[dxvk] Implement transform feedback draw call

src/dxvk/dxvk_buffer.h

@@ -146,6 +146,28 @@ namespace dxvk {
       return prevSlice;
     }
     
+    /**
+     * \brief Transform feedback vertex stride
+     * 
+     * Used when drawing after transform feedback,
+     * \returns The current xfb vertex stride
+     */
+    uint32_t getXfbVertexStride() const {
+      return m_vertexStride;
+    }
+    
+    /**
+     * \brief Set transform feedback vertex stride
+     * 
+     * When the buffer is used as a transform feedback
+     * buffer, this will be set to the vertex stride
+     * defined by the geometry shader.
+     * \param [in] stride Vertex stride
+     */
+    void setXfbVertexStride(uint32_t stride) {
+      m_vertexStride = stride;
+    }
+    
     /**
      * \brief Allocates new physical resource
      * \returns The new backing buffer slice
@@ -171,6 +193,7 @@ namespace dxvk {
     
     DxvkPhysicalBufferSlice m_physSlice;
     uint32_t                m_revision     = 0;
+    uint32_t                m_vertexStride = 0;
     
     sync::Spinlock m_freeMutex;
     sync::Spinlock m_swapMutex;

src/dxvk/dxvk_context.cpp

@@ -1020,6 +1020,25 @@ namespace dxvk {
   }
   
   
+  void DxvkContext::drawIndirectXfb(
+    const DxvkBufferSlice&  counterBuffer,
+          uint32_t          counterDivisor,
+          uint32_t          counterBias) {
+    this->commitGraphicsState();
+
+    if (this->validateGraphicsState()) {
+      auto physicalSlice = counterBuffer.physicalSlice();
+
+      m_cmd->cmdDrawIndirectVertexCount(1, 0,
+        physicalSlice.handle(),
+        physicalSlice.offset(),
+        counterBias, counterDivisor);
+    }
+
+    m_cmd->addStatCtr(DxvkStatCounter::CmdDrawCalls, 1);
+  }
+
+
   void DxvkContext::initImage(
     const Rc<DxvkImage>&           image,
     const VkImageSubresourceRange& subresources) {
@@ -2758,6 +2777,8 @@ namespace dxvk {
   
   
   void DxvkContext::updateTransformFeedbackBuffers() {
+    auto gsOptions = m_state.gp.gs.shader->shaderOptions();
+
     VkBuffer     xfbBuffers[MaxNumXfbBuffers];
     VkDeviceSize xfbOffsets[MaxNumXfbBuffers];
     VkDeviceSize xfbLengths[MaxNumXfbBuffers];
@@ -2772,9 +2793,13 @@ namespace dxvk {
       if (physSlice.handle() == VK_NULL_HANDLE)
         xfbBuffers[i] = m_device->dummyBufferHandle();
       
-      if (physSlice.handle() != VK_NULL_HANDLE)
+      if (physSlice.handle() != VK_NULL_HANDLE) {
+        auto buffer = m_state.xfb.buffers[i].buffer();
+        buffer->setXfbVertexStride(gsOptions.xfbStrides[i]);
+        
         m_cmd->trackResource(physSlice.resource());
       }
+    }
 
     m_cmd->cmdBindTransformFeedbackBuffers(
       0, MaxNumXfbBuffers,

src/dxvk/dxvk_context.h

@@ -486,6 +486,18 @@ namespace dxvk {
             uint32_t          count,
             uint32_t          stride);
     
+    /**
+     * \brief Transform feddback draw call
+
+     * \param [in] counterBuffer Xfb counter buffer
+     * \param [in] counterDivisor Vertex stride
+     * \param [in] counterBias Counter bias
+     */
+    void drawIndirectXfb(
+      const DxvkBufferSlice&  counterBuffer,
+            uint32_t          counterDivisor,
+            uint32_t          counterBias);
+    
     /**
      * \brief Generates mip maps
      *