Impostors: fix bounding sphere scale

4 files changed, 84 insertions, 31 deletions

diff --git a/3ner.cginc b/3ner.cginc
index a6900d3..1788116 100644
--- a/3ner.cginc
+++ b/3ner.cginc
@@ -30,9 +30,7 @@ v2f vert(appdata v) {
   UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(o);
 
 #if defined(_IMPOSTORS)
-  float3 impostorWorldPos = mul(unity_ObjectToWorld, v.vertex);
-  impostor_vert(v.vertex, impostorWorldPos);
-  v.vertex = mul(unity_WorldToObject, float4(impostorWorldPos, 1));
+  impostor_vert(v.vertex.xyz);
 #endif
 
 #if defined(_TESSELLATION)
@@ -253,10 +251,19 @@ void geom(triangle v2f tri_in[3],
 }
 //endex
 
-float4 frag(v2f i, uint facing : SV_IsFrontFace) : SV_Target {
+struct FragOut {
+  float4 color;
+#if defined(_IMPOSTORS)
+  float depth : SV_DepthLessEqual;
+#endif
+};
+
+FragOut frag(v2f i, uint facing : SV_IsFrontFace) : SV_Target {
+  FragOut result = (FragOut) 0;
+
   UNITY_SETUP_INSTANCE_ID(i);
 #if defined(SHADOW_CASTER_PASS)
-  return 0;
+  return result;
 #endif
 
 #if defined(_RAY_MARCHING)
@@ -276,14 +283,20 @@ float4 frag(v2f i, uint facing : SV_IsFrontFace) : SV_Target {
 
 #if defined(_IMPOSTORS)
   i.normal = pbr.normal;
+  i.objPos = pbr.objPos;
+  propagateObjPos(i);
+  result.depth = i.pos.z;
 #endif
 
 #if defined(_DEBUG_VIEW_UNLIT)
-  return pbr.albedo;
+  result.color = pbr.albedo;
+  return result;
 #elif defined(_DEBUG_VIEW_WORLD_SPACE_NORMALS)
-  return float4((pbr.normal + 1.0f) * 0.5f, 1);
+  result.color = float4((pbr.normal + 1.0f) * 0.5f, 1);
+  return result;
 #elif defined(_DEBUG_VIEW_METALLIC_GLOSS)
-  return float4(pbr.metallic, pbr.smoothness, 0, 1);
+  result.color = float4(pbr.metallic, pbr.smoothness, 0, 1);
+  return result;
 #endif
 
   LightData light_data;
@@ -291,9 +304,11 @@ float4 frag(v2f i, uint facing : SV_IsFrontFace) : SV_Target {
 
 #if 0
   float c = light_data.common.NoV;
-  return float4(c,c,c,1);
+  result.color = float4(c,c,c,1);
+  return result;
 #endif
-  return brdf(pbr, light_data);
+  result.color = brdf(pbr, light_data);
+  return result;
 }
 
 #endif  // __3NER_INC
diff --git a/Scripts/Impostors.cs b/Scripts/Impostors.cs
index a2c205c..e52452b 100644
--- a/Scripts/Impostors.cs
+++ b/Scripts/Impostors.cs
@@ -492,7 +492,7 @@ public class Impostors : MonoBehaviour
       impostorObject = GameObject.CreatePrimitive(PrimitiveType.Quad);
       impostorObject.name = "Impostor";
       impostorObject.transform.SetParent(transform, false);
-      impostorObject.transform.localScale = Vector3.one * sphere_radius_ * 2f;
+      impostorObject.transform.localScale = Vector3.one;
       DestroyImmediate(impostorObject.GetComponent<Collider>());
       impostorObject.GetComponent<MeshRenderer>().sharedMaterial = impostorMaterial;
 
@@ -551,4 +551,3 @@ public class ImpostorsEditor : Editor
   }
 }
 #endif  // UNITY_EDITOR
-
diff --git a/impostor.cginc b/impostor.cginc
index 8cf306f..b49dfce 100644
--- a/impostor.cginc
+++ b/impostor.cginc
@@ -84,6 +84,7 @@ struct ImpostorResult {
     float3 normal;
     float metallic;
     float smoothness;
+    float3 objPos;
 };
 
 float SampleImpostorDepthCell(float2 cell, float2 uvInCell, float gridRes) {
@@ -134,6 +135,23 @@ 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) {
+    float3 planeX, planeY, planeN;
+    FrameBasis(frameDir, planeX, planeY, planeN);
+
+    // Invert VirtualPlaneUV: offset = 0.5 - uv, scale by diameter
+    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;
+
+    return offsetXY.x * planeX + offsetXY.y * planeY + offsetZ * planeN;
+}
+
 ImpostorSample BlendImpostorSamples(ImpostorSample s0, ImpostorSample s1, ImpostorSample s2, float3 bw) {
     ImpostorSample result;
     float3 alpha = float3(s0.albedo.a, s1.albedo.a, s2.albedo.a);
@@ -155,25 +173,22 @@ ImpostorSample BlendImpostorSamples(ImpostorSample s0, ImpostorSample s1, Impost
 }
 
 // Billboard vertex transformation for impostors
-void impostor_vert(float4 vertexOS, inout float3 worldPos) {
+void impostor_vert(inout float3 vertexOS) {
     float3 center = mul(unity_ObjectToWorld, float4(0,0,0,1)).xyz;
 
-    float3 scale = float3(
-        length(unity_ObjectToWorld._m00_m10_m20),
-        length(unity_ObjectToWorld._m01_m11_m21),
-        length(unity_ObjectToWorld._m02_m12_m22));
-
 #ifdef SHADOW_CASTER_PASS
     float3 camPos = _Impostors_Main_Camera_Pos;
 #else
     float3 camPos = _WorldSpaceCameraPos;
 #endif
 
-    // Billboard facing the camera direction
+    // Billboard facing the camera direction (world space, then convert back to object space).
     float3 viewWS = normalize(camPos - center);
     float3 right, up;
     BillboardBasis(viewWS, right, up);
-    worldPos = center + vertexOS.x * right * scale.x + vertexOS.y * up * scale.y;
+    float radiusScale = _Impostors_Sphere_Radius * 2.0;
+    float3 worldPos = center + vertexOS.x * right * radiusScale + vertexOS.y * up * radiusScale;
+    vertexOS = mul(unity_WorldToObject, float4(worldPos, 1)).xyz;
 }
 
 // Sample impostor atlas with view-dependent blending
@@ -191,11 +206,7 @@ ImpostorResult impostor_frag(float3 worldPos) {
 #endif
     float3 viewDir = normalize(worldPos - camPos);
 
-    float3 scale = float3(
-        length(unity_ObjectToWorld._m00_m10_m20),
-        length(unity_ObjectToWorld._m01_m11_m21),
-        length(unity_ObjectToWorld._m02_m12_m22));
-    float radiusWS = _Impostors_Sphere_Radius * max(scale.x, max(scale.y, scale.z));
+    float radiusWS = _Impostors_Sphere_Radius;
 
     float3 originToRo = camPos - center;
     float b = dot(originToRo, viewDir);
@@ -259,15 +270,28 @@ ImpostorResult impostor_frag(float3 worldPos) {
         uv2 = uvBase2 + ImpostorParallaxOffsetForFrame(frameDir2, pivotToCamOS, uvBase2, depthBlended) * parallaxStrength;
     }
 
-    ImpostorSample s0 = SampleImpostorCell(cell0, uv0, gridRes);
-    ImpostorSample s1 = SampleImpostorCell(cell1, uv1, gridRes);
-    ImpostorSample s2 = SampleImpostorCell(cell2, uv2, gridRes);
+    float2 uv0Final = uv0;
+    float2 uv1Final = uv1;
+    float2 uv2Final = uv2;
+
+    ImpostorSample s0 = SampleImpostorCell(cell0, uv0Final, gridRes);
+    ImpostorSample s1 = SampleImpostorCell(cell1, uv1Final, gridRes);
+    ImpostorSample s2 = SampleImpostorCell(cell2, uv2Final, gridRes);
 
     // Parallax can push UVs into transparent pixels at silhouettes; fall back to unshifted UVs when that happens.
     if (parallaxStrength > 0.001) {
-        if (s0.albedo.a < _Impostors_Cutoff && baseAlpha0 > _Impostors_Cutoff) s0 = SampleImpostorCell(cell0, uvBase0, gridRes);
-        if (s1.albedo.a < _Impostors_Cutoff && baseAlpha1 > _Impostors_Cutoff) s1 = SampleImpostorCell(cell1, uvBase1, gridRes);
-        if (s2.albedo.a < _Impostors_Cutoff && baseAlpha2 > _Impostors_Cutoff) s2 = SampleImpostorCell(cell2, uvBase2, gridRes);
+        if (s0.albedo.a < _Impostors_Cutoff && baseAlpha0 > _Impostors_Cutoff) {
+            uv0Final = uvBase0;
+            s0 = SampleImpostorCell(cell0, uv0Final, gridRes);
+        }
+        if (s1.albedo.a < _Impostors_Cutoff && baseAlpha1 > _Impostors_Cutoff) {
+            uv1Final = uvBase1;
+            s1 = SampleImpostorCell(cell1, uv1Final, gridRes);
+        }
+        if (s2.albedo.a < _Impostors_Cutoff && baseAlpha2 > _Impostors_Cutoff) {
+            uv2Final = uvBase2;
+            s2 = SampleImpostorCell(cell2, uv2Final, gridRes);
+        }
     }
 
     // Blend 3 samples
@@ -286,6 +310,17 @@ 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).
+    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;
+
     return result;
 }
 
diff --git a/pbr.cginc b/pbr.cginc
index 6a14655..2aa6be7 100644
--- a/pbr.cginc
+++ b/pbr.cginc
@@ -24,6 +24,9 @@ struct Pbr {
   float cl_strength;
   float3 cl_color;
 #endif
+#if defined(_IMPOSTORS)
+  float3 objPos;
+#endif
 };
 
 #define MIN_PERCEPTUAL_ROUGHNESS 5e-2f
@@ -166,6 +169,7 @@ Pbr getPbr(v2f i) {
   pbr.normal = imp.normal;
   pbr.smoothness = imp.smoothness;
   pbr.metallic = imp.metallic;
+  pbr.objPos = imp.objPos;
 #else
   pbr.albedo = _MainTex.Sample(aniso16_trilinear_repeat_s, uv_parallax * _MainTex_ST.xy + _MainTex_ST.zw);
   pbr.albedo *= _Color;