Function apply 

pub fn apply(
    fe: &DisplacementMap,
    sx: f32,
    sy: f32,
    src: ImageRef<'_>,
    map: ImageRef<'_>,
    dest: ImageRefMut<'_>,
)

Applies a displacement map.

• map pixels should have a unpremultiplied alpha.
• src pixels can have any alpha method.

sx and sy indicate canvas scale.

Panics

When src, map and dest have different sizes.