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

[Brian Paul]

On 03/24/2014 02:52 AM, Kenneth Graunke wrote:
> 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;
>               }
>            }
>

I still think a comment on the new function would be nice.  Looks good 
though.

Reviewed-by: Brian Paul <brianp at vmware.com>