[Mesa-dev] [PATCH 2/2] mesa: Speedup the xrgb -> argb special case in fast_read_rgba_pixels_memcpy

[Martin Andersson]

On Mon, Mar 11, 2013 at 3:56 PM, Jose Fonseca <jfonseca at vmware.com> wrote:
> I'm surprised this is is faster.
>
> In particular, for big things we'll be touching memory twice.
>
> Did you measure the speed up?

I tested it with the previous patch, with GL_UNSIGNED_BYTE, and on
that case it was faster, but since that patch was incorrect (I did not
take endianness into account) this patch can also probably be
discarded.

>
> Jose
>
> ----- Original Message -----
>> ---
>>  src/mesa/main/readpix.c | 5 +++--
>>  1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/src/mesa/main/readpix.c b/src/mesa/main/readpix.c
>> index 349b0bc..0f5c84c 100644
>> --- a/src/mesa/main/readpix.c
>> +++ b/src/mesa/main/readpix.c
>> @@ -285,11 +285,12 @@ fast_read_rgba_pixels_memcpy( struct gl_context *ctx,
>>        }
>>     } else if (copy_xrgb) {
>>        /* convert xrgb -> argb */
>> +      int alphaOffset = texelBytes - 1;
>>        for (j = 0; j < height; j++) {
>> -         GLuint *dst4 = (GLuint *) dst, *map4 = (GLuint *) map;
>> +         memcpy(dst, map, width * texelBytes);
>>           int i;
>>           for (i = 0; i < width; i++) {
>> -            dst4[i] = map4[i] | 0xff000000;  /* set A=0xff */
>> +            dst[i * texelBytes + alphaOffset] = 0xff;  /* set A=0xff */
>>           }
>>           dst += dstStride;
>>           map += stride;
>> --
>> 1.8.1.5
>>
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