When faking an RGB format with an RGBA format, there may be a channel
of data containing garbage. st/mesa already overrides texture swizzles
to replace the A channel with ONE. This patch makes it override blend
factors to achieve a similar effect.
It appears that st_update_blend is already called when the framebuffer
is changed, so it should be safe to look at the render target formats
without adding additional state dependencies.
---
src/mesa/state_tracker/st_atom_blend.c | 35 ++++++++++++++++++++++++++
1 file changed, 35 insertions(+)
diff --git a/src/mesa/state_tracker/st_atom_blend.c
b/src/mesa/state_tracker/st_atom_blend.c
index 804de2f154f..3e6e4411107 100644
--- a/src/mesa/state_tracker/st_atom_blend.c
+++ b/src/mesa/state_tracker/st_atom_blend.c
@@ -41,6 +41,7 @@
#include "framebuffer.h"
#include "main/blend.h"
+#include "main/glformats.h"
#include "main/macros.h"
/**
@@ -142,6 +143,28 @@ blend_per_rt(const struct gl_context *ctx, unsigned num_cb)
return GL_FALSE;
}
+/**
+ * Modify blend function to force destination alpha to 1.0
+ *
+ * If \c function specifies a blend function that uses destination alpha,
+ * replace it with a function that hard-wires destination alpha to 1.0. This
+ * is used when rendering to xRGB targets.
+ */
+static enum pipe_blendfactor
+fix_xrgb_alpha(enum pipe_blendfactor factor)
+{
+ switch (factor) {
+ case PIPE_BLENDFACTOR_DST_ALPHA:
+ return PIPE_BLENDFACTOR_ONE;
+
+ case PIPE_BLENDFACTOR_INV_DST_ALPHA:
+ case PIPE_BLENDFACTOR_SRC_ALPHA_SATURATE:
+ return PIPE_BLENDFACTOR_ZERO;
+ default:
+ return factor;
+ }
+}
+
void
st_update_blend( struct st_context *st )
{
@@ -210,6 +233,18 @@ st_update_blend( struct st_context *st )
blend->rt[i].alpha_dst_factor =
translate_blend(ctx->Color.Blend[j].DstA);
}
+
+ const struct gl_renderbuffer *rb =
+ ctx->DrawBuffer->_ColorDrawBuffers[i];
+
+ if (rb && !_mesa_base_format_has_channel(rb->_BaseFormat,
+ GL_TEXTURE_ALPHA_TYPE)) {
+ struct pipe_rt_blend_state *rt = &blend->rt[i];
+ rt->rgb_src_factor = fix_xrgb_alpha(rt->rgb_src_factor);
+ rt->rgb_dst_factor = fix_xrgb_alpha(rt->rgb_dst_factor);
+ rt->alpha_src_factor = fix_xrgb_alpha(rt->alpha_src_factor);
+ rt->alpha_dst_factor = fix_xrgb_alpha(rt->alpha_dst_factor);
+ }
}
}
else {
--
2.18.0
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