[HDRP][Compositor] Fix outlines in transitions between post-processed and plain regions

com.unity.render-pipelines.high-definition/CHANGELOG.md

@@ -128,6 +128,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fixed error Maximum allowed thread group count is 65535 when resolution is very high. 
 - LOD meshes are now properly stripped based on the maximum lod value parameters contained in the HDRP asset.
 - Fixed an inconsistency in the LOD group UI where LOD bias was not the right one.
+- Fixed outlines in transitions between post-processed and plain regions in the graphics compositor (case 1278775).
 
 ### Changed
 - Preparation pass for RTSSShadows to be supported by render graph.

com.unity.render-pipelines.high-definition/Editor/Compositor/CompositionLayerUI.Drawers.cs

@@ -30,6 +30,7 @@ static partial class Styles
             static public readonly GUIContent k_AAMode = EditorGUIUtility.TrTextContent("Post Anti-aliasing", "To override the postprocess Anti-aliasing mode, activate the option by clicking on the check-box and then select the desired value.");
             static public readonly GUIContent k_CullingMask = EditorGUIUtility.TrTextContent("Culling Mask", "To override the culling mask, activate the option by clicking on the check-box and then select the desired value.");
             static public readonly GUIContent k_VolumeMask = EditorGUIUtility.TrTextContent("Volume Mask", "To override the volume mask, activate the option by clicking on the check-box and then select the desired value.");
+            static public readonly GUIContent k_AlphaRange = EditorGUIUtility.TrTextContent("Alpha Range", "The range of alpha values used when transitioning from post-processed to plain image regions. A smaller range will result in a steeper transition.");
 
             static public readonly string k_AlphaInfoPost = "The use of AOVs properties in a player require to to enable the Runtime AOV API support in the HDRP quality settings.";
 
@@ -178,6 +179,58 @@ public static void DrawStackedLayerProperties(Rect rect, SerializedCompositionLa
             rect.y += CompositorStyle.k_Spacing;
 
             EditorGUI.PropertyField(rect, serializedProperties.clearAlpha, Styles.k_ClearAlpha);
+            rect.y += 1.0f * CompositorStyle.k_Spacing;
+
+            // Draw a min/max slider for tha alpha range 
+            {
+                const float spacing = 5;
+                var labelRect = new Rect(rect.x, rect.y, EditorGUIUtility.labelWidth, rect.height);
+                EditorGUI.PrefixLabel(labelRect, Styles.k_AlphaRange);
+
+                var minLabelRect = rect;
+                minLabelRect.x += EditorGUIUtility.labelWidth;
+                minLabelRect.width = EditorGUIUtility.fieldWidth / 2;
+                serializedProperties.alphaMin.floatValue = EditorGUI.FloatField(minLabelRect, serializedProperties.alphaMin.floatValue);
+
+                GUI.SetNextControlName("AlphaMinMaxSlider");
+                var sliderRect = rect;
+                sliderRect.x += EditorGUIUtility.labelWidth + EditorGUIUtility.fieldWidth / 2 + spacing;
+                sliderRect.width -= (EditorGUIUtility.labelWidth + EditorGUIUtility.fieldWidth + 2 * spacing);
+                float minVal = serializedProperties.alphaMin.floatValue;
+                float maxVal = serializedProperties.alphaMax.floatValue;
+
+                EditorGUI.MinMaxSlider(sliderRect, ref minVal, ref maxVal, 0, 1);
+                if (serializedProperties.alphaMin.floatValue != minVal || serializedProperties.alphaMax.floatValue != maxVal)
+                {
+                    // Note: We need to move the focus when the slider changes, otherwise the textField will not update
+                    GUI.FocusControl("AlphaMinMaxSlider");
+                    serializedProperties.alphaMin.floatValue = minVal;
+                    serializedProperties.alphaMax.floatValue = maxVal;
+                }
+
+                var maxLabelRect = rect;
+                maxLabelRect.x = sliderRect.x + sliderRect.width + spacing;
+                maxLabelRect.width = EditorGUIUtility.fieldWidth / 2;
+                serializedProperties.alphaMax.floatValue = EditorGUI.FloatField(maxLabelRect, serializedProperties.alphaMax.floatValue);
+
+                // sanity checks
+                if (serializedProperties.alphaMax.floatValue < serializedProperties.alphaMin.floatValue)
+                {
+                    serializedProperties.alphaMax.floatValue = serializedProperties.alphaMin.floatValue;
+                }
+                if (serializedProperties.alphaMax.floatValue > 1)
+                {
+                    serializedProperties.alphaMax.floatValue = 1;
+                }
+                if (serializedProperties.alphaMin.floatValue > serializedProperties.alphaMax.floatValue)
+                {
+                    serializedProperties.alphaMin.floatValue = serializedProperties.alphaMax.floatValue;
+                }
+                if (serializedProperties.alphaMin.floatValue < 0)
+                {
+                    serializedProperties.alphaMin.floatValue = 0;
+                }
+            }
             rect.y += 1.5f * CompositorStyle.k_Spacing;
 
             // The clear mode should be visible / configurable only for the first layer in the stack. For the other layers we set a camera-stacking specific clear-mode .

com.unity.render-pipelines.high-definition/Editor/Compositor/SerializedCompositionLayer.cs

@@ -30,6 +30,8 @@ internal class SerializedCompositionLayer
         public SerializedProperty aovBitmask;
         public SerializedProperty inputFilters;
         public SerializedProperty positionInStack;
+        public SerializedProperty alphaMin;
+        public SerializedProperty alphaMax;
 
         public List<SerializedCompositionFilter> filterList = new List<SerializedCompositionFilter>();
 
@@ -60,6 +62,8 @@ public SerializedCompositionLayer(SerializedProperty root)
             aovBitmask = root.FindPropertyRelative("m_AOVBitmask");
             inputFilters = root.FindPropertyRelative("m_InputFilters");
             positionInStack = root.FindPropertyRelative("m_LayerPositionInStack");
+            alphaMin = root.FindPropertyRelative("m_AlphaMin");
+            alphaMax = root.FindPropertyRelative("m_AlphaMax");
 
             for (int index = 0; index < inputFilters.arraySize; index++)
             {
@@ -91,7 +95,8 @@ public float GetPropertiesHeight()
                     EditorGUI.GetPropertyHeight(cullingMaskProperty, null) +
                     EditorGUI.GetPropertyHeight(volumeMask, null) +
                     EditorGUI.GetPropertyHeight(inputFilters, null) +
-                    EditorGUIUtility.singleLineHeight * 7; //for the heading and pading
+                    EditorGUI.GetPropertyHeight(alphaMin, null) +   // we use a min/max slider in the UI so it takes a sinle line, so we don't need to count the alphaMax
+                    EditorGUIUtility.singleLineHeight * 7;          // for the heading and pading
 
                 if (inputFilters.arraySize > 0)
                 {

com.unity.render-pipelines.high-definition/Runtime/Compositor/AdditionalCompositorData.cs

@@ -17,6 +17,8 @@ internal class AdditionalCompositorData : MonoBehaviour
         public bool clearAlpha = true;    // Clearing the alpha allows the post process to run only on the pixels covered by a stacked camera (and not the previous ones).
         public BackgroundFitMode imageFitMode = BackgroundFitMode.Stretch;
         public List<CompositionFilter> layerFilters;
+        public float alphaMax = 1.0f;
+        public float alphaMin = 0.0f;
 
         public void Init(List<CompositionFilter> layerFilters, bool clearAlpha)
         {
@@ -36,6 +38,8 @@ public void ResetData()
                 layerFilters = null;
             }
 
+            alphaMax = 1.0f;
+            alphaMin = 0.0f;
         }
     }
 }

com.unity.render-pipelines.high-definition/Runtime/Compositor/CompositionLayer.cs

@@ -136,6 +136,10 @@ public float aspectRatio
         // Returns true if this layer is using a camera that was cloned internally for drawing
         bool isUsingACameraClone => !m_LayerCamera.Equals(m_Camera);
 
+        // The input alpha will be mapped between the min and max range when blending between the post-processed and plain image regions. This way the user can controls how steep is the transition.
+        [SerializeField] float m_AlphaMin = 0.0f;   
+        [SerializeField] float m_AlphaMax = 1.0f;
+
         private CompositorLayer()
         {
         }
@@ -469,6 +473,9 @@ public void SetAdditionalLayerData()
                 if (layerData != null)
                 {
                     layerData.Init(m_InputFilters, m_ClearAlpha);
+
+                    layerData.alphaMin = m_AlphaMin;
+                    layerData.alphaMax = m_AlphaMax;
                 }
             }
         }
@@ -507,7 +514,7 @@ public void UpdateOutputCamera()
             if (m_Type == LayerType.Image)
             {
                 var compositorData = m_LayerCamera.GetComponent<AdditionalCompositorData>();
-                if(compositorData)
+                if (compositorData)
                     compositorData.clearColorTexture = (m_Show && m_InputTexture != null) ? m_InputTexture : Texture2D.blackTexture;
             }
 

com.unity.render-pipelines.high-definition/Runtime/Compositor/CompositionManager.cs

@@ -838,5 +838,28 @@ static public Camera GetSceceCamera()
         static public CompositionManager GetInstance() =>
             s_CompositorInstance ?? (s_CompositorInstance = GameObject.FindObjectOfType(typeof(CompositionManager), true) as CompositionManager);
 
+        static public Vector4 GetAlphaScaleAndBiasForCamera(HDCamera hdCamera)
+        {
+            AdditionalCompositorData compositorData = null;
+            hdCamera.camera.TryGetComponent<AdditionalCompositorData>(out compositorData);
+
+            if (compositorData)
+            {
+                float alphaMin = compositorData.alphaMin;
+                float alphaMax = compositorData.alphaMax;
+
+                if (alphaMax == alphaMin)
+                    alphaMax += 0.0001f; // Mathf.Epsilon is too small and in this case it creates precission issues 
+
+                float alphaScale = 1.0f / (alphaMax - alphaMin);
+                float alphaBias = -alphaMin * alphaScale;
+
+                return new Vector4(alphaScale, alphaBias, 0.0f, 0.0f);
+            }
+
+            // No compositor-specific data for this camera/layer, just return the default/neutral scale and bias
+            return new Vector4(1.0f, 0.0f, 0.0f, 0.0f);
+        }
+
     }
 }

com.unity.render-pipelines.high-definition/Runtime/PostProcessing/PostProcessSystem.cs

@@ -885,6 +885,8 @@ struct UberPostParameters
             public Vector4          bloomBicubicParams;
             public Vector4          bloomDirtTileOffset;
             public Vector4          bloomThreshold;
+
+            public Vector4          alphaScaleBias;
         }
 
         UberPostParameters PrepareUberPostParameters(HDCamera hdCamera, bool isSceneView)
@@ -918,10 +920,23 @@ UberPostParameters PrepareUberPostParameters(HDCamera hdCamera, bool isSceneView
             PrepareChromaticAberrationParameters(ref parameters, featureFlags);
             PrepareVignetteParameters(ref parameters, featureFlags);
             PrepareUberBloomParameters(ref parameters, hdCamera);
+            PrepareAlphaScaleParameters(ref parameters, hdCamera);
 
             return parameters;
         }
 
+        void PrepareAlphaScaleParameters(ref UberPostParameters parameters, HDCamera camera)
+        {
+            if (m_EnableAlpha)
+            {
+                parameters.alphaScaleBias = Compositor.CompositionManager.GetAlphaScaleAndBiasForCamera(camera);
+            }
+            else
+            {
+                parameters.alphaScaleBias = new Vector4(1.0f, 0.0f, 0.0f, 0.0f);
+            }
+        }
+
         static void DoUberPostProcess(in UberPostParameters parameters,
                                         RTHandle source,
                                         RTHandle destination,
@@ -956,6 +971,8 @@ static void DoUberPostProcess(in UberPostParameters parameters,
             cmd.SetComputeVectorParam(parameters.uberPostCS, HDShaderIDs._BloomDirtScaleOffset, parameters.bloomDirtTileOffset);
             cmd.SetComputeVectorParam(parameters.uberPostCS, HDShaderIDs._BloomThreshold, parameters.bloomThreshold);
 
+            // Alpha scale and bias (only used when alpha is enabled)
+            cmd.SetComputeVectorParam(parameters.uberPostCS, HDShaderIDs._AlphaScaleBias, parameters.alphaScaleBias);
 
             // Dispatch uber post
             cmd.SetComputeVectorParam(parameters.uberPostCS, "_DebugFlags", new Vector4(parameters.outputColorLog ? 1 : 0, 0, 0, 0));

com.unity.render-pipelines.high-definition/Runtime/PostProcessing/Shaders/UberPost.compute

@@ -44,6 +44,7 @@ CBUFFER_START(cb0)
     float4 _BloomDirtScaleOffset;
     float4 _BloomBicubicParams;
     float4 _DebugFlags;
+    float4 _AlphaScaleBias;
 CBUFFER_END
 
 #define DistCenter              _DistortionParams1.xy
@@ -77,6 +78,9 @@ CBUFFER_END
 
 #define OutputLogEnabled        _DebugFlags.x
 
+#define AlphaScale              _AlphaScaleBias.x
+#define AlphaBias               _AlphaScaleBias.y
+
 float2 DistortUV(float2 uv)
 {
     // Lens distortion
@@ -218,8 +222,10 @@ void Uber(uint3 dispatchThreadId : SV_DispatchThreadID)
     // Alpha mask
 #ifdef ENABLE_ALPHA
         // Post processing is not applied on pixels with zero alpha
+        // The alpha scale and bias control how steep is the transition between the post-processed and plain regions
+        float alpha = inputColor.a * AlphaScale + AlphaBias;
         // Saturate is necessary to avoid issues when additive blending pushes the alpha over 1.
-        color.xyz = lerp(inputColor.xyz, color.xyz, saturate(inputColor.a));
+        color.xyz = lerp(inputColor.xyz, color.xyz, saturate(alpha));
 #endif
 
     // Done

com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/HDStringConstants.cs

@@ -714,6 +714,8 @@ static class HDShaderIDs
         public static readonly int _ChromaSpectralLut              = Shader.PropertyToID("_ChromaSpectralLut");
         public static readonly int _ChromaParams                   = Shader.PropertyToID("_ChromaParams");
 
+        public static readonly int _AlphaScaleBias                 = Shader.PropertyToID("_AlphaScaleBias");
+
         public static readonly int _VignetteParams1                = Shader.PropertyToID("_VignetteParams1");
         public static readonly int _VignetteParams2                = Shader.PropertyToID("_VignetteParams2");
         public static readonly int _VignetteColor                  = Shader.PropertyToID("_VignetteColor");