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glamor: Don't override source alpha to 1.0 if it's used for blending

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It caused an incorrect result of the blend operation.

Use glColorMask to prevent non-1.0 alpha channel values in a depth 32
pixmap backing an effective depth 24 window. For blending operations,
the expectation is that the destination drawable contains valid pixel
values, so the alpha channel should already be 1.0.

Fixes: d1f142891e ("glamor: Ignore destination alpha as necessary for composite operation")
Issue: https://gitlab.gnome.org/GNOME/mutter/-/issues/3104
(cherry picked from commit d1bbf82d72)
This commit is contained in:
Michel Dänzer 2024-01-05 18:31:11 +01:00 • committed by Olivier Fourdan
parent 7b3010b26d
commit 02236e3fda
1 changed files with 27 additions and 1 deletions
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28
glamor/glamor_render.c
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@ -834,6 +834,20 @@ glamor_render_format_is_supported(PicturePtr picture)
}
}
static Bool
render_op_uses_src_alpha(CARD8 op)
{
struct blendinfo *info = &composite_op_info[op];
switch (info->dest_blend) {
case GL_ONE_MINUS_SRC_ALPHA:
case GL_SRC_ALPHA:
return TRUE;
}
return FALSE;
}
static Bool
glamor_composite_choose_shader(CARD8 op,
PicturePtr source,
@ -947,7 +961,8 @@ glamor_composite_choose_shader(CARD8 op,
key.dest_swizzle = SHADER_DEST_SWIZZLE_ALPHA_TO_RED;
} else {
if (dest_pixmap->drawable.depth == 32 &&
glamor_drawable_effective_depth(dest->pDrawable) == 24)
glamor_drawable_effective_depth(dest->pDrawable) == 24 &&
!render_op_uses_src_alpha(op))
key.dest_swizzle = SHADER_DEST_SWIZZLE_IGNORE_ALPHA;
else
key.dest_swizzle = SHADER_DEST_SWIZZLE_DEFAULT;
@ -1181,6 +1196,7 @@ glamor_composite_with_shader(CARD8 op,
Bool ret = FALSE;
glamor_composite_shader *shader = NULL, *shader_ca = NULL;
struct blendinfo op_info, op_info_ca;
Bool restore_colormask = FALSE;
if (!glamor_composite_choose_shader(op, source, mask, dest,
source_pixmap, mask_pixmap, dest_pixmap,
@ -1205,6 +1221,14 @@ glamor_composite_with_shader(CARD8 op,
glamor_make_current(glamor_priv);
if (ca_state != CA_TWO_PASS &&
key.dest_swizzle == SHADER_DEST_SWIZZLE_DEFAULT &&
dest_pixmap->drawable.depth == 32 &&
glamor_drawable_effective_depth(dest->pDrawable) == 24) {
glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_FALSE);
restore_colormask = TRUE;
}
glamor_set_destination_pixmap_priv_nc(glamor_priv, dest_pixmap, dest_pixmap_priv);
glamor_composite_set_shader_blend(glamor_priv, dest_pixmap_priv, &key, shader, &op_info);
glamor_set_alu(screen, GXcopy);
@ -1347,6 +1371,8 @@ glamor_composite_with_shader(CARD8 op,
glDisable(GL_SCISSOR_TEST);
disable_va:
if (restore_colormask)
glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
glDisableVertexAttribArray(GLAMOR_VERTEX_POS);
glDisableVertexAttribArray(GLAMOR_VERTEX_SOURCE);
glDisableVertexAttribArray(GLAMOR_VERTEX_MASK);