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

[Marek Olšák]

The format can also be luminance or intensity.

Marek

On Sat, Mar 22, 2014 at 5:18 PM, Brian Paul <brianp at vmware.com> wrote:
> On 03/21/2014 05:22 PM, 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.
>>
>> Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
>> Cc: Ian Romanick <idr at freedesktop.org>
>> Cc: Paul Berry <stereotype441 at gmail.com>
>> Cc: Anuj Phogat <anuj.phogat at gmail.com>
>> ---
>>   src/mesa/main/clear.c | 19 ++++++++++++++++++-
>>   1 file changed, 18 insertions(+), 1 deletion(-)
>>
>> Good call, Ian!  I was a bit sleepy last night when I wrote that code :)
>>
>> Here's an updated patch which moves it to core Mesa.  It also only checks
>> the writemask of enabled components.
>>
>> I didn't see any existing code to handle this.  There's similar code which
>> disables depth clears if Depth.Mask == 0, but I didn't see any for color.
>>
>> diff --git a/src/mesa/main/clear.c b/src/mesa/main/clear.c
>> index 077c5fc..c9ca681 100644
>> --- a/src/mesa/main/clear.c
>> +++ b/src/mesa/main/clear.c
>> @@ -106,6 +106,23 @@ _mesa_ClearColorIuiEXT(GLuint r, GLuint g, GLuint b,
>> GLuint a)
>>   }
>>
>>
>
> Could you add a comment to the function to explain it?
>
> What if the buffer is a GL_ALPHA only buffer (I think that's possible)?
> Then _mesa_format_num_components() would be one and we should check the
> colormask's A component, right?
>
>
>
>
>> +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 < _mesa_format_num_components(rb->Format); c++) {
>> +         colorMask |= ctx->Color.ColorMask[idx][c];
>> +      }
>> +   }
>> +
>> +   return colorMask != 0;
>> +}
>> +
>> +
>>   /**
>>    * Clear buffers.
>>    *
>> @@ -181,7 +198,7 @@ _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;
>>               }
>>            }
>>
>
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