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Rename AlphaFromCoverage to FontColorTransferFunction (#8201)

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`ab_glyph` would output coverage values, but `vello` outputs RGBA. So
the old name was a misnomer.

I also suspect our default values are wrong, but I need to investigate
that more properly in a separate PR.
This commit is contained in:
Emil Ernerfeldt
2026-05-26 10:51:39 +02:00
committed by GitHub
parent 71f22ff1a5
commit fc1b2a99fd
6 changed files with 113 additions and 58 deletions
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30
crates/epaint/src/text/font.rs
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@@ -1,5 +1,6 @@
#![expect(clippy::mem_forget)]
use ecolor::Color32;
use emath::{GuiRounding as _, OrderedFloat, Vec2, vec2};
use self_cell::self_cell;
use skrifa::{GlyphId, MetadataProvider as _};
@@ -274,26 +275,31 @@ impl FontCell {
let width = bounds.width() as u16;
let height = bounds.height() as u16;
let mut ctx = vello_cpu::RenderContext::new(width, height);
ctx.set_transform(kurbo::Affine::translate((-bounds.x0, -bounds.y0)));
ctx.set_paint(color::OpaqueColor::<color::Srgb>::WHITE);
ctx.fill_path(&path);
let mut dest = vello_cpu::Pixmap::new(width, height);
let mut resources = vello_cpu::Resources::new();
ctx.render_to_pixmap(&mut resources, &mut dest);
let uv_rect = if width == 0 || height == 0 {
UvRect::default()
} else {
let mut ctx = vello_cpu::RenderContext::new(width, height);
ctx.set_transform(kurbo::Affine::translate((-bounds.x0, -bounds.y0)));
ctx.set_paint(color::OpaqueColor::<color::Srgb>::WHITE);
ctx.fill_path(&path);
let mut dest = vello_cpu::Pixmap::new(width, height);
let mut resources = vello_cpu::Resources::new();
ctx.render_to_pixmap(&mut resources, &mut dest);
let glyph_pos = {
let alpha_from_coverage = atlas.options().alpha_from_coverage;
let color_transfer_function = atlas.options().color_transfer_function;
let (glyph_pos, image) = atlas.allocate((width as usize, height as usize));
let pixels = dest.data_as_u8_slice();
for y in 0..height as usize {
for x in 0..width as usize {
image[(x + glyph_pos.0, y + glyph_pos.1)] = alpha_from_coverage
.color_from_coverage(
pixels[((y * width as usize) + x) * 4 + 3] as f32 / 255.0,
);
let pixel_offset = 4 * ((y * width as usize) + x);
image[(x + glyph_pos.0, y + glyph_pos.1)] = color_transfer_function
.to_atlas_color(Color32::from_rgba_premultiplied(
pixels[pixel_offset],
pixels[pixel_offset + 1],
pixels[pixel_offset + 2],
pixels[pixel_offset + 3],
));
}
}
glyph_pos