Workaround clear issue on Intel Skylake D3D driver

src/libANGLE/renderer/d3d/WorkaroundsD3D.h

@@ -94,6 +94,11 @@ struct WorkaroundsD3D
     // this bug, we use an expression to emulate function isnan(). Tracking bug:
     // https://crbug.com/650547
     bool emulateIsnanFloat = false;
+
+    // On some Intel drivers, using clear() may not take effect. One of such situation is to clear
+    // a target with width or height < 16. To work around this bug, we call clear() twice on these
+    // platforms. Tracking bug: https://crbug.com/655534
+    bool callClearTwiceOnSmallTarget = false;
 };
 
 }  // namespace rx

src/libANGLE/renderer/d3d/d3d11/Clear11.cpp

@@ -371,10 +371,24 @@ gl::Error Clear11::clearFramebuffer(const ClearParameters &clearParams,
                     rect.bottom = clearParams.scissor.y + clearParams.scissor.height;
 
                     deviceContext1->ClearView(framebufferRTV, clearValues, &rect, 1);
+                    if (mRenderer->getWorkarounds().callClearTwiceOnSmallTarget)
+                    {
+                        if (clearParams.scissor.width <= 16 || clearParams.scissor.height <= 16)
+                        {
+                            deviceContext1->ClearView(framebufferRTV, clearValues, &rect, 1);
+                        }
+                    }
                 }
                 else
                 {
                     deviceContext->ClearRenderTargetView(framebufferRTV, clearValues);
+                    if (mRenderer->getWorkarounds().callClearTwiceOnSmallTarget)
+                    {
+                        if (framebufferSize.width <= 16 || framebufferSize.height <= 16)
+                        {
+                            deviceContext->ClearRenderTargetView(framebufferRTV, clearValues);
+                        }
+                    }
                 }
             }
         }

src/libANGLE/renderer/d3d/d3d11/renderer11_utils.cpp

@@ -1859,6 +1859,8 @@ WorkaroundsD3D GenerateWorkarounds(const Renderer11DeviceCaps &deviceCaps,
         (IsBroadwell(adapterDesc.DeviceId) || IsHaswell(adapterDesc.DeviceId));
     workarounds.emulateIsnanFloat =
         IsIntel(adapterDesc.VendorId) && IsSkylake(adapterDesc.DeviceId);
+    workarounds.callClearTwiceOnSmallTarget =
+        IsIntel(adapterDesc.VendorId) && IsSkylake(adapterDesc.DeviceId);
 
     // TODO(jmadill): Disable when we have a fixed driver version.
     workarounds.emulateTinyStencilTextures = IsAMD(adapterDesc.VendorId);