Fix issue 1354395 where the right eye was shifted in stereo mode (#5789)

This commit Unity-Technologies/PostProcessing@08b1319 forced a reset on the projection matrix in PreCull and PostRender to avoid issues when switching on/off the TAA.
This is fine except that it doesn't reset the projection matrix to the device's projection matrix which seems to trickle down somewhere and result in some systems getting the wrong projection matrix.

This fix consist in forcing the device's projection matrix onto the camera to make sure that everyone is using the correct matrix if we happen to be in stereo.
PostRender doesn't need to copy from device because the Render step of the TAA PostProcessLayer performs that action.
PostRender doesn't need to deal with unjittered because that's probably only used in TAA.

Author: fcoulombe

com.unity.postprocessing/PostProcessing/Runtime/PostProcessLayer.cs

@@ -447,14 +447,35 @@ void OnPreCull()
 #if UNITY_2018_2_OR_NEWER
                 if (!m_Camera.usePhysicalProperties)
 #endif
-                m_Camera.ResetProjectionMatrix();
+                {
+                    m_Camera.ResetProjectionMatrix();
+                    m_Camera.nonJitteredProjectionMatrix = m_Camera.projectionMatrix;
+#if (ENABLE_VR_MODULE && ENABLE_VR)
+                    if (m_Camera.stereoEnabled)
+                    {
+                        m_Camera.ResetStereoProjectionMatrices();
+                        if (m_Camera.stereoActiveEye == Camera.MonoOrStereoscopicEye.Right)
+                        {
+                            m_Camera.CopyStereoDeviceProjectionMatrixToNonJittered(Camera.StereoscopicEye.Right);
+                            m_Camera.projectionMatrix = m_Camera.GetStereoNonJitteredProjectionMatrix(Camera.StereoscopicEye.Right);
+                            m_Camera.nonJitteredProjectionMatrix = m_Camera.projectionMatrix;
+                            m_Camera.SetStereoProjectionMatrix(Camera.StereoscopicEye.Right, m_Camera.GetStereoProjectionMatrix(Camera.StereoscopicEye.Right));
+                        }
+                        else if (m_Camera.stereoActiveEye == Camera.MonoOrStereoscopicEye.Left || m_Camera.stereoActiveEye == Camera.MonoOrStereoscopicEye.Mono)
+                        {
+                            m_Camera.CopyStereoDeviceProjectionMatrixToNonJittered(Camera.StereoscopicEye.Left); // device to unjittered
+                            m_Camera.projectionMatrix = m_Camera.GetStereoNonJitteredProjectionMatrix(Camera.StereoscopicEye.Left);
+                            m_Camera.nonJitteredProjectionMatrix = m_Camera.projectionMatrix;
+                            m_Camera.SetStereoProjectionMatrix(Camera.StereoscopicEye.Left, m_Camera.GetStereoProjectionMatrix(Camera.StereoscopicEye.Left));
+                        }
+                    }
+#endif
+                }
             }
-            m_Camera.nonJitteredProjectionMatrix = m_Camera.projectionMatrix;
 
 #if (ENABLE_VR_MODULE && ENABLE_VR)
             if (m_Camera.stereoEnabled)
             {
-                m_Camera.ResetStereoProjectionMatrices();
                 Shader.SetGlobalFloat(ShaderIDs.RenderViewportScaleFactor, XRSettings.renderViewportScale);
             }
             else
@@ -689,12 +710,19 @@ void OnPostRender()
                     m_Camera.usePhysicalProperties = true;
                 else
 #endif
-                m_Camera.ResetProjectionMatrix();
-
-                if (m_CurrentContext.stereoActive)
                 {
-                    if (RuntimeUtilities.isSinglePassStereoEnabled || m_Camera.stereoActiveEye == Camera.MonoOrStereoscopicEye.Right)
-                        m_Camera.ResetStereoProjectionMatrices();
+                    // The camera must be reset on precull and post render to avoid issues with alpha when toggling TAA.
+                    m_Camera.ResetProjectionMatrix();
+                    if (m_CurrentContext.stereoActive)
+                    {
+                        if (RuntimeUtilities.isSinglePassStereoEnabled || m_Camera.stereoActiveEye == Camera.MonoOrStereoscopicEye.Right)
+                        {
+                            m_Camera.ResetStereoProjectionMatrices();
+                            // copy the left eye onto the projection matrix so that we're using the correct projection matrix after calling m_Camera.ResetProjectionMatrix(); above.
+                            if (XRSettings.stereoRenderingMode == XRSettings.StereoRenderingMode.MultiPass)
+                                m_Camera.projectionMatrix = m_Camera.GetStereoProjectionMatrix(Camera.StereoscopicEye.Left);
+                        }
+                    }
                 }
             }
         }