Ensure custom shader output is updated before fetching histogram

* The custom shader output is updated when displaying, but this can lag by a
  call or two (a 'frame' if you like) when the display is only triggered by a
  window repaint and the histogram can be fetched first. Since the custom shader
  apply is only expensive when we need to recreate the output texture, we can do
  it on-demand similar to what we do with the overlay texture.

renderdoc/replay/replay_controller.h

@@ -79,6 +79,7 @@ private:
 
   ReplayController *m_pController;
 
+  bool m_CustomDirty;
   bool m_OverlayDirty;
   bool m_ForceOverlayRefresh;
 

renderdoc/replay/replay_output.cpp

@@ -92,6 +92,7 @@ ReplayOutput::ReplayOutput(ReplayController *parent, WindowingData window, Repla
 
   m_MainOutput.dirty = true;
 
+  m_CustomDirty = false;
   m_OverlayDirty = false;
   m_ForceOverlayRefresh = false;
 
@@ -196,6 +197,7 @@ void ReplayOutput::SetTextureDisplay(const TextureDisplay &o)
   }
   if(wasClearBeforeDraw && o.backgroundColor != m_RenderData.texDisplay.backgroundColor)
     m_OverlayDirty = true;
+  m_CustomDirty = true;
   m_RenderData.texDisplay = o;
   m_MainOutput.dirty = true;
 }
@@ -217,6 +219,7 @@ void ReplayOutput::SetFrameEvent(int eventId)
   m_EventID = eventId;
 
   m_OverlayDirty = (m_RenderData.texDisplay.overlay != DebugOverlay::NoOverlay);
+  m_CustomDirty = true;
   m_MainOutput.dirty = true;
 
   for(size_t i = 0; i < m_Thumbnails.size(); i++)
@@ -298,6 +301,18 @@ ResourceId ReplayOutput::GetCustomShaderTexID()
 {
   CHECK_REPLAY_THREAD();
 
+  if(m_CustomDirty)
+  {
+    TextureDisplay texDisplay = m_RenderData.texDisplay;
+    texDisplay.rawOutput = false;
+    texDisplay.resourceId = m_pDevice->GetLiveID(texDisplay.resourceId);
+
+    m_CustomShaderResourceId = m_pDevice->ApplyCustomShader(texDisplay);
+    m_pController->FatalErrorCheck();
+
+    m_CustomDirty = false;
+  }
+
   return m_CustomShaderResourceId;
 }
 
@@ -768,6 +783,8 @@ void ReplayOutput::DisplayTex()
     texDisplay.typeCast = CompType::Typeless;
     texDisplay.customShaderId = ResourceId();
     texDisplay.subresource.slice = 0;
+
+    m_CustomDirty = false;
   }
 
   FloatVector color;