Add an option for the draw batcher to collect vertex shader output. Disabled by default.

src/xenia/gpu/gl4/draw_batcher.cc

@@ -48,13 +48,92 @@ bool DrawBatcher::Initialize(CircularBuffer* array_data_buffer) {
   if (!state_buffer_.Initialize()) {
     return false;
   }
+  if (!InitializeTFB()) {
+    return false;
+  }
+
   glBindBuffer(GL_DRAW_INDIRECT_BUFFER, command_buffer_.handle());
   return true;
 }
 
+// Initializes a transform feedback object
+// We use this to capture vertex data straight from the vertex/geometry shader.
+bool DrawBatcher::InitializeTFB() {
+  glGenBuffers(1, &tfvbo_);
+  if (!tfvbo_) {
+    return false;
+  }
+
+  glGenTransformFeedbacks(1, &tfbo_);
+  if (!tfbo_) {
+    return false;
+  }
+
+  glGenQueries(1, &tfqo_);
+  if (!tfqo_) {
+    return false;
+  }
+
+  // TODO(DrChat): Calculate this based on the number of primitives drawn.
+  glBindBuffer(GL_ARRAY_BUFFER, tfvbo_);
+  glBufferData(GL_ARRAY_BUFFER, 16384 * 4, nullptr, GL_STATIC_READ);
+  glBindBuffer(GL_ARRAY_BUFFER, 0);
+
+  return true;
+}
+
+void DrawBatcher::ShutdownTFB() {
+  glDeleteBuffers(1, &tfvbo_);
+  glDeleteTransformFeedbacks(1, &tfbo_);
+  glDeleteQueries(1, &tfqo_);
+
+  tfvbo_ = 0;
+  tfbo_ = 0;
+  tfqo_ = 0;
+}
+
+size_t DrawBatcher::QueryTFBSize() {
+  if (!tfb_enabled_) {
+    return 0;
+  }
+
+  size_t size = 0;
+  switch (tfb_prim_type_gl_) {
+    case GL_POINTS:
+      size = tfb_prim_count_ * 1 * 4 * 4;
+      break;
+    case GL_LINES:
+      size = tfb_prim_count_ * 2 * 4 * 4;
+      break;
+    case GL_TRIANGLES:
+      size = tfb_prim_count_ * 3 * 4 * 4;
+      break;
+  }
+
+  return size;
+}
+
+bool DrawBatcher::ReadbackTFB(void* buffer, size_t size) {
+  if (!tfb_enabled_) {
+    XELOGW("DrawBatcher::ReadbackTFB called when TFB was disabled!");
+    return false;
+  }
+
+  glBindBuffer(GL_ARRAY_BUFFER, tfvbo_);
+  void* data = glMapBufferRange(GL_ARRAY_BUFFER, 0, size, GL_MAP_READ_BIT);
+
+  std::memcpy(buffer, data, size);
+
+  glUnmapBuffer(GL_ARRAY_BUFFER);
+  glBindBuffer(GL_ARRAY_BUFFER, 0);
+
+  return true;
+}
+
 void DrawBatcher::Shutdown() {
   command_buffer_.Shutdown();
   state_buffer_.Shutdown();
+  ShutdownTFB();
 }
 
 bool DrawBatcher::ReconfigurePipeline(GL4Shader* vertex_shader,
@@ -242,6 +321,84 @@ bool DrawBatcher::CommitDraw() {
   return true;
 }
 
+void DrawBatcher::TFBBegin(PrimitiveType prim_type) {
+  if (!tfb_enabled_) {
+    return;
+  }
+
+  // Translate the primitive typename to something compatible with TFB.
+  GLenum gl_prim_type = 0;
+  switch (prim_type) {
+    case PrimitiveType::kLineList:
+      gl_prim_type = GL_LINES;
+      break;
+    case PrimitiveType::kLineStrip:
+      gl_prim_type = GL_LINES;
+      break;
+    case PrimitiveType::kLineLoop:
+      gl_prim_type = GL_LINES;
+      break;
+    case PrimitiveType::kPointList:
+      // The geometry shader associated with this writes out triangles.
+      gl_prim_type = GL_TRIANGLES;
+      break;
+    case PrimitiveType::kTriangleList:
+      gl_prim_type = GL_TRIANGLES;
+      break;
+    case PrimitiveType::kTriangleStrip:
+      gl_prim_type = GL_TRIANGLES;
+      break;
+    case PrimitiveType::kRectangleList:
+      gl_prim_type = GL_TRIANGLES;
+      break;
+    case PrimitiveType::kTriangleFan:
+      gl_prim_type = GL_TRIANGLES;
+      break;
+    case PrimitiveType::kQuadList:
+      // FIXME: In some cases the geometry shader will output lines.
+      // See: GL4CommandProcessor::UpdateShaders
+      gl_prim_type = GL_TRIANGLES;
+      break;
+    default:
+      assert_unhandled_case(prim_type);
+      break;
+  }
+
+  // TODO(DrChat): Resize the TFVBO here.
+  // Could draw a 2nd time with the rasterizer disabled once we have a primitive
+  // count.
+
+  tfb_prim_type_ = prim_type;
+  tfb_prim_type_gl_ = gl_prim_type;
+
+  glBindTransformFeedback(GL_TRANSFORM_FEEDBACK, tfbo_);
+
+  // Bind the buffer to the TFB object.
+  glBindBufferBase(GL_TRANSFORM_FEEDBACK_BUFFER, 0, tfvbo_);
+
+  // Begin a query for # prims written
+  glBeginQueryIndexed(GL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN, 0, tfqo_);
+
+  // Begin capturing.
+  glBeginTransformFeedback(gl_prim_type);
+}
+
+void DrawBatcher::TFBEnd() {
+  if (!tfb_enabled_) {
+    return;
+  }
+
+  glEndTransformFeedback();
+  glEndQueryIndexed(GL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN, 0);
+  glBindBufferBase(GL_TRANSFORM_FEEDBACK_BUFFER, 0, 0);
+  glBindTransformFeedback(GL_TRANSFORM_FEEDBACK, 0);
+
+  // Cache the query size as query objects aren't shared.
+  GLint prim_count = 0;
+  glGetQueryObjectiv(tfqo_, GL_QUERY_RESULT, &prim_count);
+  tfb_prim_count_ = prim_count;
+}
+
 bool DrawBatcher::Flush(FlushMode mode) {
   GLboolean cull_enabled = 0;
   if (batch_state_.draw_count) {
@@ -263,6 +420,7 @@ bool DrawBatcher::Flush(FlushMode mode) {
                       batch_state_.state_range_length);
 
     GLenum prim_type = 0;
+    bool valid_prim = true;
     switch (batch_state_.prim_type) {
       case PrimitiveType::kPointList:
         prim_type = GL_POINTS;
@@ -291,8 +449,6 @@ bool DrawBatcher::Flush(FlushMode mode) {
         // assert_true(
         // (register_file_->values[XE_GPU_REG_PA_SU_SC_MODE_CNTL].u32
         // & 0x3) == 0);
-        cull_enabled = glIsEnabled(GL_CULL_FACE);
-        glDisable(GL_CULL_FACE);
         break;
       case PrimitiveType::kQuadList:
         prim_type = GL_LINES_ADJACENCY;
@@ -300,17 +456,21 @@ bool DrawBatcher::Flush(FlushMode mode) {
       default:
       case PrimitiveType::kUnknown0x07:
         prim_type = GL_POINTS;
+        valid_prim = false;
         XELOGE("unsupported primitive type %d", batch_state_.prim_type);
         assert_unhandled_case(batch_state_.prim_type);
-        DiscardDraw();
-        return false;
+        break;
     }
 
     // Fast path for single draws.
     void* indirect_offset =
         reinterpret_cast<void*>(batch_state_.command_range_start);
 
-    if (batch_state_.draw_count == 1) {
+    if (tfb_enabled_) {
+      TFBBegin(batch_state_.prim_type);
+    }
+
+    if (valid_prim && batch_state_.draw_count == 1) {
       // Fast path for one draw. Removes MDI overhead when not required.
       if (batch_state_.indexed) {
         auto& cmd = active_draw_.draw_elements_cmd;
@@ -326,7 +486,7 @@ bool DrawBatcher::Flush(FlushMode mode) {
                                           cmd->count, cmd->instance_count,
                                           cmd->base_instance);
       }
-    } else {
+    } else if (valid_prim) {
       // Full multi-draw.
       if (batch_state_.indexed) {
         glMultiDrawElementsIndirect(prim_type, batch_state_.index_type,
@@ -339,6 +499,10 @@ bool DrawBatcher::Flush(FlushMode mode) {
       }
     }
 
+    if (tfb_enabled_) {
+      TFBEnd();
+    }
+
     batch_state_.command_range_start = UINTPTR_MAX;
     batch_state_.command_range_length = 0;
     batch_state_.state_range_start = UINTPTR_MAX;
@@ -346,10 +510,6 @@ bool DrawBatcher::Flush(FlushMode mode) {
     batch_state_.draw_count = 0;
   }
 
-  if (batch_state_.prim_type == PrimitiveType::kRectangleList && cull_enabled) {
-    glEnable(GL_CULL_FACE);
-  }
-
   if (mode == FlushMode::kReconfigure) {
     // Reset - we'll update it as soon as we have all the information.
     batch_state_.needs_reconfigure = true;

src/xenia/gpu/gl4/draw_batcher.h

@@ -99,7 +99,21 @@ class DrawBatcher {
   bool CommitDraw();
   bool Flush(FlushMode mode);
 
+  // TFB - Filled with vertex shader output from the last flush.
+  size_t QueryTFBSize();
+  bool ReadbackTFB(void* buffer, size_t size);
+
+  GLuint tfvbo() { return tfvbo_; }
+  bool is_tfb_enabled() const { return tfb_enabled_; }
+  void set_tfb_enabled(bool enabled) { tfb_enabled_ = enabled; }
+
  private:
+  bool InitializeTFB();
+  void ShutdownTFB();
+
+  void TFBBegin(PrimitiveType prim_type);
+  void TFBEnd();
+
   bool BeginDraw();
   void CopyConstants();
 
@@ -108,6 +122,14 @@ class DrawBatcher {
   CircularBuffer state_buffer_;
   CircularBuffer* array_data_buffer_;
 
+  GLuint tfbo_ = 0;
+  GLuint tfvbo_ = 0;
+  GLuint tfqo_ = 0;
+  PrimitiveType tfb_prim_type_ = PrimitiveType::kNone;
+  GLenum tfb_prim_type_gl_ = 0;
+  GLint tfb_prim_count_ = 0;
+  bool tfb_enabled_ = false;
+
   struct BatchState {
     bool needs_reconfigure;
     PrimitiveType prim_type;