe {
            self.ffi_gl_.GenFramebuffers(n, result.as_mut_ptr());
        }
        result
    }

    fn gen_textures(&self, n: GLsizei) -> Vec<GLuint> {
        let mut result = vec![0 as GLuint; n as usize];
        unsafe {
            self.ffi_gl_.GenTextures(n, result.as_mut_ptr());
        }
        result
    }

    fn gen_vertex_arrays(&self, n: GLsizei) -> Vec<GLuint> {
        let mut result = vec![0 as GLuint; n as usize];
        unsafe {
            self.ffi_gl_.GenVertexArrays(n, result.as_mut_ptr())
        }
        result
    }

    fn gen_vertex_arrays_apple(&self, n: GLsizei) -> Vec<GLuint> {
        let mut result = vec![0 as GLuint; n as usize];
        unsafe {
            self.ffi_gl_.GenVertexArraysAPPLE(n, result.as_mut_ptr())
        }
        result
    }

    fn gen_queries(&self, n: GLsizei) -> Vec<GLuint> {
        let mut result = vec![0 as GLuint; n as usize];
        unsafe {
            self.ffi_gl_.GenQueries(n, result.as_mut_ptr());
        }
        result
    }

    fn begin_query(&self, target: GLenum, id: GLuint) {
        unsafe {
            self.ffi_gl_.BeginQuery(target, id);
        }
    }

    fn end_query(&self, target: GLenum) {
        unsafe {
            self.ffi_gl_.EndQuery(target);
        }
    }

    fn query_counter(&self, id: GLuint, target: GLenum) {
        unsafe {
            self.ffi_gl_.QueryCounter(id, target);
        }
    }

    fn get_query_object_iv(&self, id: GLuint, pname: GLenum) -> i32 {
        let mut result = 0;
        unsafe {
            self.ffi_gl_.GetQueryObjectiv(id, pname, &mut result);
        }
        result
    }

    fn get_query_object_uiv(&self, id: GLuint, pname: GLenum) -> u32 {
        let mut result = 0;
        unsafe {
            self.ffi_gl_.GetQueryObjectuiv(id, pname, &mut result);
        }
        result
    }

    fn get_query_object_i64v(&self, id: GLuint, pname: GLenum) -> i64 {
        let mut result = 0;
        unsafe {
            self.ffi_gl_.GetQueryObjecti64v(id, pname, &mut result);
        }
        result
    }

    fn get_query_object_ui64v(&self, id: GLuint, pname: GLenum) -> u64 {
        let mut result = 0;
        unsafe {
            self.ffi_gl_.GetQueryObjectui64v(id, pname, &mut result);
        }
        result
    }

    fn delete_queries(&self, queries: &[GLuint]) {
        unsafe {
            self.ffi_gl_
                .DeleteQueries(queries.len() as GLsizei, queries.as_ptr());
        }
    }

    fn delete_vertex_arrays(&self, vertex_arrays: &[GLuint]) {
        unsafe {
            self.ffi_gl_
                .DeleteVertexArrays(vertex_arrays.len() as GLsizei, vertex_arrays.as_ptr());
        }
    }

    fn delete_vertex_arrays_apple(&self, vertex_arrays: &[GLuint]) {
        unsafe {
            self.ffi_gl_
                .DeleteVertexArraysAPPLE(vertex_arrays.len() as GLsizei, vertex_arrays.as_ptr());
        }
    }

    fn delete_buffers(&self, buffers: &[GLuint]) {
        unsafe {
            self.ffi_gl_
                .DeleteBuffers(buffers.len() as GLsizei, buffers.as_ptr());
        }
    }

    fn delete_renderbuffers(&self, renderbuffers: &[GLuint]) {
        unsafe {
            self.ffi_gl_
                .DeleteRenderbuffers(renderbuffers.len() as GLsizei, renderbuffers.as_ptr());
        }
    }

    fn delete_framebuffers(&self, framebuffers: &[GLuint]) {
        unsafe {
            self.ffi_gl_
                .DeleteFramebuffers(framebuffers.len() as GLsizei, framebuffers.as_ptr());
        }
    }

    fn delete_textures(&self, textures: &[GLuint]) {
        unsafe {
            self.ffi_gl_
                .DeleteTextures(textures.len() as GLsizei, textures.as_ptr());
        }
    }

    fn framebuffer_renderbuffer(
        &self,
        target: GLenum,
        attachment: GLenum,
        renderbuffertarget: GLenum,
        renderbuffer: GLuint,
    ) {
        unsafe {
            self.ffi_gl_.FramebufferRenderbuffer(
                target,
                attachment,
                renderbuffertarget,
                renderbuffer,
            );
        }
    }

    fn renderbuffer_storage(
        &self,
        target: GLenum,
        internalformat: GLenum,
        width: GLsizei,
        height: GLsizei,
    ) {
        unsafe {
            self.ffi_gl_
                .RenderbufferStorage(target, internalformat, width, height);
        }
    }

    fn depth_func(&self, func: GLenum) {
        unsafe {
            self.ffi_gl_.DepthFunc(func);
        }
    }

    fn active_texture(&self, texture: GLenum) {
        unsafe {
            self.ffi_gl_.ActiveTexture(texture);
        }
    }

    fn attach_shader(&self, program: GLuint, shader: GLuint) {
        unsafe {
            self.ffi_gl_.AttachShader(program, shader);
        }
    }

    fn bind_attrib_location(&self, program: GLuint, index: GLuint, name: &str) {
        let c_string = CString::new(name).unwrap();
        unsafe {
            self.ffi_gl_
                .BindAttribLocation(program, index, c_string.as_ptr())
        }
    }

    // https://www.khronos.org/registry/OpenGL-Refpages/es2.0/xhtml/glGetUniform.xml
    unsafe fn get_uniform_iv(&self, program: GLuint, location: GLint, result: &mut [GLint]) {
        assert!(!result.is_empty());
        self.ffi_gl_
            .GetUniformiv(program, location, result.as_mut_ptr());
    }

    // https://www.khronos.org/registry/OpenGL-Refpages/es2.0/xhtml/glGetUniform.xml
    unsafe fn get_uniform_fv(&self, program: GLuint, location: GLint, result: &mut [GLfloat]) {
        assert!(!result.is_empty());
        self.ffi_gl_
            .GetUniformfv(program, location, result.as_mut_ptr());
    }

    fn get_uniform_block_index(&self, program: GLuint, name: &str) -> GLuint {
        let c_string = CString::new(name).unwrap();
        unsafe {
            self.ffi_gl_
                .GetUniformBlockIndex(program, c_string.as_ptr())
        }
    }

    fn get_uniform_indices(&self, program: GLuint, names: &[&str]) -> Vec<GLuint> {
        let c_strings: Vec<CString> = names.iter().map(|n| CString::new(*n).unwrap()).collect();
        let pointers: Vec<*const GLchar> = c_strings.iter().map(|string| string.as_ptr()).collect();
        let mut result = Vec::with_capacity(c_strings.len());
        unsafe {
            result.set_len(c_strings.len());
            self.ffi_gl_.GetUniformIndices(
                program,
                pointers.len() as GLsizei,
                pointers.as_ptr(),
                result.as_mut_ptr(),
            );
        }
        result
    }

    fn bind_buffer_base(&self, target: GLenum, index: GLuint, buffer: GLuint) {
        unsafe {
            self.ffi_gl_.BindBufferBase(target, index, buffer);
        }
    }

    fn bind_buffer_range(
        &self,
        target: GLenum,
        index: GLuint,
        buffer: GLuint,
        offset: GLintptr,
        size: GLsizeiptr,
    ) {
        unsafe {
            self.ffi_gl_
                .BindBufferRange(target, index, buffer, offset, size);
        }
    }

    fn uniform_block_binding(
        &self,
        program: GLuint,
        uniform_block_index: GLuint,
        uniform_block_binding: GLuint,
    ) {
        unsafe {
            self.ffi_gl_
                .UniformBlockBinding(program, uniform_block_index, uniform_block_binding);
        }
    }

    fn bind_buffer(&self, target: GLenum, buffer: GLuint) {
        unsafe {
            self.ffi_gl_.BindBuffer(target, buffer);
        }
    }

    fn bind_vertex_array(&self, vao: GLuint) {
        unsafe {
            self.ffi_gl_.BindVertexArray(vao);
        }
    }

    fn bind_vertex_array_apple(&self, vao: GLuint) {
        unsafe {
            self.ffi_gl_.BindVertexArrayAPPLE(vao)
        }
    }

    fn bind_renderbuffer(&self, target: GLenum, renderbuffer: GLuint) {
        unsafe {
            self.ffi_gl_.BindRenderbuffer(target, renderbuffer);
        }
    }

    fn bind_framebuffer(&self, target: GLenum, framebuffer: GLuint) {
        unsafe {
            self.ffi_gl_.BindFramebuffer(target, framebuffer);
        }
    }

    fn bind_texture(&self, target: GLenum, texture: GLuint) {
        unsafe {
            self.ffi_gl_.BindTexture(target, texture);
        }
    }

    fn bind_vertex_buffer(&self, binding_index: GLuint, buffer: GLuint, offset: GLintptr, stride: GLint) {
        unsafe { self.ffi_gl_.BindVertexBuffer(binding_index, buffer, offset, stride) }
    }

    fn draw_buffers(&self, bufs: &[GLenum]) {
        unsafe {
            self.ffi_gl_
                .DrawBuffers(bufs.len() as GLsizei, bufs.as_ptr());
        }
    }

    // FIXME: Does not verify buffer size -- unsafe!
    fn tex_image_2d(
        &self,
        target: GLenum,
        level: GLint,
        internal_format: GLint,
        width: GLsizei,
        height: GLsizei,
        border: GLint,
        format: GLenum,
        ty: GLenum,
        opt_data: Option<&[u8]>,
    ) {
        match opt_data {
            Some(data) => unsafe {
                self.ffi_gl_.TexImage2D(
                    target,
                    level,
                    internal_format,
                    width,
                    height,
                    border,
                    format,
                    ty,
                    data.as_ptr() as *const GLvoid,
                );
            },
            None => unsafe {
                self.ffi_gl_.TexImage2D(
                    target,
                    level,
                    internal_format,
                    width,
                    height,
                    border,
                    format,
                    ty,
                    ptr::null(),
                );
            },
        }
    }

    fn compressed_tex_image_2d(
        &self,
        target: GLenum,
        level: GLint,
        internal_format: GLenum,
        width: GLsizei,
        height: GLsizei,
        border: GLint,
        data: &[u8],
    ) {
        unsafe {
            self.ffi_gl_.CompressedTexImage2D(
                target,
                level,
                internal_format,
                width,
                height,
                border,
                data.len() as GLsizei,
                data.as_ptr() as *const GLvoid,
            );
        }
    }

    fn compressed_tex_sub_image_2d(
        &self,
        target: GLenum,
        level: GLint,
        xoffset: GLint,
        yoffset: GLint,
        width: GLsizei,
        height: GLsizei,
        format: GLenum,
        data: &[u8],
    ) {
        unsafe {
            self.ffi_gl_.CompressedTexSubImage2D(
                target,
                level,
                xoffset,
                yoffset,
                width,
                height,
                format,
                data.len() as GLsizei,
                data.as_ptr() as *const GLvoid,
            );
        }
    }

    // FIXME: Does not verify buffer size -- unsafe!
    fn tex_image_3d(
        &self,
        target: GLenum,
        level: GLint,
        internal_format: GLint,
        width: GLsizei,
        height: GLsizei,
        depth: GLsizei,
        border: GLint,
        format: GLenum,
        ty: GLenum,
        opt_data: Option<&[u8]>,
    ) {
        unsafe {
            let pdata = match opt_data {
                Some(data) => mem::transmute(data.as_ptr()),
                None => ptr::null(),
            };
            self.ffi_gl_.TexImage3D(
                target,
                level,
                internal_format,
                width,
                height,
                depth,
                border,
                format,
                ty,
                pdata,
            );
        }
    }

    fn copy_tex_image_2d(
        &self,
        target: GLenum,
        level: GLint,
        internal_format: GLenum,
        x: GLint,
        y: GLint,
        width: GLsizei,
        height: GLsizei,
        border: GLint,
    ) {
        unsafe {
            self.ffi_gl_.CopyTexImage2D(
                target,
                level,
                internal_format,
                x,
                y,
                width,
                height,
                border,
            );
        }
    }

    fn copy_tex_sub_image_2d(
        &self,
        target: GLenum,
        level: GLint,
        xoffset: GLint,
        yoffset: GLint,
        x: GLint,
        y: GLint,
        width: GLsizei,
        height: GLsizei,
    ) {
        unsafe {
            self.ffi_gl_
                .CopyTexSubImage2D(target, level, xoffset, yoffset, x, y, width, height);
        }
    }

    fn copy_tex_sub_image_3d(
        &self,
        target: GLenum,
        level: GLint,
        xoffset: GLint,
        yoffset: GLint,
        zoffset: GLint,
        x: GLint,
        y: GLint,
        width: GLsizei,
        height: GLsizei,
    ) {
        unsafe {
            self.ffi_gl_.CopyTexSubImage3D(
                target, level, xoffset, yoffset, zoffset, x, y, width, height,
            );
        }
    }

    fn tex_sub_image_2d(
        &self,
        target: GLenum,
        level: GLint,
        xoffset: GLint,
        yoffset: GLint,
        width: GLsizei,
        height: GLsizei,
        format: GLenum,
        ty: GLenum,
        data: &[u8],
    ) {
        unsafe {
            self.ffi_gl_.TexSubImage2D(
                target,
                level,
                xoffset,
                yoffset,
                width,
                height,
                format,
                ty,
                data.as_ptr() as *const c_void,
            );
        }
    }

    fn tex_sub_image_2d_pbo(
        &self,
        target: GLenum,
        level: GLint,
        xoffset: GLint,
        yoffset: GLint,
        width: GLsizei,
        height: GLsizei,
        format: GLenum,
        ty: GLenum,
        offset: usize,
    ) {
        unsafe {
            self.ffi_gl_.TexSubImage2D(
                target,
                level,
                xoffset,
                yoffset,
                width,
                height,
                format,
                ty,
                offset as *const c_void,
            );
        }
    }

    fn tex_sub_image_3d(
        &self,
        target: GLenum,
        level: GLint,
        xoffset: GLint,
        yoffset: GLint,
        zoffset: GLint,
        width: GLsizei,
        height: GLsizei,
        depth: GLsizei,
        format: GLenum,
        ty: GLenum,
        data: &[u8],
    ) {
        unsafe {
            self.ffi_gl_.TexSubImage3D(
                target,
                level,
                xoffset,
                yoffset,
                zoffset,
                width,
                height,
                depth,
                format,
                ty,
                data.as_ptr() as *const c_void,
            );
        }
    }

    fn tex_sub_image_3d_pbo(
        &self,
        target: GLenum,
        level: GLint,
        xoffset: GLint,
        yoffset: GLint,
        zoffset: GLint,
        width: GLsizei,
        height: GLsizei,
        depth: GLsizei,
        format: GLenum,
        ty: GLenum,
        offset: usize,
    ) {
        unsafe {
            self.ffi_gl_.TexSubImage3D(
                target,
                level,
                xoffset,
                yoffset,
                zoffset,
                width,
                height,
                depth,
                format,
                ty,
                offset as *const c_void,
            );
        }
    }

    fn tex_storage_2d(
        &self,
        target: GLenum,
        levels: GLint,
        internal_format: GLenum,
        width: GLsizei,
        height: GLsizei,
    ) {
        if self.ffi_gl_.TexStorage2D.is_loaded() {
            unsafe {
                self.ffi_gl_
                    .TexStorage2D(target, levels, internal_format, width, height);
            }
        }
    }

    fn tex_storage_3d(
        &self,
        target: GLenum,
        levels: GLint,
        internal_format: GLenum,
        width: GLsizei,
        height: GLsizei,
        depth: GLsizei,
    ) {
        if self.ffi_gl_.TexStorage3D.is_loaded() {
            unsafe {
                self.ffi_gl_
                    .TexStorage3D(target, levels, internal_format, width, height, depth);
            }
        }
    }

    fn get_tex_image_into_buffer(
        &self,
        target: GLenum,
        level: GLint,
        format: GLenum,
        ty: GLenum,
        output: &mut [u8],
    ) {
        unsafe {
            self.ffi_gl_
                .GetTexImage(target, level, format, ty, output.as_mut_ptr() as *mut _);
        }
    }

    unsafe fn copy_image_sub_data(
        &self,
        src_name: GLuint,
        src_target: GLenum,
        src_level: GLint,
        src_x: GLint,
        src_y: GLint,
        src_z: GLint,
        dst_name: GLuint,
        dst_target: GLenum,
        dst_level: GLint,
        dst_x: GLint,
        dst_y: GLint,
        dst_z: GLint,
        src_width: GLsizei,
        src_height: GLsizei,
        src_depth: GLsizei,
    ) {
        self.ffi_gl_.CopyImageSubData(
            src_name, src_target, src_level, src_x, src_y, src_z, dst_name, dst_target, dst_level,
            dst_x, dst_y, dst_z, src_width, src_height, src_depth,
        );
    }

    fn invalidate_framebuffer(&self, target: GLenum, attachments: &[GLenum]) {
        if self.ffi_gl_.InvalidateFramebuffer.is_loaded() {
            unsafe {
                self.ffi_gl_.InvalidateFramebuffer(
                    target,
                    attachments.len() as GLsizei,
                    attachments.as_ptr(),
                );
            }
        }
    }

    fn invalidate_sub_framebuffer(
        &self,
        target: GLenum,
        attachments: &[GLenum],
        xoffset: GLint,
        yoffset: GLint,
        width: GLsizei,
        height: GLsizei,
    ) {
        if self.ffi_gl_.InvalidateSubFramebuffer.is_loaded() {
            unsafe {
                self.ffi_gl_.InvalidateSubFramebuffer(
                    target,
                    attachments.len() as GLsizei,
                    attachments.as_ptr(),
                    xoffset,
                    yoffset,
                    width,
                    height,
                );
            }
        }
    }

    #[inline]
    unsafe fn get_integer_v(&self, name: GLenum, result: &mut [GLint]) {
        assert!(!result.is_empty());
        self.ffi_gl_.GetIntegerv(name, result.as_mut_ptr());
    }

    #[inline]
    unsafe fn get_integer_64v(&self, name: GLenum, result: &mut [GLint64]) {
        assert!(!result.is_empty());
        self.ffi_gl_.GetInteger64v(name, result.as_mut_ptr());
    }

    #[inline]
    unsafe fn get_integer_iv(&self, name: GLenum, index: GLuint, result: &mut [GLint]) {
        assert!(!result.is_empty());
        self.ffi_gl_.GetIntegeri_v(name, index, result.as_mut_ptr());
    }

    #[inline]
    unsafe fn get_integer_64iv(&self, name: GLenum, index: GLuint, result: &mut [GLint64]) {
        assert!(!result.is_empty());
        self.ffi_gl_
            .GetInteger64i_v(name, index, result.as_mut_ptr());
    }

    #[inline]
    unsafe fn get_boolean_v(&self, name: GLenum, result: &mut [GLboolean]) {
        assert!(!result.is_empty());
        self.ffi_gl_.GetBooleanv(name, result.as_mut_ptr());
    }

    #[inline]
    unsafe fn get_float_v(&self, name: GLenum, result: &mut [GLfloat]) {
        assert!(!result.is_empty());
        self.ffi_gl_.GetFloatv(name, result.as_mut_ptr());
    }

    fn get_framebuffer_attachment_parameter_iv(
        &self,
        target: GLenum,
        attachment: GLenum,
        pname: GLenum,
    ) -> GLint {
        let mut result: GLint = 0;
        unsafe {
            self.ffi_gl_.GetFramebufferAttachmentParameteriv(
                target,
                attachment,
                pname,
                &mut result,
            );
        }
        result
    }

    fn get_renderbuffer_parameter_iv(&self, target: GLenum, pname: GLenum) -> GLint {
        let mut result: GLint = 0;
        unsafe {
            self.ffi_gl_
                .GetRenderbufferParameteriv(target, pname, &mut result);
        }
        result
    }

    fn get_tex_parameter_iv(&self, target: GLenum, pname: GLenum) -> GLint {
        let mut result: GLint = 0;
        unsafe {
            self.ffi_gl_.GetTexParameteriv(target, pname, &mut result);
        }
        result
    }

    fn get_tex_parameter_fv(&self, target: GLenum, pname: GLenum) -> GLfloat {
        let mut result: GLfloat = 0.0;
        unsafe {
            self.ffi_gl_.GetTexParameterfv(target, pname, &mut result);
        }
        result
    }

    fn tex_parameter_i(&self, target: GLenum, pname: GLenum, param: GLint) {
        unsafe {
            self.ffi_gl_.TexParameteri(target, pname, param);
        }
    }

    fn tex_parameter_f(&self, target: GLenum, pname: GLenum, param: GLfloat) {
        unsafe {
            self.ffi_gl_.TexParameterf(target, pname, param);
        }
    }

    fn framebuffer_texture_2d(
        &self,
        target: GLenum,
        attachment: GLenum,
        textarget: GLenum,
        texture: GLuint,
        level: GLint,
    ) {
        unsafe {
            self.ffi_gl_
                .FramebufferTexture2D(target, attachment, textarget, texture, level);
        }
    }

    fn framebuffer_texture_layer(
        &self,
        target: GLenum,
        attachment: GLenum,
        texture: GLuint,
        level: GLint,
        layer: GLint,
    ) {
        unsafe {
            self.ffi_gl_
                .FramebufferTextureLayer(target, attachment, texture, level, layer);
        }
    }

    fn blit_framebuffer(
        &self,
        src_x0: GLint,
        src_y0: GLint,
        src_x1: GLint,
        src_y1: GLint,
        dst_x0: GLint,
        dst_y0: GLint,
        dst_x1: GLint,
        dst_y1: GLint,
        mask: GLbitfield,
        filter: GLenum,
    ) {
        unsafe {
            self.ffi_gl_.BlitFramebuffer(
                src_x0, src_y0, src_x1, src_y1, dst_x0, dst_y0, dst_x1, dst_y1, mask, filter,
            );
        }
    }

    fn vertex_attrib_4f(&self, index: GLuint, x: GLfloat, y: GLfloat, z: GLfloat, w: GLfloat) {
        unsafe { self.ffi_gl_.VertexAttrib4f(index, x, y, z, w) }
    }

    fn vertex_attrib_binding(&self, attrib_index: GLuint, binding_index: GLuint) {
        unsafe { self.ffi_gl_.VertexAttribBinding(attrib_index, binding_index) }
    }

    fn vertex_attrib_pointer_f32(
        &self,
        index: GLuint,
        size: GLint,
        normalized: bool,
        stride: GLsizei,
        offset: GLuint,
    ) {
        unsafe {
            self.ffi_gl_.VertexAttribPointer(
                index,
                size,
                ffi::FLOAT,
                normalized as GLboolean,
                stride,
                offset as *const GLvoid,
            )
        }
    }

    fn vertex_attrib_pointer(
        &self,
        index: GLuint,
        size: GLint,
        type_: GLenum,
        normalized: bool,
        stride: GLsizei,
        offset: GLuint,
    ) {
        unsafe {
            self.ffi_gl_.VertexAttribPointer(
                index,
                size,
                type_,
                normalized as GLboolean,
                stride,
                offset as *const GLvoid,
            )
        }
    }

    fn vertex_attrib_i_pointer(
        &self,
        index: GLuint,
        size: GLint,
        type_: GLenum,
        stride: GLsizei,
        offset: GLuint,
    ) {
        unsafe {
            self.ffi_gl_
                .VertexAttribIPointer(index, size, type_, stride, offset as *const GLvoid)
        }
    }

    fn vertex_attrib_divisor(&self, index: GLuint, divisor: GLuint) {
        unsafe { self.ffi_gl_.VertexAttribDivisor(index, divisor) }
    }

    fn vertex_attrib_format(&self, attrib_index: GLuint, size: GLint, type_: GLenum, normalized: bool, relative_offset: GLuint) {
        unsafe { self.ffi_gl_.VertexAttribFormat(attrib_index, size, type_, normalized as GLboolean, relative_offset) }
    }

    fn vertex_attrib_i_format(&self, attrib_index: GLuint, size: GLint, type_: GLenum, relative_offset: GLuint) {
        unsafe { self.ffi_gl_.VertexAttribIFormat(attrib_index, size, type_, relative_offset) }
    }

    fn vertex_binding_divisor(&self, binding_index: GLuint, divisor: GLuint) {
        unsafe { self.ffi_gl_.VertexBindingDivisor(binding_index, divisor) }
    }

    fn viewport(&self, x: GLint, y: GLint, width: GLsizei, height: GLsizei) {
        unsafe {
            self.ffi_gl_.Viewport(x, y, width, height);
        }
    }

    fn scissor(&self, x: GLint, y: GLint, width: GLsizei, height: GLsizei) {
        unsafe {
            self.ffi_gl_.Scissor(x, y, width, height);
        }
    }

    fn line_width(&self, width: GLfloat) {
        unsafe {
            self.ffi_gl_.LineWidth(width);
        }
    }

    fn use_program(&self, program: GLuint) {
        unsafe {
            self.ffi_gl_.UseProgram(program);
        }
    }

    fn validate_program(&self, program: GLuint) {
        unsafe {
            self.ffi_gl_.ValidateProgram(program);
        }
    }

    fn draw_arrays(&self, mode: GLenum, first: GLint, count: GLsizei) {
        unsafe {
            return self.ffi_gl_.DrawArrays(mode, first, count);
        }
    }

    fn draw_arrays_instanced(
        &self,
        mode: GLenum,
        first: GLint,
        count: GLsizei,
        primcount: GLsizei,
    ) {
        unsafe {
            return self
                .ffi_gl_
                .DrawArraysInstanced(mode, first, count, primcount);
        }
    }

    fn draw_elements(
        &self,
        mode: GLenum,
        count: GLsizei,
        element_type: GLenum,
        indices_offset: GLuint,
    ) {
        unsafe {
            return self.ffi_gl_.DrawElements(
                mode,
                count,
                element_type,
                indices_offset as *const c_void,
            );
        }
    }

    fn draw_elements_instanced(
        &self,
        mode: GLenum,
        count: GLsizei,
        element_type: GLenum,
        indices_offset: GLuint,
        primcount: GLsizei,
    ) {
        unsafe {
            return self.ffi_gl_.DrawElementsInstanced(
                mode,
                count,
                element_type,
                indices_offset as *const c_void,
                primcount,
            );
        }
    }

    fn blend_color(&self, r: f32, g: f32, b: f32, a: f32) {
        unsafe {
            self.ffi_gl_.BlendColor(r, g, b, a);
        }
    }

    fn blend_func(&self, sfactor: GLenum, dfactor: GLenum) {
        unsafe {
            self.ffi_gl_.BlendFunc(sfactor, dfactor);
        }
    }

    fn blend_func_separate(
        &self,
        src_rgb: GLenum,
        dest_rgb: GLenum,
        src_alpha: GLenum,
        dest_alpha: GLenum,
    ) {
        unsafe {
            self.ffi_gl_
                .BlendFuncSeparate(src_rgb, dest_rgb, src_alpha, dest_alpha);
        }
    }

    fn blend_equation(&self, mode: GLenum) {
        unsafe {
            self.ffi_gl_.BlendEquation(mode);
        }
    }

    fn blend_equation_separate(&self, mode_rgb: GLenum, mode_alpha: GLenum) {
        unsafe {
            self.ffi_gl_.BlendEquationSeparate(mode_rgb, mode_alpha);
        }
    }

    fn color_mask(&self, r: bool, g: bool, b: bool, a: bool) {
        unsafe {
            self.ffi_gl_.ColorMask(
                r as GLboolean,
                g as GLboolean,
                b as GLboolean,
                a as GLboolean,
            );
        }
    }

    fn cull_face(&self, mode: GLenum) {
        unsafe {
            self.ffi_gl_.CullFace(mode);
        }
    }

    fn front_face(&self, mode: GLenum) {
        unsafe {
            self.ffi_gl_.FrontFace(mode);
        }
    }

    fn enable(&self, cap: GLenum) {
        unsafe {
            self.ffi_gl_.Enable(cap);
        }
    }

    fn disable(&self, cap: GLenum) {
        unsafe {
            self.ffi_gl_.Disable(cap);
        }
    }

    fn hint(&self, param_name: GLenum, param_val: GLenum) {
        unsafe {
            self.ffi_gl_.Hint(param_name, param_val);
        }
    }

    fn is_enabled(&self, cap: GLenum) -> GLboolean {
        unsafe { self.ffi_gl_.IsEnabled(cap) }
    }

    fn is_shader(&self, shader: GLuint) -> GLboolean {
        unsafe { self.ffi_gl_.IsShader(shader) }
    }

    fn is_texture(&self, texture: GLenum) -> GLboolean {
        unsafe { self.ffi_gl_.IsTexture(texture) }
    }

    fn is_framebuffer(&self, framebuffer: GLenum) -> GLboolean {
        unsafe { self.ffi_gl_.IsFramebuffer(framebuffer) }
    }

    fn is_renderbuffer(&self, renderbuffer: GLenum) -> GLboolean {
        unsafe { self.ffi_gl_.IsRenderbuffer(renderbuffer) }
    }

    fn check_frame_buffer_status(&self, target: GLenum) -> GLenum {
        unsafe { self.ffi_gl_.CheckFramebufferStatus(target) }
    }

    fn enable_vertex_attrib_array(&self, index: GLuint) {
        unsafe {
            self.ffi_gl_.EnableVertexAttribArray(index);
        }
    }

    fn disable_vertex_attrib_array(&self, index: GLuint) {
        unsafe {
            self.ffi_gl_.DisableVertexAttribArray(index);
        }
    }

    fn uniform_1f(&self, location: GLint, v0: GLfloat) {
        unsafe {
            self.ffi_gl_.Uniform1f(location, v0);
        }
    }

    fn uniform_1fv(&self, location: GLint, values: &[f32]) {
        unsafe {
            self.ffi_gl_
                .Uniform1fv(location, values.len() as GLsizei, values.as_ptr());
        }
    }

    fn uniform_1i(&self, location: GLint, v0: GLint) {
        unsafe {
            self.ffi_gl_.Uniform1i(location, v0);
        }
    }

    fn uniform_1iv(&self, location: GLint, values: &[i32]) {
        unsafe {
            self.ffi_gl_
                .Uniform1iv(location, values.len() as GLsizei, values.as_ptr());
        }
    }

    fn uniform_1ui(&self, location: GLint, v0: GLuint) {
        unsafe {
            self.ffi_gl_.Uniform1ui(location, v0);
        }
    }

    fn uniform_2f(&self, location: GLint, v0: GLfloat, v1: GLfloat) {
        unsafe {
            self.ffi_gl_.Uniform2f(location, v0, v1);
        }
    }

    fn uniform_2fv(&self, location: GLint, values: &[f32]) {
        unsafe {
            self.ffi_gl_
                .Uniform2fv(location, (values.len() / 2) as GLsizei, values.as_ptr());
        }
    }

    fn uniform_2i(&self, location: GLint, v0: GLint, v1: GLint) {
        unsafe {
            self.ffi_gl_.Uniform2i(location, v0, v1);
        }
    }

    fn uniform_2iv(&self, location: GLint, values: &[i32]) {
        unsafe {
            self.ffi_gl_
                .Uniform2iv(location, (values.len() / 2) as GLsizei, values.as_ptr());
        }
    }

    fn uniform_2ui(&self, location: GLint, v0: GLuint, v1: GLuint) {
        unsafe {
            self.ffi_gl_.Uniform2ui(location, v0, v1);
        }
    }

    fn uniform_3f(&self, location: GLint, v0: GLfloat, v1: GLfloat, v2: GLfloat) {
        unsafe {
            self.ffi_gl_.Uniform3f(location, v0, v1, v2);
        }
    }

    fn uniform_3fv(&self, location: GLint, values: &[f32]) {
        unsafe {
            self.ffi_gl_
                .Uniform3fv(location, (values.len() / 3) as GLsizei, values.as_ptr());
        }
    }

    fn uniform_3i(&self, location: GLint, v0: GLint, v1: GLint, v2: GLint) {
        unsafe {
            self.ffi_gl_.Uniform3i(location, v0, v1, v2);
        }
    }

    fn uniform_3iv(&self, location: GLint, values: &[i32]) {
        unsafe {
            self.ffi_gl_
                .Uniform3iv(location, (values.len() / 3) as GLsizei, values.as_ptr());
        }
    }

    fn uniform_3ui(&self, location: GLint, v0: GLuint, v1: GLuint, v2: GLuint) {
        unsafe {
            self.ffi_gl_.Uniform3ui(location, v0, v1, v2);
        }
    }

    fn uniform_4f(&self, location: GLint, x: GLfloat, y: GLfloat, z: GLfloat, w: GLfloat) {
        unsafe {
            self.ffi_gl_.Uniform4f(location, x, y, z, w);
        }
    }

    fn uniform_4i(&self, location: GLint, x: GLint, y: GLint, z: GLint, w: GLint) {
        unsafe {
            self.ffi_gl_.Uniform4i(location, x, y, z, w);
        }
    }

    fn uniform_4iv(&self, location: GLint, values: &[i32]) {
        unsafe {
            self.ffi_gl_
                .Uniform4iv(location, (values.len() / 4) as GLsizei, values.as_ptr());
        }
    }

    fn uniform_4ui(&self, location: GLint, x: GLuint, y: GLuint, z: GLuint, w: GLuint) {
        unsafe {
            self.ffi_gl_.Uniform4ui(location, x, y, z, w);
        }
    }

    fn uniform_4fv(&self, location: GLint, values: &[f32]) {
        unsafe {
            self.ffi_gl_
                .Uniform4fv(location, (values.len() / 4) as GLsizei, values.as_ptr());
        }
    }

    fn uniform_matrix_2fv(&self, location: GLint, transpose: bool, value: &[f32]) {
        unsafe {
            self.ffi_gl_.UniformMatrix2fv(
                location,
                (value.len() / 4) as GLsizei,
                transpose as GLboolean,
                value.as_ptr(),
            );
        }
    }

    fn uniform_matrix_3fv(&self, location: GLint, transpose: bool, value: &[f32]) {
        unsafe {
            self.ffi_gl_.UniformMatrix3fv(
                location,
                (value.len() / 9) as GLsizei,
                transpose as GLboolean,
                value.as_ptr(),
            );
        }
    }

    fn uniform_matrix_4fv(&self, location: GLint, transpose: bool, value: &[f32]) {
        unsafe {
            self.ffi_gl_.UniformMatrix4fv(
                location,
                (value.len() / 16) as GLsizei,
                transpose as GLboolean,
                value.as_ptr(),
            );
        }
    }

    fn depth_mask(&self, flag: bool) {
        unsafe {
            self.ffi_gl_.DepthMask(flag as GLboolean);
        }
    }

    fn depth_range(&self, near: f64, far: f64) {
        unsafe {
            self.ffi_gl_.DepthRange(near as GLclampd, far as GLclampd);
        }
    }

    fn get_active_attrib(&self, program: GLuint, index: GLuint) -> (i32, u32, String) {
        let mut buf_size = [0];
        unsafe {
            self.get_program_iv(program, ffi::ACTIVE_ATTRIBUTE_MAX_LENGTH, &mut buf_size);
        }
        let mut name = vec![0u8; buf_size[0] as usize];
        let mut length = 0 as GLsizei;
        let mut size = 0 as i32;
        let mut type_ = 0 as u32;
        unsafe {
            self.ffi_gl_.GetActiveAttrib(
                program,
                index,
                buf_size[0],
                &mut length,
                &mut size,
                &mut type_,
                name.as_mut_ptr() as *mut GLchar,
            );
        }
        name.truncate(if length > 0 { length as usize } else { 0 });
        (size, type_, String::from_utf8(name).unwrap())
    }

    fn get_active_uniform(&self, program: GLuint, index: GLuint) -> (i32, u32, String) {
        let mut buf_size = [0];
        unsafe {
            self.get_program_iv(program, ffi::ACTIVE_UNIFORM_MAX_LENGTH, &mut buf_size);
        }
        let mut name = vec![0 as u8; buf_size[0] as usize];
        let mut length: GLsizei = 0;
        let mut size: i32 = 0;
        let mut type_: u32 = 0;

        unsafe {
            self.ffi_gl_.GetActiveUniform(
                program,
                index,
                buf_size[0],
                &mut length,
                &mut size,
                &mut type_,
                name.as_mut_ptr() as *mut GLchar,
            );
        }

        name.truncate(if length > 0 { length as usize } else { 0 });

        (size, type_, String::from_utf8(name).unwrap())
    }

    fn get_active_uniforms_iv(
        &self,
        program: GLuint,
        indices: Vec<GLuint>,
        pname: GLenum,
    ) -> Vec<GLint> {
        let mut result = Vec::with_capacity(indices.len());
        unsafe {
            result.set_len(indices.len());
            self.ffi_gl_.GetActiveUniformsiv(
                program,
                indices.len() as GLsizei,
                indices.as_ptr(),
                pname,
                result.as_mut_ptr(),
            );
        }
        result
    }

    fn get_active_uniform_block_i(&self, program: GLuint, index: GLuint, pname: GLenum) -> GLint {
        let mut result = 0;
        unsafe {
            self.ffi_gl_
                .GetActiveUniformBlockiv(program, index, pname, &mut result);
        }
        result
    }

    fn get_active_uniform_block_iv(
        &self,
        program: GLuint,
        index: GLuint,
        pname: GLenum,
    ) -> Vec<GLint> {
        let count =
            self.get_active_uniform_block_i(program, index, ffi::UNIFORM_BLOCK_ACTIVE_UNIFORMS);
        let mut result = Vec::with_capacity(count as usize);
        unsafe {
            result.set_len(count as usize);
            self.ffi_gl_
                .GetActiveUniformBlockiv(program, index, pname, result.as_mut_ptr());
        }
        result
    }

    fn get_active_uniform_block_name(&self, program: GLuint, index: GLuint) -> String {
        let buf_size =
            self.get_active_uniform_block_i(program, index, ffi::UNIFORM_BLOCK_NAME_LENGTH);
        let mut name = vec![0 as u8; buf_size as usize];
        let mut length: GLsizei = 0;
        unsafe {
            self.ffi_gl_.GetActiveUniformBlockName(
                program,
                index,
                buf_size,
                &mut length,
                name.as_mut_ptr() as *mut GLchar,
            );
        }
        name.truncate(if length > 0 { length as usize } else { 0 });

        String::from_utf8(name).unwrap()
    }

    fn get_attrib_location(&self, program: GLuint, name: &str) -> c_int {
        let name = CString::new(name).unwrap();
        unsafe { self.ffi_gl_.GetAttribLocation(program, name.as_ptr()) }
    }

    fn get_frag_data_location(&self, program: GLuint, name: &str) -> c_int {
        let name = CString::new(name).unwrap();
        unsafe { self.ffi_gl_.GetFragDataLocation(program, name.as_ptr()) }
    }

    fn get_uniform_location(&self, program: GLuint, name: &str) -> c_int {
        let name = CString::new(name).unwrap();
        unsafe { self.ffi_gl_.GetUniformLocation(program, name.as_ptr()) }
    }

    fn get_program_info_log(&self, program: GLuint) -> String {
        let mut max_len = [0];
        unsafe {
            self.get_program_iv(program, ffi::INFO_LOG_LENGTH, &mut max_len);
        }
        if max_len[0] == 0 {
            return String::new();
        }
        let mut result = vec![0u8; max_len[0] as usize];
        let mut result_len = 0 as GLsizei;
        unsafe {
            self.ffi_gl_.GetProgramInfoLog(
                program,
                max_len[0] as GLsizei,
                &mut result_len,
                result.as_mut_ptr() as *mut GLchar,
            );
        }
        result.truncate(if result_len > 0 {
            result_len as usize
        } else {
            0
        });
        String::from_utf8(result).unwrap()
    }

    #[inline]
    unsafe fn get_program_iv(&self, program: GLuint, pname: GLenum, result: &mut [GLint]) {
        assert!(!result.is_empty());
        self.ffi_gl_
            .GetProgramiv(program, pname, result.as_mut_ptr());
    }

    fn get_program_binary(&self, program: GLuint) -> (Vec<u8>, GLenum) {
        if !self.ffi_gl_.GetProgramBinary.is_loaded() {
            return (Vec::new(), NONE);
        }
        let mut len = [0];
        unsafe {
            self.get_program_iv(program, ffi::PROGRAM_BINARY_LENGTH, &mut len);
        }
        if len[0] <= 0 {
            return (Vec::new(), NONE);
        }
        let mut binary: Vec<u8> = Vec::with_capacity(len[0] as usize);
        let mut format = NONE;
        let mut out_len = 0;
        unsafe {
            binary.set_len(len[0] as usize);
            self.ffi_gl_.GetProgramBinary(
                program,
                len[0],
                &mut out_len as *mut GLsizei,
                &mut format,
                binary.as_mut_ptr() as *mut c_void,
            );
        }
        if len[0] != out_len {
            return (Vec::new(), NONE);
        }

        (binary, format)
    }

    fn program_binary(&self, program: GLuint, format: GLenum, binary: &[u8]) {
        if !self.ffi_gl_.ProgramBinary.is_loaded() {
            return;
        }
        unsafe {
            self.ffi_gl_.ProgramBinary(
                program,
                format,
                binary.as_ptr() as *const c_void,
                binary.len() as GLsizei,
            );
        }
    }

    fn program_parameter_i(&self, program: GLuint, pname: GLenum, value: GLint) {
        if !self.ffi_gl_.ProgramParameteri.is_loaded() {
            return;
        }
        unsafe {
            self.ffi_gl_.ProgramParameteri(program, pname, value);
        }
    }

    #[inline]
    unsafe fn get_vertex_attrib_iv(&self, index: GLuint, pname: GLenum, result: &mut [GLint]) {
        assert!(!result.is_empty());
        self.ffi_gl_
            .GetVertexAttribiv(index, pname, result.as_mut_ptr());
    }

    #[inline]
    unsafe fn get_vertex_attrib_fv(&self, index: GLuint, pname: GLenum, result: &mut [GLfloat]) {
        assert!(!result.is_empty());
        self.ffi_gl_
            .GetVertexAttribfv(index, pname, result.as_mut_ptr());
    }

    fn get_vertex_attrib_pointer_v(&self, index: GLuint, pname: GLenum) -> GLsizeiptr {
        let mut result = 0 as *mut GLvoid;
        unsafe {
            self.ffi_gl_
                .GetVertexAttribPointerv(index, pname, &mut result)
        }
        result as GLsizeiptr
    }

    fn get_buffer_parameter_iv(&self, target: GLuint, pname: GLenum) -> GLint {
        let mut result = 0 as GLint;
        unsafe {
            self.ffi_gl_
                .GetBufferParameteriv(target, pname, &mut result);
        }
        result
    }

    fn get_shader_info_log(&self, shader: GLuint) -> String {
        let mut max_len = [0];
        unsafe {
            self.get_shader_iv(shader, ffi::INFO_LOG_LENGTH, &mut max_len);
        }
        if max_len[0] == 0 {
            return String::new();
        }
        let mut result = vec![0u8; max_len[0] as usize];
        let mut result_len = 0 as GLsizei;
        unsafe {
            self.ffi_gl_.GetShaderInfoLog(
                shader,
                max_len[0] as GLsizei,
                &mut result_len,
                result.as_mut_ptr() as *mut GLchar,
            );
        }
        result.truncate(if result_len > 0 {
            result_len as usize
        } else {
            0
        });
        String::from_utf8(result).unwrap()
    }

    fn get_string(&self, which: GLenum) -> String {
        unsafe {
            let llstr = self.ffi_gl_.GetString(which);
            if !llstr.is_null() {
                return str::from_utf8_unchecked(CStr::from_ptr(llstr as *const c_char).to_bytes())
                    .to_string();
            } else {
                return "".to_string();
            }
        }
    }

    fn get_string_i(&self, which: GLenum, index: GLuint) -> String {
        unsafe {
            let llstr = self.ffi_gl_.GetStringi(which, index);
            if !llstr.is_null() {
                str::from_utf8_unchecked(CStr::from_ptr(llstr as *const c_char).to_bytes())
                    .to_string()
            } else {
                "".to_string()
            }
        }
    }

    unsafe fn get_shader_iv(&self, shader: GLuint, pname: GLenum, result: &mut [GLint]) {
        assert!(!result.is_empty());
        self.ffi_gl_.GetShaderiv(shader, pname, result.as_mut_ptr());
    }

    fn get_shader_precision_format(
        &self,
        _shader_type: GLuint,
        precision_type: GLuint,
    ) -> (GLint, GLint, GLint) {
        // gl.GetShaderPrecisionFormat is not available until OpenGL 4.1.
        // Fallback to OpenGL standard precissions that most desktop hardware support.
        match precision_type {
            ffi::LOW_FLOAT | ffi::MEDIUM_FLOAT | ffi::HIGH_FLOAT => {
                // Fallback to IEEE 754 single precision
                // Range: from -2^127 to 2^127
                // Significand precision: 23 bits
                (127, 127, 23)
            }
            ffi::LOW_INT | ffi::MEDIUM_INT | ffi::HIGH_INT => {
                // Fallback to single precision integer
                // Range: from -2^24 to 2^24
                // Precision: For integer formats this value is always 0
                (24, 24, 0)
            }
            _ => (0, 0, 0),
        }
    }

    fn compile_shader(&self, shader: GLuint) {
        unsafe {
            self.ffi_gl_.CompileShader(shader);
        }
    }

    fn create_program(&self) -> GLuint {
        unsafe {
            return self.ffi_gl_.CreateProgram();
        }
    }

    fn delete_program(&self, program: GLuint) {
        unsafe {
            self.ffi_gl_.DeleteProgram(program);
        }
    }

    fn create_shader(&self, shader_type: GLenum) -> GLuint {
        unsafe {
            return self.ffi_gl_.CreateShader(shader_type);
        }
    }

    fn delete_shader(&self, shader: GLuint) {
        unsafe {
            self.ffi_gl_.DeleteShader(shader);
        }
    }

    fn detach_shader(&self, program: GLuint, shader: GLuint) {
        unsafe {
            self.ffi_gl_.DetachShader(program, shader);
        }
    }

    fn link_program(&self, program: GLuint) {
        unsafe {
            return self.ffi_gl_.LinkProgram(program);
        }
    }

    fn clear_color(&self, r: f32, g: f32, b: f32, a: f32) {
        unsafe {
            self.ffi_gl_.ClearColor(r, g, b, a);
        }
    }

    fn clear(&self, buffer_mask: GLbitfield) {
        unsafe {
            self.ffi_gl_.Clear(buffer_mask);
        }
    }

    fn clear_depth(&self, depth: f64) {
        unsafe {
            self.ffi_gl_.ClearDepth(depth as GLclampd);
        }
    }

    fn clear_stencil(&self, s: GLint) {
        unsafe {
            self.ffi_gl_.ClearStencil(s);
        }
    }

    fn flush(&self) {
        unsafe {
            self.ffi_gl_.Flush();
        }
    }

    fn finish(&self) {
        unsafe {
            self.ffi_gl_.Finish();
        }
    }

    fn get_error(&self) -> GLenum {
        unsafe { self.ffi_gl_.GetError() }
    }

    fn stencil_mask(&self, mask: GLuint) {
        unsafe { self.ffi_gl_.StencilMask(mask) }
    }

    fn stencil_mask_separate(&self, face: GLenum, mask: GLuint) {
        unsafe { self.ffi_gl_.StencilMaskSeparate(face, mask) }
    }

    fn stencil_func(&self, func: GLenum, ref_: GLint, mask: GLuint) {
        unsafe { self.ffi_gl_.StencilFunc(func, ref_, mask) }
    }

    fn stencil_func_separate(&self, face: GLenum, func: GLenum, ref_: GLint, mask: GLuint) {
        unsafe { self.ffi_gl_.StencilFuncSeparate(face, func, ref_, mask) }
    }

    fn stencil_op(&self, sfail: GLenum, dpfail: GLenum, dppass: GLenum) {
        unsafe { self.ffi_gl_.StencilOp(sfail, dpfail, dppass) }
    }

    fn stencil_op_separate(&self, face: GLenum, sfail: GLenum, dpfail: GLenum, dppass: GLenum) {
        unsafe { self.ffi_gl_.StencilOpSeparate(face, sfail, dpfail, dppass) }
    }

    #[allow(unused_variables)]
    fn egl_image_target_texture2d_oes(&self, target: GLenum, image: GLeglImageOES) {
        panic!("not supported")
    }

    #[allow(unused_variables)]
    fn egl_image_target_renderbuffer_storage_oes(&self, target: GLenum, image: GLeglImageOES) {
        panic!("not supported")
    }

    fn generate_mipmap(&self, target: GLenum) {
        unsafe { self.ffi_gl_.GenerateMipmap(target) }
    }

    fn insert_event_marker_ext(&self, message: &str) {
        if self.ffi_gl_.InsertEventMarkerEXT.is_loaded() {
            unsafe {
                self.ffi_gl_
                    .InsertEventMarkerEXT(message.len() as GLsizei, message.as_ptr() as *const _);
            }
        }
    }

    fn push_group_marker_ext(&self, message: &str) {
        if self.ffi_gl_.PushGroupMarkerEXT.is_loaded() {
            unsafe {
                self.ffi_gl_
                    .PushGroupMarkerEXT(message.len() as GLsizei, message.as_ptr() as *const _);
            }
        }
    }

    fn pop_group_marker_ext(&self) {
        if self.ffi_gl_.PopGroupMarkerEXT.is_loaded() {
            unsafe {
                self.ffi_gl_.PopGroupMarkerEXT();
            }
        }
    }

    fn debug_message_insert_khr(&self, source: GLenum, type_: GLenum, id: GLuint, severity: GLenum, message: &str) {
        if self.ffi_gl_.DebugMessageInsertKHR.is_loaded() {
            unsafe {
                self.ffi_gl_
                    .DebugMessageInsertKHR(source, type_, id, severity, message.len() as GLsizei, message.as_ptr() as *const _);
            }
        }
    }

    fn push_debug_group_khr(&self, source: GLenum, id: GLuint, message: &str) {
        if self.ffi_gl_.PushDebugGroupKHR.is_loaded() {
            unsafe {
                self.ffi_gl_
                    .PushDebugGroupKHR(source, id, message.len() as GLsizei, message.as_ptr() as *const _);
            }
        }
    }

    fn pop_debug_group_khr(&self) {
        if self.ffi_gl_.PopDebugGroupKHR.is_loaded() {
            unsafe {
                self.ffi_gl_.PopDebugGroupKHR();
            }
        }
    }

    fn fence_sync(&self, condition: GLenum, flags: GLbitfield) -> GLsync {
        unsafe { self.ffi_gl_.FenceSync(condition, flags) as *const _ }
    }

    fn client_wait_sync(&self, sync: GLsync, flags: GLbitfield, timeout: GLuint64) -> GLenum {
        unsafe {
            self.ffi_gl_
                .ClientWaitSync(sync as *const _, flags, timeout)
        }
    }

    fn wait_sync(&self, sync: GLsync, flags: GLbitfield, timeout: GLuint64) {
        unsafe {
            self.ffi_gl_.WaitSync(sync as *const _, flags, timeout);
        }
    }

    fn texture_range_apple(&self, target: GLenum, data: &[u8]) {
        unsafe {
            self.ffi_gl_.TextureRangeAPPLE(
                target,
                data.len() as GLsizei,
                data.as_ptr() as *const c_void,
            );
        }
    }

    fn delete_sync(&self, sync: GLsync) {
        unsafe {
            self.ffi_gl_.DeleteSync(sync as *const _);
        }
    }

    fn gen_fences_apple(&self, n: GLsizei) -> Vec<GLuint> {
        let mut result = vec![0 as GLuint; n as usize];
        unsafe {
            self.ffi_gl_.GenFencesAPPLE(n, result.as_mut_ptr());
        }
        result
    }

    fn delete_fences_apple(&self, fences: &[GLuint]) {
        unsafe {
            self.ffi_gl_
                .DeleteFencesAPPLE(fences.len() as GLsizei, fences.as_ptr());
        }
    }

    fn set_fence_apple(&self, fence: GLuint) {
        unsafe {
            self.ffi_gl_.SetFenceAPPLE(fence);
        }
    }

    fn finish_fence_apple(&self, fence: GLuint) {
        unsafe {
            self.ffi_gl_.FinishFenceAPPLE(fence);
        }
    }

    fn test_fence_apple(&self, fence: GLuint) {
        unsafe {
            self.ffi_gl_.TestFenceAPPLE(fence);
        }
    }

    fn test_object_apple(&self, object: GLenum, name: GLuint) -> GLboolean {
        unsafe {
            self.ffi_gl_.TestObjectAPPLE(object, name)
        }
    }

    fn finish_object_apple(&self, object: GLenum, name: GLuint) {
        unsafe {
            // the spec has a typo for name as GLint instead of GLuint
            self.ffi_gl_.FinishObjectAPPLE(object, name as GLint);
        }
    }

    // GL_ARB_blend_func_extended
    fn bind_frag_data_location_indexed(
        &self,
        program: GLuint,
        color_number: GLuint,
        index: GLuint,
        name: &str,
    ) {
        if !self.ffi_gl_.BindFragDataLocationIndexed.is_loaded() {
            return;
        }

        let c_string = CString::new(name).unwrap();

        unsafe {
            self.ffi_gl_.BindFragDataLocationIndexed(
                program,
                color_number,
                index,
                c_string.as_ptr(),
            )
        }
    }

    fn get_frag_data_index(&self, program: GLuint, name: &str) -> GLint {
        if !self.ffi_gl_.GetFragDataIndex.is_loaded() {
            return -1;
        }

        let c_string = CString::new(name).unwrap();

        unsafe { self.ffi_gl_.GetFragDataIndex(program, c_string.as_ptr()) }
    }

    // GL_KHR_debug
    fn get_debug_messages(&self) -> Vec<DebugMessage> {
        if !self.ffi_gl_.GetDebugMessageLog.is_loaded() {
            return Vec::new();
        }

        let mut max_message_len = 0;
        unsafe {
            self.ffi_gl_
                .GetIntegerv(ffi::MAX_DEBUG_MESSAGE_LENGTH, &mut max_message_len)
        }

        let mut output = Vec::new();
        const CAPACITY: usize = 4;

        let mut msg_data = vec![0u8; CAPACITY * max_message_len as usize];
        let mut sources = [0 as GLenum; CAPACITY];
        let mut types = [0 as GLenum; CAPACITY];
        let mut severities = [0 as GLenum; CAPACITY];
        let mut ids = [0 as GLuint; CAPACITY];
        let mut lengths = [0 as GLsizei; CAPACITY];

        loop {
            let count = unsafe {
                self.ffi_gl_.GetDebugMessageLog(
                    CAPACITY as _,
                    msg_data.len() as _,
                    sources.as_mut_ptr(),
                    types.as_mut_ptr(),
                    ids.as_mut_ptr(),
                    severities.as_mut_ptr(),
                    lengths.as_mut_ptr(),
                    msg_data.as_mut_ptr() as *mut _,
                )
            };

            let mut offset = 0;
            output.extend((0..count as usize).map(|i| {
                let len = lengths[i] as usize;
                let slice = &msg_data[offset..offset + len];
                offset += len;
                DebugMessage {
                    message: String::from_utf8_lossy(slice).to_string(),
                    source: sources[i],
                    ty: types[i],
                    id: ids[i],
                    severity: severities[i],
                }
            }));

            if (count as usize) < CAPACITY {
                return output;
            }
        }
    }

    fn provoking_vertex_angle(&self, _mode: GLenum) {
        unimplemented!("This extension is GLES only");
    }

    // GL_KHR_blend_equation_advanced
    fn blend_barrier_khr(&self) {
        if self.ffi_gl_.BlendBarrierKHR.is_loaded() {
            unsafe {
                self.ffi_gl_.BlendBarrierKHR();
            }
        }
    }

    // GL_CHROMIUM_copy_texture
    fn copy_texture_chromium(&self,
        _source_id: GLuint, _source_level: GLint,
        _dest_target: GLenum, _dest_id: GLuint, _dest_level: GLint,
        _internal_format: GLint, _dest_type: GLenum,
        _unpack_flip_y: GLboolean, _unpack_premultiply_alpha: GLboolean, _unpack_unmultiply_alpha: GLboolean)
    {
        unimplemented!("This extension is GLES only");
    }
    fn copy_sub_texture_chromium(&self,
        _source_id: GLuint, _source_level: GLint,
        _dest_target: GLenum, _dest_id: GLuint, _dest_level: GLint,
        _x_offset: GLint, _y_offset: GLint, _x: GLint, _y: GLint, _width: GLsizei, _height: GLsizei,
        _unpack_flip_y: GLboolean, _unpack_premultiply_alpha: GLboolean, _unpack_unmultiply_alpha: GLboolean)
    {
        unimplemented!("This extension is GLES only");
    }

    // GL_ANGLE_copy_texture_3d
    fn copy_texture_3d_angle(
        &self,
        _source_id: GLuint,
        _source_level: GLint,
        _dest_target: GLenum,
        _dest_id: GLuint,
        _dest_level: GLint,
        _internal_format: GLint,
        _dest_type: GLenum,
        _unpack_flip_y: GLboolean,
        _unpack_premultiply_alpha: GLboolean,
        _unpack_unmultiply_alpha: GLboolean,
    ) {
        unimplemented!("This extension is ANGLE only");
    }

    fn copy_sub_texture_3d_angle(
        &self,
        _source_id: GLuint,
        _source_level: GLint,
        _dest_target: GLenum,
        _dest_id: GLuint,
        _dest_level: GLint,
        _x_offset: GLint,
        _y_offset: GLint,
        _z_offset: GLint,
        _x: GLint,
        _y: GLint,
        _z: GLint,
        _width: GLsizei,
        _height: GLsizei,
        _depth: GLsizei,
        _unpack_flip_y: GLboolean,
        _unpack_premultiply_alpha: GLboolean,
        _unpack_unmultiply_alpha: GLboolean,
    ) {
        unimplemented!("This extension is ANGLE only");
    }

    fn buffer_storage(
        &self,
        target: GLenum,
        size: GLsizeiptr,
        data: *const GLvoid,
        flags: GLbitfield,
    ) {
        unsafe {
            self.ffi_gl_.BufferStorage(target, size, data, flags);
        }
    }

    fn flush_mapped_buffer_range(&self, target: GLenum, offset: GLintptr, length: GLsizeiptr) {
        unsafe {
            self.ffi_gl_.FlushMappedBufferRange(target, offset, length);
        }
    }

    fn start_tiling_qcom(&self, _x: GLuint, _y: GLuint, _width: GLuint, _height: GLuint, _preserve_mask: GLbitfield) {
    }

    fn end_tiling_qcom(&self, _preserve_mask: GLbitfield) {
    }
}