RenderWidget: Hook up to ImGui

Source/Core/VideoCommon/RenderBase.cpp

@@ -812,9 +812,18 @@ void Renderer::DrawImGui()
   }
 }
 
+std::unique_lock<std::mutex> Renderer::GetImGuiLock()
+{
+  return std::unique_lock<std::mutex>(m_imgui_mutex);
+}
+
 void Renderer::Swap(u32 xfbAddr, u32 fbWidth, u32 fbStride, u32 fbHeight, const EFBRectangle& rc,
                     u64 ticks)
 {
+  // Hold the imgui lock while we're presenting.
+  // It's only to prevent races on inputs anyway, at this point.
+  std::unique_lock<std::mutex> imgui_lock(m_imgui_mutex);
+
   const AspectMode suggested = g_ActiveConfig.suggested_aspect_mode;
   if (suggested == AspectMode::Analog || suggested == AspectMode::AnalogWide)
   {

Source/Core/VideoCommon/RenderBase.h

@@ -188,6 +188,11 @@ public:
 
   virtual std::unique_ptr<VideoCommon::AsyncShaderCompiler> CreateAsyncShaderCompiler();
 
+  // Returns a lock for the ImGui mutex, enabling data structures to be modified from outside.
+  // Use with care, only non-drawing functions should be called from outside the video thread,
+  // as the drawing is tied to a "frame".
+  std::unique_lock<std::mutex> GetImGuiLock();
+
 protected:
   std::tuple<int, int> CalculateTargetScale(int x, int y) const;
   bool CalculateTargetSize();
@@ -243,6 +248,7 @@ protected:
   std::unique_ptr<NativeVertexFormat> m_imgui_vertex_format;
   std::vector<std::unique_ptr<AbstractTexture>> m_imgui_textures;
   std::unique_ptr<AbstractPipeline> m_imgui_pipeline;
+  std::mutex m_imgui_mutex;
   u64 m_imgui_last_frame_time;
 
 private: