Add quad overdraw mode. Thanks Stephen Hill (@self_shadow)!

* http://blog.selfshadow.com/2012/11/12/counting-quads/
* Quad Overdraw based on ScenePS4 from the revised implementation. The
  colours are new, up to 20 levels. Picking pixels shows the overdraw level
* Available per-pass and per-drawcall, a pass defined the same way as in
  the mesh view, drawcalls since last clear or RT change.
* List of events now passed through to RenderOverlay the same as RenderMesh

renderdocui/Interop/Enums.cs

@@ -125,6 +125,8 @@ namespace renderdoc
         ViewportScissor,
         NaN,
         Clipping,
+        QuadOverdrawPass,
+        QuadOverdrawDraw,
     };
 
     public enum SpecialFormat

renderdocui/Windows/TextureViewer.Designer.cs

@@ -554,7 +554,9 @@
             "Stencil Test",
             "Viewport/Scissor Region",
             "NaN/INF/-ve Display",
-            "Clipping"});
+            "Clipping",
+            "Quad Overdraw (Pass)",
+            "Quad Overdraw (Draw)"});
             this.overlay.Name = "overlay";
             this.overlay.Size = new System.Drawing.Size(121, 25);
             this.overlay.SelectedIndexChanged += new System.EventHandler(this.overlay_SelectedIndexChanged);

renderdocui/Windows/TextureViewer.cs

@@ -1331,6 +1331,14 @@ namespace renderdocui.Windows
             bool uintTex = (tex.format.compType == FormatComponentType.UInt);
             bool sintTex = (tex.format.compType == FormatComponentType.SInt);
 
+            if (m_TexDisplay.overlay == TextureDisplayOverlay.QuadOverdrawPass ||
+                m_TexDisplay.overlay == TextureDisplayOverlay.QuadOverdrawDraw)
+            {
+                dsv = false;
+                uintTex = false;
+                sintTex = true;
+            }
+
             if (m_CurHoverValue != null)
             {
                 if (dsv || uintTex || sintTex)