Module image_mask 

Anti-aliased alpha masking for raster images — circle / rounded-square / square coverage applied in-place to RGBA8 pixel buffers.

The retained renderer’s Canvas::set_clip is rectangular-only, so to crop a photo into a circle (avatar, contact icon, channel thumbnail, etc.) we modulate the source image’s alpha channel with a per-pixel coverage value computed analytically. 4×4 super-sampling (16 sub-samples per pixel) gives a smooth edge at the small sizes these masks are typically used at (≤96 logical pixels).

Used directly by ImageWidget::mask and by Avatar. Other widgets that want a non-rectangular image silhouette can call apply_alpha_mask and center_crop_square directly.

let mut pixels = vec![255u8; 32 * 32 * 4]; // opaque white 32×32
apply_alpha_mask(&mut pixels, 32, 32, ImageMaskShape::Circle);
// Corner pixels are now transparent; the center is still opaque.
assert_eq!(pixels[3], 0);         // top-left alpha
assert_eq!(pixels[(16 * 32 + 16) * 4 + 3], 255); // center alpha

Enums

ImageMaskShape

Shape of the alpha mask applied to an image.

Functions

apply_alpha_mask

Apply an alpha mask in-place to an RGBA8 buffer. RGB channels are preserved; only alpha is modulated by the coverage value, so a pre-multiplied source remains pre-multiplied (the alpha-channel-only transformation matches RasterIcon::to_alpha_mask).

center_crop_square

Crop the source RGBA buffer to a centered square of edge min(w, h). The returned buffer is side * side * 4 bytes. If the input is already square, a copy of the original is returned.