Module blend

Blend modes and the per-pixel composite of a straight-alpha RGBA layer onto an opaque canvas.

Functions

blend_channel

Blend one channel: s = layer (source), d = canvas (destination), both 0..1. Returns 0..1.

composite_rect

Composite layer (straight-alpha RGBA, same size as dst) onto dst (opaque canvas) with the given blend mode and global opacity, restricted to the pixel rect [x0, x1) × [y0, y1) (clamped to the canvas). Pixels with alpha 0 are skipped.

composite_row

Composite one row of straight-alpha RGBA pixels (src) onto one row of opaque canvas pixels (dst). Both slices are 4 * n bytes; opacity is 0..1. Canvas alpha stays 255.

div255 🔒

x / 255 rounded, for x <= 255*255.