Add Cube Blitting

Yeouch signed cube blitting sucks!

Almost wish I stayed with the numerical derivatives...  hell, a numerical derivative here would probably be cheaper...

Assets/Volume/Resources/DistanceFieldTexture.shader

@@ -66,7 +66,7 @@
 					alpha += 0.2; //This is like the near clipping plane
 				}
 
-				for(int i=1; i<20; i++) {
+				for(int i=0; i<20; i++) {
 				  float3 pos = startingPos - (viewDirection*alpha);
 				  if(valid && (abs(pos.x)>0.501 || abs(pos.y)>0.501 || abs(pos.z)>0.501)){
 						valid = false;

Assets/Volume/Resources/blitCube.shader

@@ -0,0 +1,63 @@
+Shader "Unlit/blitCube"
+{
+    Properties
+    {
+        _Center ("Center", Vector) = (0.5,0.5,0.5,0.0)
+        _Extent ("Extent", Vector) = (0.15,0.15,0.15,0.0)
+    }
+
+    SubShader
+    {
+        Lighting Off
+        Blend One Zero
+
+        Pass
+        {
+            CGPROGRAM
+            #include "UnityCustomRenderTexture.cginc"
+
+            #pragma vertex CustomRenderTextureVertexShader
+            #pragma fragment frag
+
+            float3 _Center;
+            float3 _Extent;
+
+			//WHY IS NEAREST POINT ON THE SURFACE OF A CUBE SO HARD
+            float4 frag(v2f_customrendertexture IN) : COLOR
+            {
+				float4 col = tex3D(_SelfTexture3D, IN.globalTexcoord + float3(0, 0, 0.5/_CustomRenderTextureDepth));
+				float3 boxSpacePos = (IN.globalTexcoord - _Center.xyz);
+				float distMultiplier = 1.0;
+
+				if(abs(boxSpacePos.x) < _Extent.x && 
+				   abs(boxSpacePos.y) < _Extent.y && 
+				   abs(boxSpacePos.z) < _Extent.z){
+					float maxCoord = max(max(abs(boxSpacePos.x), 
+											 abs(boxSpacePos.y)), 
+											 abs(boxSpacePos.z));
+					if(maxCoord == abs(boxSpacePos.x)){
+						boxSpacePos.x = sign(boxSpacePos.x) * _Extent.x;
+					}else if(maxCoord == abs(boxSpacePos.y)){
+						boxSpacePos.y = sign(boxSpacePos.y) * _Extent.y;
+					}else if(maxCoord == abs(boxSpacePos.z)){
+						boxSpacePos.z = sign(boxSpacePos.z) * _Extent.z;
+					}
+					distMultiplier *= -1.0;
+				} else {
+					boxSpacePos = float3(sign(boxSpacePos.x) * min(abs(boxSpacePos.x), _Extent.x), 
+										 sign(boxSpacePos.y) * min(abs(boxSpacePos.y), _Extent.y), 
+										 sign(boxSpacePos.z) * min(abs(boxSpacePos.z), _Extent.z));
+				}
+
+				float3 posOnSurface = (boxSpacePos+_Center.xyz);
+				float newDistance = length(IN.globalTexcoord-posOnSurface) * distMultiplier;
+				if(newDistance<col.a){
+					col.rgb = (IN.globalTexcoord-posOnSurface)/newDistance;
+					col.a = newDistance;
+				}
+				return col;
+            }
+            ENDCG
+        }
+    }
+}