> >> 2. How do you pass to Gallium the id parameter to DrawTransformFeedback? > > You bind the buffer with the given id before issuing draw_stream_output. Bind to what? Note that the id parameter to DrawTransformFeedback is _not_ the place to write to stream output to, but the place to take the count of primitives to draw from. That's because there is one count for each transform feedback object in GL, not just a per-context one like in D3D10, and you pass the one you want to use as the amount of primitives to draw to DrawTransformFeedback (and if desired you use BindTransformFeedback to choose the one to use for writing, which is unrelated).
>> 3. How do you handle pause/resume in ARB_transform_feedback2? (it must >> _not_ reset the count) > > You just append to the buffer. > You do not append to the buffer =) OK, but how do you tell the GPU to start writing from 0 and reset the count in some cases, and to append and not reset the count in the others? For instance in GL you can pause a transform feedback object, bind some other object, then resume the first, and it must start where it left off. In general, the OpenGL semantics are much more complex and need a more powerful Gallium interface than the D3D10 ones. > The question is "how much data is in this pipe_buffer" so you hold that in the > pipe_buffer itself. No, the question is "how many primitives were streamed out when that transform feedback object was bound to GL and not paused between the last Begin and End GL calls?". Or more precisely, how to design a Gallium interface that can express that. > You hold the size of the buffer in the buffer and different so objects do > whatever they want (append, rewrite,...) As far as I can tell in OpenGL each transform feedback object has its own count and several transform feedback objects can have the same buffer bound, so you can't associate the primitive count to the buffer. Anyway, trying to implement ARB_transform_feedback2 (or, better, ARB_transform_feedback3) will quickly show the requirements for the Gallium interface. _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
