kc3-lang/angle/src/libANGLE/renderer/metal/QueryMtl.h

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• Hash : 6136cbcb
  Author :
  Date : 2020-09-23T21:31:05
  

  Metal: Implement transform feedback
  
  - XFB is currently emulated by writing to storage buffers.
  
  - Metal doesn't allow vertex shader to both write to storage buffers and
    to stage output (i.e clip position). So if GL_RASTERIZER_DISCARD is
    NOT enabled, the draw with XFB enabled will have 2 passes:
    + First pass: vertex shader writes to XFB buffers + not write to stage
      output + disable rasterizer.
    + Second pass: vertex shader writes to stage output (i.e.
      [[position]]) + enable rasterizer. If GL_RASTERIZER_DISCARD is
      enabled, the second pass is omitted.
    + This effectively executes the same vertex shader twice. TODO:
      possible improvement is writing vertex outputs to buffer in first
      pass then re-use that buffer as input for second pass which has a
      passthrough vertex shader.
  
  - If GL_RASTERIZER_DISCARD is enabled, and XFB is enabled:
    + Only first pass above will be executed, and the render pass will use
      an empty 1x1 texture attachment since rasterization is not needed.
  
  - If GL_RASTERIZER_DISCARD is enabled, but XFB is NOT enabled:
    + we still enable Metal rasterizer.
    + but vertex shader must emulate the discard by writing gl_Position =
      (-3, -3, -3, 1). This effectively moves the vertex out of clip
      space's visible area.
    + This is because GLSL still allows vertex shader to write to stage
      output when rasterizer is disabled. However, Metal doesn't allow
      that. In Metal, if rasterizer is disabled, then vertex shader must
      not write to stage output.
  
  - See src/libANGLE/renderer/metal/doc/TransformFeedback.md for more
    details.
  
  Bug: angleproject:2634
  Change-Id: I6c700e031052560326b7f660ee7597202d38e6aa
  Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2408594
  Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>
  Reviewed-by: Jamie Madill <jmadill@chromium.org>
  Commit-Queue: Jonah Ryan-Davis <jonahr@google.com>
  

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• src/libANGLE/renderer/metal/QueryMtl.h

• //
  // Copyright 2020 The ANGLE Project Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file.
  //
  // QueryMtl.h:
  //    Defines the class interface for QueryMtl, implementing QueryImpl.
  //
  
  #ifndef LIBANGLE_RENDERER_METAL_QUERYMTL_H_
  #define LIBANGLE_RENDERER_METAL_QUERYMTL_H_
  
  #include "libANGLE/renderer/QueryImpl.h"
  #include "libANGLE/renderer/metal/mtl_common.h"
  #include "libANGLE/renderer/metal/mtl_resources.h"
  
  namespace rx
  {
  
  class ContextMtl;
  
  // The class represents offset(s) allocated in the visiblity buffer for an occlusion query.
  // See doc/OcclusionQuery.md.
  // An occlusion query might have more than one offsets allocated, but all of them must be adjacent
  // to each other. Multiple offsets typically allocated when the query is paused and resumed during
  // viewport clear emulation with draw operations. In such case, Metal doesn't allow an offset to
  // be reused in a render pass, hence multiple offsets will be allocated, and their values will
  // be accumulated.
  class VisibilityBufferOffsetsMtl
  {
    public:
      void clear() { mStartOffset = mNumOffsets = 0; }
      bool empty() const { return mNumOffsets == 0; }
      uint32_t size() const { return mNumOffsets; }
  
      // Return last offset
      uint32_t back() const
      {
          ASSERT(!empty());
          return mStartOffset + (mNumOffsets - 1) * mtl::kOcclusionQueryResultSize;
      }
  
      uint32_t front() const
      {
          ASSERT(!empty());
          return mStartOffset;
      }
  
      void setStartOffset(uint32_t offset)
      {
          ASSERT(empty());
          mStartOffset = offset;
          mNumOffsets  = 1;
      }
      void addOffset()
      {
          ASSERT(!empty());
          mNumOffsets++;
      }
  
    private:
      uint32_t mStartOffset = 0;
      uint32_t mNumOffsets  = 0;
  };
  
  class QueryMtl : public QueryImpl
  {
    public:
      QueryMtl(gl::QueryType type);
      ~QueryMtl() override;
  
      void onDestroy(const gl::Context *context) override;
  
      angle::Result begin(const gl::Context *context) override;
      angle::Result end(const gl::Context *context) override;
      angle::Result queryCounter(const gl::Context *context) override;
      angle::Result getResult(const gl::Context *context, GLint *params) override;
      angle::Result getResult(const gl::Context *context, GLuint *params) override;
      angle::Result getResult(const gl::Context *context, GLint64 *params) override;
      angle::Result getResult(const gl::Context *context, GLuint64 *params) override;
      angle::Result isResultAvailable(const gl::Context *context, bool *available) override;
  
      // Get allocated offsets in the render pass's occlusion query pool.
      const VisibilityBufferOffsetsMtl &getAllocatedVisibilityOffsets() const
      {
          return mVisibilityBufferOffsets;
      }
      // Set first allocated offset in the render pass's occlusion query pool.
      void setFirstAllocatedVisibilityOffset(uint32_t off)
      {
          mVisibilityBufferOffsets.setStartOffset(off);
      }
      // Add more offset allocated for the occlusion query
      void addAllocatedVisibilityOffset() { mVisibilityBufferOffsets.addOffset(); }
  
      void clearAllocatedVisibilityOffsets() { mVisibilityBufferOffsets.clear(); }
      // Returns the buffer containing the final occlusion query result.
      const mtl::BufferRef &getVisibilityResultBuffer() const { return mVisibilityResultBuffer; }
      // Reset the occlusion query result stored in buffer to zero
      void resetVisibilityResult(ContextMtl *contextMtl);
  
      void onTransformFeedbackEnd(const gl::Context *context);
  
    private:
      template <typename T>
      angle::Result waitAndGetResult(const gl::Context *context, T *params);
  
      // List of offsets in the render pass's occlusion query pool buffer allocated for this query
      VisibilityBufferOffsetsMtl mVisibilityBufferOffsets;
      mtl::BufferRef mVisibilityResultBuffer;
  
      size_t mTransformFeedbackPrimitivesDrawn = 0;
  };
  
  }  // namespace rx
  
  #endif /* LIBANGLE_RENDERER_METAL_QUERYMTL_H_ */
  

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