[dxvk] Skip draws if no index buffer is bound

It doesn't make much sense to bind the null buffer here, as we'd
just draw the same vertex over and over again.

src/dxvk/dxvk_context.cpp

@@ -4117,24 +4117,22 @@ namespace dxvk {
   }
   
   
-  void DxvkContext::updateIndexBufferBinding() {
-    m_flags.clr(DxvkContextFlag::GpDirtyIndexBuffer);
-    
-    if (m_state.vi.indexBuffer.defined()) {
-      auto bufferInfo = m_state.vi.indexBuffer.getDescriptor();
-      
-      m_cmd->cmdBindIndexBuffer(
-        bufferInfo.buffer.buffer,
-        bufferInfo.buffer.offset,
-        m_state.vi.indexType);
+  bool DxvkContext::updateIndexBufferBinding() {
+    if (unlikely(!m_state.vi.indexBuffer.defined()))
+      return false;
 
-      if (m_vbTracked.set(MaxNumVertexBindings))
-        m_cmd->trackResource<DxvkAccess::Read>(m_state.vi.indexBuffer.buffer());
-    } else {
-      m_cmd->cmdBindIndexBuffer(
-        m_common->dummyResources().bufferHandle(),
-        0, VK_INDEX_TYPE_UINT32);
-    }
+    m_flags.clr(DxvkContextFlag::GpDirtyIndexBuffer);
+    auto bufferInfo = m_state.vi.indexBuffer.getDescriptor();
+
+    m_cmd->cmdBindIndexBuffer(
+      bufferInfo.buffer.buffer,
+      bufferInfo.buffer.offset,
+      m_state.vi.indexType);
+
+    if (m_vbTracked.set(MaxNumVertexBindings))
+      m_cmd->trackResource<DxvkAccess::Read>(m_state.vi.indexBuffer.buffer());
+
+    return true;
   }
   
   
@@ -4346,8 +4344,10 @@ namespace dxvk {
     if (!m_flags.test(DxvkContextFlag::GpRenderPassBound))
       this->startRenderPass();
     
-    if (m_flags.test(DxvkContextFlag::GpDirtyIndexBuffer) && Indexed)
-      this->updateIndexBufferBinding();
+    if (m_flags.test(DxvkContextFlag::GpDirtyIndexBuffer) && Indexed) {
+      if (unlikely(!this->updateIndexBufferBinding()))
+        return false;
+    }
     
     if (m_flags.test(DxvkContextFlag::GpDirtyVertexBuffers))
       this->updateVertexBufferBindings();

src/dxvk/dxvk_context.h

@@ -1162,7 +1162,7 @@ namespace dxvk {
 
     void updateFramebuffer();
     
-    void updateIndexBufferBinding();
+    bool updateIndexBufferBinding();
     void updateVertexBufferBindings();
 
     void updateTransformFeedbackBuffers();