GPU: Ensure batches are flushed before presenting frame

Fixes occasional assertion failing when using the debugger.

src/core/gpu_backend.h

@@ -90,6 +90,9 @@ public:
   // TODO: replace with "invalidate cached state"
   virtual void RestoreDeviceContext() = 0;
 
+  /// Ensures all pending draws are flushed to the host GPU.
+  virtual void FlushRender() = 0;
+
   /// Main command handler for GPU thread.
   void HandleCommand(const GPUThreadCommand* cmd);
 
@@ -140,9 +143,6 @@ protected:
   virtual bool AllocateMemorySaveState(System::MemorySaveState& mss, Error* error) = 0;
   virtual void DoMemoryState(StateWrapper& sw, System::MemorySaveState& mss) = 0;
 
-  /// Ensures all pending draws are flushed to the host GPU.
-  virtual void FlushRender() = 0;
-
   /// Helper function for computing the draw rectangle in a larger window.
   void CalculateDrawRect(s32 window_width, s32 window_height, bool apply_rotation, bool apply_aspect_ratio,
                          GSVector4i* display_rect, GSVector4i* draw_rect) const;

src/core/gpu_hw.h

@@ -71,6 +71,7 @@ public:
   u32 GetResolutionScale() const override;
 
   void RestoreDeviceContext() override;
+  void FlushRender() override;
 
 protected:
   void UpdateSettings(const GPUSettings& old_settings) override;
@@ -91,7 +92,6 @@ protected:
   void DrawLine(const GPUBackendDrawLineCommand* cmd) override;
   void DrawPreciseLine(const GPUBackendDrawPreciseLineCommand* cmd) override;
 
-  void FlushRender() override;
   void DrawingAreaChanged() override;
   void ClearVRAM() override;
 

src/core/gpu_sw.h

@@ -23,6 +23,7 @@ public:
   bool Initialize(bool upload_vram, Error* error) override;
 
   void RestoreDeviceContext() override;
+  void FlushRender() override;
 
   u32 GetResolutionScale() const override;
 
@@ -46,8 +47,6 @@ protected:
 
   void ClearVRAM() override;
 
-  void FlushRender() override;
-
   void UpdateResolutionScale() override;
 
   void LoadState(const GPUBackendLoadStateCommand* cmd) override;

src/core/gpu_thread.cpp

@@ -1215,6 +1215,9 @@ void GPUThread::SleepUntilPresentTime(Timer::Value present_time)
 
 void GPUThread::Internal::PresentFrame(bool allow_skip_present, u64 present_time)
 {
+  if (s_state.gpu_backend)
+    s_state.gpu_backend->FlushRender();
+
   const bool skip_present = (!g_gpu_device->HasMainSwapChain() ||
                              (allow_skip_present && g_gpu_device->GetMainSwapChain()->ShouldSkipPresentingFrame() &&
                               s_state.skipped_present_count < MAX_SKIPPED_PRESENT_COUNT));