Impostors: continue work on depth, getting closer

1 files changed, 17 insertions, 9 deletions

diff --git a/impostor.cginc b/impostor.cginc
index 184a8fe..e84f9db 100644
--- a/impostor.cginc
+++ b/impostor.cginc
@@ -67,9 +67,9 @@ float2 VirtualPlaneUV(float3 frameDir, float3 pivotToCam, float3 vertexToCam) {
 
 #if defined(_IMPOSTORS)
 
-// Decode linear 0-1 depth (0=near clip, 1=far clip) to world space distance from camera
+// Decode linear 0-1 depth (0=near clip, 1=far clip) to world space distance from camera.
 float DecodeImpostorDepth(float linearDepth) {
-    return _Impostors_Near_Clip + linearDepth * 2.0f * _Impostors_Sphere_Radius;
+    return lerp(_Impostors_Near_Clip, _Impostors_Far_Clip, linearDepth);
 }
 
 float2 ClampUvInCell(float2 uv) {
@@ -90,6 +90,8 @@ struct ImpostorResult {
     float metallic;
     float smoothness;
     float3 objPos;
+    // TODO rm
+    float debug;
 };
 
 float SampleImpostorDepthCell(float2 cell, float2 uvInCell, float gridRes) {
@@ -133,9 +135,13 @@ float2 ImpostorParallaxOffsetForFrame(float3 frameDir, float3 pivotToCamOS, floa
     float camZ = dot(pivotToCamOS, planeN);
     camZ = (abs(camZ) < 1e-4) ? (camZ < 0 ? -1e-4 : 1e-4) : camZ;
 
-    // Decode depth to world space, then normalize to [0,1] range
+    // Convert world-space depth to object space to match scaled impostor.
+    float objScale = max(2.0 * _Impostors_Sphere_Radius, 1e-4);
+    float objRadius = _Impostors_Sphere_Radius / objScale;
+    float objNear = _Impostors_Near_Clip / objScale;
     float worldSpaceDepth = DecodeImpostorDepth(encodedDepth);
-    float depth01 = (worldSpaceDepth - _Impostors_Near_Clip) / (2.0 * _Impostors_Sphere_Radius);
+    float objectSpaceDepth = worldSpaceDepth / objScale;
+    float depth01 = (objectSpaceDepth - objNear) / (2.0 * objRadius);
     // Convert to signed "height" where nearer pixels shift more (matches typical bump-offset convention).
     float zSurface = (depth01 - 0.5);
     float2 planeCoord = 0.5 - uvBase;
@@ -150,12 +156,14 @@ float3 ReconstructObjectOffsetFromFrame(float3 frameDir, float2 uv, float encode
     float3 planeX, planeY, planeN;
     FrameBasis(frameDir, planeX, planeY, planeN);
 
-    // UV offset from center, scaled to world units (baking camera spans [-Radius, Radius])
-    float2 offsetXY = (0.5 - uv) * 2.0 * _Impostors_Sphere_Radius;
+    float objScale = max(2.0f * _Impostors_Sphere_Radius, 1e-4);
+    float objRadius = _Impostors_Sphere_Radius / objScale;
+    float objNear = _Impostors_Near_Clip / objScale;
+    float objFar = _Impostors_Far_Clip / objScale;
 
-    // Decode depth to world space, convert to offset from center along view direction
-    float worldSpaceDepth = DecodeImpostorDepth(encodedDepth);
-    float offsetZ = (_Impostors_Sphere_Radius + _Impostors_Near_Clip) - worldSpaceDepth;
+    float2 offsetXY = (0.5f - uv) * 2.0f * objRadius;
+    float objectSpaceDepth = lerp(objNear, objFar, encodedDepth);
+    float offsetZ = (objRadius + objNear) - objectSpaceDepth;
 
     return offsetXY.x * planeX + offsetXY.y * planeY + offsetZ * planeN;
 }