[Mesa-dev] [PATCH 02/13] mesa: use integers in glReadPixels for GL_RGBA with integer types

[Jordan Justen]

On Tue, Jun 26, 2012 at 2:34 PM, Brian Paul <brianp at vmware.com> wrote:
> On 06/25/2012 06:34 PM, Jordan Justen wrote:
>>
>> Previously if a format of GL_RGBA was used, then float data would
>> be returned, even if the type was an integer type.
>>
>> Signed-off-by: Jordan Justen<jordan.l.justen at intel.com>
>> ---
>>  src/mesa/main/readpix.c |    2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/src/mesa/main/readpix.c b/src/mesa/main/readpix.c
>> index 4058019..e3c4611 100644
>> --- a/src/mesa/main/readpix.c
>> +++ b/src/mesa/main/readpix.c
>> @@ -337,7 +337,7 @@ slow_read_rgba_pixels( struct gl_context *ctx,
>>        goto done;
>>
>>     for (j = 0; j<  height; j++) {
>> -      if (_mesa_is_enum_format_integer(format)) {
>> +      if (_mesa_is_integer_format_or_type(format, type)) {
>>         _mesa_unpack_uint_rgba_row(rbFormat, width, map, (GLuint (*)[4])
>> rgba);
>>           _mesa_rebase_rgba_uint(width, (GLuint (*)[4]) rgba,
>>                                  rb->_BaseFormat);
>
>
> I'm not quite sure I follow this.
>
> If we call glReadPixels(format=GL_RGBA, type=GL_UNSIGNED_BYTE) it looks like
> _mesa_is_integer_format_or_type(format, type) will evaluate to true and
> we'll errantly take the integer path, rather than the float path.
>
> If one wants to read integer-valued colors, you need to pass
> format=GL_RGBA_INTEGER.

This fixed an issue with CopyTexImage and integer clamping.

In meta, we use ReadPixels, and get the base format for the texture,
which for rgb10_a2ui is GL_RGBA.

Should rgb10_a2ui use GL_RGBA_INTEGER for it's base format?

It doesn't look like any gl_format uses an integer base format. Does
this mean that CopyTexImage will always do a int to float conversion
and then a float to int conversion if the src/dest is int based?

Hmm, maybe the issue is that the float path is not clamping integers
properly when re-packing.

I'll investigate further, but any advise would be appreciated.

Thanks for your time,

-Jordan