[Impeller] In advanced blends, unpremultiply and apply src_input_alpha only if there is no foreground color#50260
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| v_src_texture_coords // texture coordinates | ||
| )); | ||
| src *= blend_info.src_input_alpha; | ||
| )) * blend_info.src_input_alpha; |
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When applying blend_info.src_input_alpha to an unpremultiplied color, only the a component should be adjusted, otherwise the color components will become darker as it becomes more transparent.
| f16vec4 src = IPHalfUnpremultiply( | ||
| f16vec4 src = | ||
| blend_info.color_factor > 0.0hf | ||
| ? blend_info.color |
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This change makes sense... this color never gets premultiplied on the CPU side before we get here. Could you add a comment saying this color is expected to be unpremultiplied in the shader struct where it's defined?
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That comment already exists:
https://github.com/flutter/engine/blob/main/impeller/entity/shaders/blending/advanced_blend.frag#L18
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…a only if there is no foreground color See flutter/flutter#142620
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…put_alpha only if there is no foreground color (flutter/engine#50260)
flutter/engine@fee0214...23763db 2024-02-03 [email protected] [Impeller] Fix blown stack due to always out of date window dimensions on high-dpi devices. (flutter/engine#50307) 2024-02-02 [email protected] [Impeller] In advanced blends, unpremultiply and apply src_input_alpha only if there is no foreground color (flutter/engine#50260) 2024-02-02 [email protected] [Impeller] new blur: clamp downsample scalar to 1/16 (flutter/engine#50262) If this roll has caused a breakage, revert this CL and stop the roller using the controls here: https://autoroll.skia.org/r/flutter-engine-flutter-autoroll Please CC [email protected],[email protected],[email protected] on the revert to ensure that a human is aware of the problem. To file a bug in Flutter: https://github.com/flutter/flutter/issues/new/choose To report a problem with the AutoRoller itself, please file a bug: https://issues.skia.org/issues/new?component=1389291&template=1850622 Documentation for the AutoRoller is here: https://skia.googlesource.com/buildbot/+doc/main/autoroll/README.md
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See flutter/flutter#142620