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[Fix] (DirectGLES): report the alpha added by the multisample widening as ONE

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A three-channel format widened to four for a multisample target gains an alpha
channel the application never asked for, and it holds whatever the draw that filled
the texture happened to write there. GL says a format without alpha reads back as
1.0, so KHR-GL33.texture_swizzle - which fills such a texture by rendering
vec4(r, g, b, 0.0) and then swizzles red from alpha - read 0 where it expected the
maximum.

Fold ONE into the texture's swizzle for exactly those textures, composed with the
swizzle the application set, so the promotion stays invisible.
This commit is contained in:
BZLZHH
2026-08-02 04:25:08 -04:00
parent e45f7ae5d4
commit 01d0f01d13
3 changed files with 34 additions and 1 deletions
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MobileGL/MG_Backend/DirectGLES/Utils.h
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@@ -40,6 +40,11 @@ namespace MobileGL::MG_Backend::DirectGLES {
void GenerateRenderbufferFormatInfo(TextureInternalFormat internalFormat, GLenum* outInternalFormat,
GLenum* outFormat, GLenum* outType);
Bool ShouldUseCaveatTextureFormat(TextureInternalFormat internalFormat, TextureTarget target);
// True when the format the texture is actually created with has an alpha channel the
// frontend format does not (the three-channel multisample widening). GL reads such a
// channel back as 1.0, so any swizzle source of ALPHA has to be answered with ONE.
Bool BackendTextureFormatAddsAlpha(TextureInternalFormat internalFormat, TextureTarget target);
Bool ShouldUseCaveatRenderbufferFormat(TextureInternalFormat internalFormat);
} // namespace TextureImpl