[Mesa-dev] [PATCH 01/11] mesa: implement DrawTransformFeedback from ARB_transform_feedback2

[Christoph Bumiller]

On 12/12/2011 05:37 PM, Jose Fonseca wrote:
> ----- Original Message -----
>> On 12/12/2011 02:49 PM, Jose Fonseca wrote:
>>> ----- Original Message -----
>>>> From: Marek Olšák <maraeo at gmail.com>
>>>>
>>>> It's like DrawArrays, but the count is taken from a transform
>>>> feedback
>>>> object.
>>>>
>>>> This removes DrawTransformFeedback from dd_function_table and adds
>>>> the same
>>>> function to GLvertexformat (with the function parameters matching
>>>> GL).
>>>>
>>>> The vbo_draw_func callback has a new parameter
>>>> "struct gl_transform_feedback_object *tfb_vertcount".
>>>>
>>>> The rest of the code just validates states and forwards the
>>>> transform
>>>> feedback object into vbo_draw_func.
>>>
>>> I ventured reviewing this too, and I have a question: the
>>> unfinished code in master had comments saying
>>>
>>>    /*
>>>     * Get number of vertices in obj's feedback buffer.
>>>     * Call ctx->Exec.DrawArrays(mode, 0, count);
>>>     */
>>>
>>> which seems simpler than passing the new tfb_vertcount parameter
>>> everywhere, just for the sake of obtaining count, so what's the
>>> rationale for doing this differently here?
>>>
>>
>> The count is "contained" in the TFB object (through its association
>> with
>> a pipe_stream_output_target which tracks the amount of vertices
>> written
>> to it) and is not supposed to be read back by the CPU because that
>> would
>> mean waiting.
>>
>> The driver will let the GPU write the count into the command buffer,
>> so
>> it only needs to sync command processing with TFB.
> 
> I see. Makes sense.
> 
> I have no more objections against the series FWIW.
> 

Thank you very much for reviewing the changes.

If no one comes along with objections/improvements Marek or I will push
the series in a few days then.

> It would be nice to fix softpipe/llvmpipe though, but IIUC they could not possibly have worked with Mesa before, and I don't think anybody is relying on that softpipe/llvmpipe functionality w/ other state trackers at this point, so I suppose it could wait.
> 
> Jose
>