Impostors: continue work on depth

1 files changed, 27 insertions, 16 deletions

diff --git a/impostor.cginc b/impostor.cginc
index b49dfce..184a8fe 100644
--- a/impostor.cginc
+++ b/impostor.cginc
@@ -67,6 +67,11 @@ 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
+float DecodeImpostorDepth(float linearDepth) {
+    return _Impostors_Near_Clip + linearDepth * 2.0f * _Impostors_Sphere_Radius;
+}
+
 float2 ClampUvInCell(float2 uv) {
     uv = saturate(uv);
     float2 halfTexelInCell = 0.5 * _Impostors_Atlas_TexelSize.xy * (float)_Impostors_Grid_Resolution;
@@ -93,6 +98,7 @@ float SampleImpostorDepthCell(float2 cell, float2 uvInCell, float gridRes) {
     float2 atlasUv = (cell + uvInCell) * invGridRes;
     float2 gradX = ddx(uvInCell) * invGridRes;
     float2 gradY = ddy(uvInCell) * invGridRes;
+    // 0 = near clip plane, 1 = far clip plane
     return _Impostors_Depth_Atlas.SampleGrad(bilinear_clamp_s, atlasUv, gradX, gradY).r;
 }
 
@@ -119,7 +125,7 @@ ImpostorSample SampleImpostorCell(float2 cell, float2 uvInCell, float gridRes) {
     return s;
 }
 
-float2 ImpostorParallaxOffsetForFrame(float3 frameDir, float3 pivotToCamOS, float2 uvBase, float depth01) {
+float2 ImpostorParallaxOffsetForFrame(float3 frameDir, float3 pivotToCamOS, float2 uvBase, float encodedDepth) {
     float3 planeX, planeY, planeN;
     FrameBasis(frameDir, planeX, planeY, planeN);
 
@@ -127,7 +133,9 @@ float2 ImpostorParallaxOffsetForFrame(float3 frameDir, float3 pivotToCamOS, floa
     float camZ = dot(pivotToCamOS, planeN);
     camZ = (abs(camZ) < 1e-4) ? (camZ < 0 ? -1e-4 : 1e-4) : camZ;
 
-    // Bake depth is linear in ortho: 0=near surface, 1=far surface.
+    // Decode depth to world space, then normalize to [0,1] range
+    float worldSpaceDepth = DecodeImpostorDepth(encodedDepth);
+    float depth01 = (worldSpaceDepth - _Impostors_Near_Clip) / (2.0 * _Impostors_Sphere_Radius);
     // Convert to signed "height" where nearer pixels shift more (matches typical bump-offset convention).
     float zSurface = (depth01 - 0.5);
     float2 planeCoord = 0.5 - uvBase;
@@ -135,19 +143,19 @@ float2 ImpostorParallaxOffsetForFrame(float3 frameDir, float3 pivotToCamOS, floa
     return (planeCoord - camXY) * (zSurface / camZ);
 }
 
-// Reconstruct object space position from frame UV and depth.
-// UV encodes X,Y on the virtual plane (0.5 = center), depth encodes Z (0.5 = center).
-// The baked orthographic view spans [-Radius, Radius] in each axis.
-float3 ReconstructObjPosFromFrame(float3 frameDir, float2 uv, float depth) {
+// Reconstruct object-space offset from impostor center.
+// frameDir: object-space direction from center to baking camera (same space as UV computation)
+// UV encodes X,Y on the virtual plane (0.5 = center), depth is linear 0-1 (near to far clip).
+float3 ReconstructObjectOffsetFromFrame(float3 frameDir, float2 uv, float encodedDepth) {
     float3 planeX, planeY, planeN;
     FrameBasis(frameDir, planeX, planeY, planeN);
 
-    // Invert VirtualPlaneUV: offset = 0.5 - uv, scale by diameter
+    // UV offset from center, scaled to world units (baking camera spans [-Radius, Radius])
     float2 offsetXY = (0.5 - uv) * 2.0 * _Impostors_Sphere_Radius;
 
-    // Depth 0 = front (toward camera), 0.5 = center, 1 = back (away from camera)
-    // planeN points toward camera, so positive Z = toward camera
-    float offsetZ = (0.5 - depth) * 2.0 * _Impostors_Sphere_Radius;
+    // 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;
 
     return offsetXY.x * planeX + offsetXY.y * planeY + offsetZ * planeN;
 }
@@ -310,16 +318,19 @@ ImpostorResult impostor_frag(float3 worldPos) {
     result.metallic = blended.metallicGloss.r;
     result.smoothness = blended.metallicGloss.a;
 
-    // Reconstruct object space position from each frame's base UV and depth, then blend.
-    // Using base UVs and base depths ensures geometric consistency (same texel location).
+    // Reconstruct object-space position from each frame's UV and depth, then blend.
     float depth0Pos = SampleImpostorDepthCell(cell0, uv0Final, gridRes);
     float depth1Pos = SampleImpostorDepthCell(cell1, uv1Final, gridRes);
     float depth2Pos = SampleImpostorDepthCell(cell2, uv2Final, gridRes);
 
-    float3 objPos0 = ReconstructObjPosFromFrame(frameDir0, uv0Final, depth0Pos);
-    float3 objPos1 = ReconstructObjPosFromFrame(frameDir1, uv1Final, depth1Pos);
-    float3 objPos2 = ReconstructObjPosFromFrame(frameDir2, uv2Final, depth2Pos);
-    result.objPos = objPos0 * bw.x + objPos1 * bw.y + objPos2 * bw.z;
+    // Use object-space frame directions (same space as UV computation)
+    float3 offset0 = ReconstructObjectOffsetFromFrame(frameDir0, uv0Final, depth0Pos);
+    float3 offset1 = ReconstructObjectOffsetFromFrame(frameDir1, uv1Final, depth1Pos);
+    float3 offset2 = ReconstructObjectOffsetFromFrame(frameDir2, uv2Final, depth2Pos);
+    float3 objOffset = offset0 * bw.x + offset1 * bw.y + offset2 * bw.z;
+
+    // Return object-space position (offset from origin)
+    result.objPos = objOffset;
 
     return result;
 }