[Mesa-dev] [PATCH 2/3] mesa: Skip clearing color buffers when color writes are disabled.

[Kenneth Graunke]

WebGL Aquarium in Chrome 24 actually hits this.

v2: Move to core Mesa (wisely suggested by Ian); only consider
    components which actually exist.

v3: Use _mesa_format_has_color_component to determine whether components
    actually exist, fixing alpha format handling.

Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
---
 src/mesa/main/clear.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

Thanks for the review!  You're absolutely right about ALPHA formats.

I think this version should actually work :)

diff --git a/src/mesa/main/clear.c b/src/mesa/main/clear.c
index 077c5fc..e2566c0 100644
--- a/src/mesa/main/clear.c
+++ b/src/mesa/main/clear.c
@@ -106,6 +106,24 @@ _mesa_ClearColorIuiEXT(GLuint r, GLuint g, GLuint b, GLuint a)
 }
 
 
+static bool
+color_buffer_writes_enabled(const struct gl_context *ctx, unsigned idx)
+{
+   struct gl_renderbuffer *rb = ctx->DrawBuffer->_ColorDrawBuffers[idx];
+   GLuint c;
+   GLubyte colorMask = 0;
+
+   if (rb) {
+      for (c = 0; c < 4; c++) {
+         if (_mesa_format_has_color_component(rb->Format, c))
+            colorMask |= ctx->Color.ColorMask[idx][c];
+      }
+   }
+
+   return colorMask != 0;
+}
+
+
 /**
  * Clear buffers.
  * 
@@ -181,7 +199,7 @@ _mesa_Clear( GLbitfield mask )
          for (i = 0; i < ctx->DrawBuffer->_NumColorDrawBuffers; i++) {
             GLint buf = ctx->DrawBuffer->_ColorDrawBufferIndexes[i];
 
-            if (buf >= 0) {
+            if (buf >= 0 && color_buffer_writes_enabled(ctx, i)) {
                bufferMask |= 1 << buf;
             }
          }
-- 
1.9.0