Hi Andreas, On Sun, 25 Aug 2019 at 21:11, Andreas Bergmeier <abergme...@gmx.net> wrote: > For a few weeks now I am working on implementing Vulkan for VideoCore 6 AKA > 42 (using V3D/DRM). Don't hold you breath ;)
Great! I can't say much about the specifics of VideoCore hardware, but at least for some of the common parts ... > Currently I am trying to understand what is necessary or how to interact with > V3D. So I am looking at TransformFeedback because it interacts with quite a > few other parts of the pipeline and still seems less mangled into the big > logic than other features. So I am comparing how Gallium (V3D) is handling TF > in the state tracker VS how Vulkan (Intel) is handling the Extension. > > The following is what I so far think I gathered: > 1. GV3D is handling TransformFeedback directly with other bound parts of the > pipeline (e.g. `emit_state` in _v3dx_emit.c_). It seems to look into the > shader and associated TF specs. It seems to use "streamout targets", although > I do not yet understand what these are really. Then it passes all the > offsets, indices and finally resources to V3D. 'Stream out' is basically just what DirectX calls its version of transform feedback. The idea is the same: capturing output from vertex/geometry stages. > 2. The Vulkan Extension only knows about CounterBuffers and iterates over > these. Intel seems to call TF -> XF? and subsequently the buffers XFB. Have > also not yet gathered what is the difference and what all the gazillion > acronyms mean. 'XFB' is the most widely-used acronym for transform, as 'trans' or 'cross' can abbreviate to X. 'TF' is not as widely used as XFB. > So far my idea would be to implement TF similar to Intel and instead of > iterating over "streamout targets" I would iterate XFBs. So these would really be the same thing. A streamout target is where the VC4 writes its output stream of data from these shading stages, and a counter buffer is where Vulkan writes the output stream of data from these shading stages. > The problem with this approach is, that it will not be easy to mimic > `cl_emit` calls similar to Gallium. > My question now is which parts of V3D emits have a dependency. > > I would assume that I can move TRANSFORM_FEEDBACK_SPECS and > TRANSFORM_FEEDBACK_ENABLE to cmd state flush in Vulkan. > `vkCmdBeginTransformFeedbackEXT` shoudl then only need > TRANSFORM_FEEDBACK_BUFFER and TRANSFORM_FEEDBACK_OUTPUT_ADDRESS. > > Sorry if this is a bit confusing - I am really just trying to figure this out > one by one. This is getting more into the specifics of how you've structured the driver, as well as hardware specifics, but it sounds about right to me. Cheers, Daniel _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/mesa-dev
