flip sign option

Editor/MeshToSDFEditor.cs

@@ -5,6 +5,7 @@ using UnityEditor;
 public class MeshToSDFEditor : Editor
 {
     SerializedProperty m_SDFTexture;
+    SerializedProperty m_FlipSign;
     SerializedProperty m_FloodMode;
     SerializedProperty m_FloodFillQuality;
     SerializedProperty m_FloodFillIterations;
@@ -14,6 +15,7 @@ public class MeshToSDFEditor : Editor
     void OnEnable()
     {
         m_SDFTexture = serializedObject.FindProperty("m_SDFTexture");
+        m_FlipSign = serializedObject.FindProperty("m_FlipSign");
         m_FloodMode = serializedObject.FindProperty("m_FloodMode");
         m_FloodFillQuality = serializedObject.FindProperty("m_FloodFillQuality");
         m_FloodFillIterations = serializedObject.FindProperty("m_FloodFillIterations");
@@ -50,12 +52,26 @@ public class MeshToSDFEditor : Editor
         else
         {
             GUI.enabled = false;
-            int oldValue = m_DistanceMode.enumValueIndex;
+
+            int oldDistanceMode = m_DistanceMode.enumValueIndex;
             m_DistanceMode.enumValueIndex = (int)MeshToSDF.DistanceMode.Unsigned;
             EditorGUILayout.PropertyField(m_DistanceMode);
-            m_DistanceMode.enumValueIndex = oldValue;
+            m_DistanceMode.enumValueIndex = oldDistanceMode;
+            
             GUI.enabled = true;
         }
+
+        if ((MeshToSDF.FloodMode)m_FloodMode.enumValueIndex == MeshToSDF.FloodMode.Linear && (MeshToSDF.DistanceMode)m_DistanceMode.enumValueIndex == MeshToSDF.DistanceMode.Signed)
+        {
+            EditorGUILayout.PropertyField(m_FlipSign);
+        }
+        else
+        {
+            bool oldFlipSign = m_FlipSign.boolValue;
+            m_FlipSign.boolValue = false;
+            EditorGUILayout.PropertyField(m_FlipSign);
+            m_FlipSign.boolValue = oldFlipSign;
+        }
         
         serializedObject.ApplyModifiedProperties();
     }

Runtime/MeshToSDF.cs

@@ -47,12 +47,17 @@ If you need signed distance or just need a limited shell around your surface, us
     [SerializeField]
     DistanceMode m_DistanceMode = DistanceMode.Signed;
     [SerializeField]
+    [Tooltip("Flip the sign of the distance field, so that the interior is positive and exterior - negative.")]
+    bool m_FlipSign = false;
+    [SerializeField]
     UpdateMode m_UpdateMode = UpdateMode.OnBeginFrame;
 
     public SDFTexture sdfTexture { get { return m_SDFTexture; } set { m_SDFTexture = value; } }
+    public bool flipSign { get { return m_FlipSign; } set { m_FlipSign = value; } }
     public FloodMode floodMode  { get { return m_FloodMode; } set { m_FloodMode = value; } }
     public FloodFillQuality floodFillQuality  { get { return m_FloodFillQuality; } set { m_FloodFillQuality = value; } }
     public int floodFillIterations  { get { return m_FloodFillIterations; } set { m_FloodFillIterations = Mathf.Clamp(value, 0, 64); } }
+    public DistanceMode distanceMode { get { return m_DistanceMode; } set { m_DistanceMode = value; } }
     public UpdateMode updateMode { get {return m_UpdateMode; } set { m_UpdateMode = value; } }
 
     [SerializeField]
@@ -104,6 +109,7 @@ If you need signed distance or just need a limited shell around your surface, us
         internal static int g_NumCellsZ = Shader.PropertyToID("g_NumCellsZ");
         internal static int g_Origin = Shader.PropertyToID("g_Origin");
         internal static int g_CellSize = Shader.PropertyToID("g_CellSize");
+        internal static int g_FlipSign = Shader.PropertyToID("g_FlipSign");
         internal static int g_VertexBuffer = Shader.PropertyToID("g_VertexBuffer");
         internal static int g_IndexBuffer = Shader.PropertyToID("g_IndexBuffer");
         internal static int _VertexBufferStride = Shader.PropertyToID("_VertexBufferStride");
@@ -240,6 +246,7 @@ If you need signed distance or just need a limited shell around your surface, us
         cmd.SetComputeIntParam(m_Compute, Uniforms.g_NumCellsX, voxelResolution.x);
         cmd.SetComputeIntParam(m_Compute, Uniforms.g_NumCellsY, voxelResolution.y);
         cmd.SetComputeIntParam(m_Compute, Uniforms.g_NumCellsZ, voxelResolution.z);
+        cmd.SetComputeFloatParam(m_Compute, Uniforms.g_FlipSign, m_FlipSign ? -1 : 1);
         int[] voxelResolutionArray = {voxelResolution.x, voxelResolution.y, voxelResolution.z, voxelCount};
         cmd.SetComputeIntParams(m_Compute, Uniforms._VoxelResolution, voxelResolutionArray);
         float maxDistance = voxelBounds.size.magnitude;

_External/TressFXSDF.hlsl

@@ -28,6 +28,7 @@ float g_CellSize;
 int g_NumCellsX;
 int g_NumCellsY;
 int g_NumCellsZ;
+float g_FlipSign;
 
 #define MARGIN g_CellSize
 #define GRID_MARGIN int3(1, 1, 1)
@@ -204,6 +205,7 @@ float SignedDistancePointToTriangle(float3 p, float3 x0, float3 x1, float3 x2)
 
 #ifdef SIGNED
 	d = (dot(p - x0, nTri) < 0.f) ? -d : d;
+	d *= g_FlipSign;
 #endif
 
 	return d;