Add workaround for flushing before readPixels.

src/libANGLE/renderer/Workarounds.h

@@ -44,7 +44,8 @@ struct Workarounds
         : mrtPerfWorkaround(false),
           setDataFasterThanImageUpload(false),
           zeroMaxLodWorkaround(false),
-          useInstancedPointSpriteEmulation(false)
+          useInstancedPointSpriteEmulation(false),
+          finishBeforeReadPixels(false)
     {}
 
     // On some systems, having extra rendertargets than necessary slows down the shader.
@@ -67,6 +68,12 @@ struct Workarounds
     // To work around this, D3D11 FL9_3 has to use a different pointsprite
     // emulation that is implemented using instanced quads.
     bool useInstancedPointSpriteEmulation;
+
+    // On some GPUs, race conditions have been observed during ReadPixels where GPU rendering is
+    // completing at the same time that the pixels are being mapped. This workaround governs whether
+    // a renderer finish is performed just before the readback operation. For performance reasons,
+    // it must not be done when using a pixel pack buffer.
+    bool finishBeforeReadPixels;
 };
 
 }

src/libANGLE/renderer/d3d/FramebufferD3D.cpp

@@ -258,6 +258,15 @@ gl::Error FramebufferD3D::readPixels(const gl::State &state, const gl::Rectangle
         return gl::Error(GL_INVALID_OPERATION, "invalid pixel store parameters in readPixels");
     }
 
+    if (!packState.pixelBuffer.get() && mRenderer->getWorkarounds().finishBeforeReadPixels)
+    {
+        gl::Error error = mRenderer->finish();
+        if (error.isError())
+        {
+            return error;
+        }
+    }
+
     GLenum sizedInternalFormat = gl::GetSizedInternalFormat(format, type);
     const gl::InternalFormat &sizedFormatInfo = gl::GetInternalFormatInfo(sizedInternalFormat);
     GLuint outputPitch = sizedFormatInfo.computeRowPitch(type, area.width, packState.alignment, 0);

src/libANGLE/renderer/d3d/d3d11/Renderer11.cpp

@@ -3667,7 +3667,7 @@ void Renderer11::generateCaps(gl::Caps *outCaps, gl::TextureCapsMap *outTextureC
 
 Workarounds Renderer11::generateWorkarounds() const
 {
-    return d3d11::GenerateWorkarounds(mRenderer11DeviceCaps.featureLevel);
+    return d3d11::GenerateWorkarounds(this);
 }
 
 void Renderer11::setShaderResource(gl::SamplerType shaderType, UINT resourceSlot, ID3D11ShaderResourceView *srv)

src/libANGLE/renderer/d3d/d3d11/Renderer11.h

@@ -260,7 +260,7 @@ class Renderer11 : public RendererD3D
                                    bool colorBlit, bool depthBlit, bool stencilBlit);
 
     bool isES3Capable() const;
-    const Renderer11DeviceCaps &getRenderer11DeviceCaps() { return mRenderer11DeviceCaps; };
+    const Renderer11DeviceCaps &getRenderer11DeviceCaps() const { return mRenderer11DeviceCaps; }
 
     RendererClass getRendererClass() const override { return RENDERER_D3D11; }
 

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

@@ -1236,13 +1236,15 @@ HRESULT SetDebugName(ID3D11DeviceChild *resource, const char *name)
 #endif
 }
 
-Workarounds GenerateWorkarounds(D3D_FEATURE_LEVEL featureLevel)
+Workarounds GenerateWorkarounds(const Renderer11 *renderer)
 {
+    D3D_FEATURE_LEVEL featureLevel = renderer->getRenderer11DeviceCaps().featureLevel;
     Workarounds workarounds;
     workarounds.mrtPerfWorkaround = true;
     workarounds.setDataFasterThanImageUpload = true;
     workarounds.zeroMaxLodWorkaround = (featureLevel <= D3D_FEATURE_LEVEL_9_3);
     workarounds.useInstancedPointSpriteEmulation = (featureLevel <= D3D_FEATURE_LEVEL_9_3);
+    workarounds.finishBeforeReadPixels = renderer->getVendorId() == VENDOR_ID_AMD;
     return workarounds;
 }
 

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

@@ -24,6 +24,7 @@ class FramebufferAttachment;
 
 namespace rx
 {
+class Renderer11;
 class RenderTarget11;
 struct Workarounds;
 struct Renderer11DeviceCaps;
@@ -278,7 +279,7 @@ void SetBufferData(ID3D11DeviceContext *context, ID3D11Buffer *constantBuffer, c
     }
 }
 
-Workarounds GenerateWorkarounds(D3D_FEATURE_LEVEL featureLevel);
+Workarounds GenerateWorkarounds(const Renderer11 *renderer);
 
 }
 

src/libANGLE/renderer/d3d/d3d9/renderer9_utils.cpp

@@ -581,6 +581,9 @@ Workarounds GenerateWorkarounds()
     workarounds.mrtPerfWorkaround = true;
     workarounds.setDataFasterThanImageUpload = false;
     workarounds.useInstancedPointSpriteEmulation = false;
+    // Flakiness has been observed in WebGL conformance tests using
+    // ReadPixels on all vendors' GPUs with the D3D9 backend.
+    workarounds.finishBeforeReadPixels = true;
     return workarounds;
 }