Struct tiny_skia::alpha_runs::AlphaRuns

pub struct AlphaRuns {
    pub runs: Vec<Option<NonZeroU16>>,
    pub alpha: Vec<u8>,
}

Sparse array of run-length-encoded alpha (supersampling coverage) values.

Sparseness allows us to independently compose several paths into the same AlphaRuns buffer.

Fields

runs: Vec<Option<NonZeroU16>>

alpha: Vec<u8>

Implementations

impl AlphaRuns

pub fn new(width: NonZeroU32) -> Self

pub fn catch_overflow(alpha: u16) -> u8

Returns 0-255 given 0-256.

pub fn is_empty(&self) -> bool

Returns true if the scanline contains only a single run, of alpha value 0.

pub fn reset(&mut self, width: NonZeroU32)

Reinitialize for a new scanline.

pub fn add( &mut self, x: u32, start_alpha: u8, middle_count: usize, stop_alpha: u8, max_value: u8, offset_x: usize, ) -> usize

Insert into the buffer a run starting at (x-offset_x).

if start_alpha > 0 one pixel with value += start_alpha, max 255 if middle_count > 0 middle_count pixels with value += max_value if stop_alpha > 0 one pixel with value += stop_alpha

Returns the offset_x value that should be passed on the next call, assuming we’re on the same scanline. If the caller is switching scanlines, then offset_x should be 0 when this is called.

fn break_run( runs: &mut [Option<NonZeroU16>], alpha: &mut [u8], x: usize, count: usize, )

Break the runs in the buffer at offsets x and x+count, properly updating the runs to the right and left.

i.e. from the state AAAABBBB, run-length encoded as A4B4, break_run(…, 2, 5) would produce AAAABBBB rle as A2A2B3B1. Allows add() to sum another run to some of the new sub-runs. i.e. adding ..CCCCC. would produce AADDEEEB, rle as A2D2E3B1.

pub fn break_at(alpha: &mut [u8], runs: &mut [Option<NonZeroU16>], x: i32)

Cut (at offset x in the buffer) a run into two shorter runs with matching alpha values.

Used by the RectClipBlitter to trim a RLE encoding to match the clipping rectangle.