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fix(wuffs): don't premul alpha when loading png (#5189)

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This was causing excessively faint/dark areas anywhere there was
transparency, since our image shaders for both Metal and OpenGL assume
the image data has straight alpha (which, I think should be the case for
data transmitted directly with kitty graphics protocol rather than
png-encoded), and do an additional multiplication.

After this change, our image blending looks *like most other apps*, even
though it's still technically wrong since it "should" be done in linear
space. Kitty, for example, does do linear blending for images, which is
*more correct* even though it doesn't look like most apps. On macOS if
`text-blending` is set to `linear` we do get linear blending, and match
Kitty exactly with this change.

In order to have linear blending of images while maintaining non-linear
blending of text for a "native" look on macOS we'd have to use swap
textures with different pixel formats (`*_srgb` / not `*_srgb`) or else
the API validator yells at us (even though it *does* work correctly...)
-- either that or perform our blending in a shader instead of relying on
Metal, which is my plan ultimately whenever I get around to making the
deferred render pipeline.
This commit is contained in:
Mitchell Hashimoto
2025-01-20 10:22:10 -08:00
committed by GitHub
parent 07d5ae749d c2da843dfd
commit 0eb6f28375
2 changed files with 2 additions and 22 deletions
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12
pkg/wuffs/src/jpeg.zig
View File

@ -55,7 +55,7 @@ pub fn decode(alloc: Allocator, data: []const u8) Error!ImageData {
c.wuffs_base__pixel_config__set(
&image_config.pixcfg,
c.WUFFS_BASE__PIXEL_FORMAT__RGBA_PREMUL,
c.WUFFS_BASE__PIXEL_FORMAT__RGBA_NONPREMUL,
c.WUFFS_BASE__PIXEL_SUBSAMPLING__NONE,
width,
height,
@ -95,16 +95,6 @@ pub fn decode(alloc: Allocator, data: []const u8) Error!ImageData {
try check(log, &status);
}
var frame_config: c.wuffs_base__frame_config = undefined;
{
const status = c.wuffs_jpeg__decoder__decode_frame_config(
decoder,
&frame_config,
&source_buffer,
);
try check(log, &status);
}
{
const status = c.wuffs_jpeg__decoder__decode_frame(
decoder,

12
pkg/wuffs/src/png.zig
View File

@ -55,7 +55,7 @@ pub fn decode(alloc: Allocator, data: []const u8) Error!ImageData {
c.wuffs_base__pixel_config__set(
&image_config.pixcfg,
c.WUFFS_BASE__PIXEL_FORMAT__RGBA_PREMUL,
c.WUFFS_BASE__PIXEL_FORMAT__RGBA_NONPREMUL,
c.WUFFS_BASE__PIXEL_SUBSAMPLING__NONE,
width,
height,
@ -95,16 +95,6 @@ pub fn decode(alloc: Allocator, data: []const u8) Error!ImageData {
try check(log, &status);
}
var frame_config: c.wuffs_base__frame_config = undefined;
{
const status = c.wuffs_png__decoder__decode_frame_config(
decoder,
&frame_config,
&source_buffer,
);
try check(log, &status);
}
{
const status = c.wuffs_png__decoder__decode_frame(
decoder,