Impostors: add ray-sphere intersection test

1 files changed, 88 insertions, 57 deletions

diff --git a/impostor.cginc b/impostor.cginc
index a60c9ca..bb4c38f 100644
--- a/impostor.cginc
+++ b/impostor.cginc
@@ -8,6 +8,7 @@ SamplerState bilinear_clamp_s;
 Texture2D _ImpostorAtlas;
 int _GridResolution;
 float _Cutoff;
+float _SphereRadius;
 float3 _ImpostorMainCameraPos;
 
 #ifndef IMPOSTOR_SHADOW_PASS
@@ -97,13 +98,8 @@ struct v2f {
     float4 pos : SV_POSITION;
     UNITY_FOG_COORDS(7)
 #endif
-    float2 uv1 : TEXCOORD1;
-    float2 uv2 : TEXCOORD2;
-    float2 uv3 : TEXCOORD3;
-    nointerpolation float2 cell1 : TEXCOORD4;
-    nointerpolation float2 cell2 : TEXCOORD5;
-    nointerpolation float2 cell3 : TEXCOORD6;
-    nointerpolation float3 blendWeights : TEXCOORD8;
+    float3 worldPos : TEXCOORD1;
+    float3 centerPos : TEXCOORD2;
     UNITY_VERTEX_OUTPUT_STEREO
 };
 
@@ -113,6 +109,7 @@ v2f vert(appdata v) {
     UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(o);
 
     float3 center = mul(unity_ObjectToWorld, float4(0,0,0,1)).xyz;
+    o.centerPos = center;
     float3 scale = float3(
         length(unity_ObjectToWorld._m00_m10_m20),
         length(unity_ObjectToWorld._m01_m11_m21),
@@ -124,38 +121,12 @@ v2f vert(appdata v) {
     float3 camPos = _WorldSpaceCameraPos;
 #endif
 
-    // View direction in object space
-    float3 viewOS = normalize(mul((float3x3)unity_WorldToObject, normalize(camPos - center)));
-
-    // Get continuous grid position and find the 3 frames
-    float gridRes = (float)_GridResolution;
-    float2 grid = GridFromDir(viewOS, gridRes);
-    float2 gridFloor = floor(grid);
-    float2 gridFrac = frac(grid);
-
-    // Compute barycentric weights and determine which triangle
-    float4 bary = GridCellBarycentric(gridFrac);
-    o.blendWeights = bary.xyz;
-
-    // Frame 1: (0,0) corner of cell
-    o.cell1 = gridFloor;
-
-    // Frame 2: (0,1) or (1,0) corner depending on which triangle
-    o.cell2 = clamp(gridFloor + lerp(float2(0,1), float2(1,0), bary.w), 0, gridRes - 1);
-
-    // Frame 3: (1,1) corner of cell
-    o.cell3 = clamp(gridFloor + float2(1,1), 0, gridRes - 1);
-
-    // Get directions for each frame
-    float3 dir1 = DirFromCell(o.cell1, gridRes);
-    float3 dir2 = DirFromCell(o.cell2, gridRes);
-    float3 dir3 = DirFromCell(o.cell3, gridRes);
-
     // Billboard facing the camera direction
     float3 viewWS = normalize(camPos - center);
     float3 right, up;
     BillboardBasis(viewWS, right, up);
     float3 worldPos = center + v.vertex.x * right * scale.x + v.vertex.y * up * scale.y;
+    o.worldPos = worldPos;
 
 #ifdef IMPOSTOR_SHADOW_PASS
     v.vertex = mul(unity_WorldToObject, float4(worldPos, 1));
@@ -166,43 +137,103 @@ v2f vert(appdata v) {
     UNITY_TRANSFER_FOG(o, o.pos);
 #endif
 
-    // Compute virtual plane UVs for all 3 frames
-    float3 pivotToCamOS = mul((float3x3)unity_WorldToObject, camPos - center) * 100.0;
-    float3 vertexPosOS = mul((float3x3)unity_WorldToObject, worldPos - center);
-    float3 vertexToCamOS = pivotToCamOS - vertexPosOS;
-
-    o.uv1 = VirtualPlaneUV(dir1, pivotToCamOS, vertexToCamOS, 0.5);
-    o.uv2 = VirtualPlaneUV(dir2, pivotToCamOS, vertexToCamOS, 0.5);
-    o.uv3 = VirtualPlaneUV(dir3, pivotToCamOS, vertexToCamOS, 0.5);
-
     return o;
 }
 
-float4 BlendFrames(v2f i) {
-    float4 s1 = SampleAtlas(i.uv1, i.cell1);
-    float4 s2 = SampleAtlas(i.uv2, i.cell2);
-    float4 s3 = SampleAtlas(i.uv3, i.cell3);
-    return s1 * i.blendWeights.x + s2 * i.blendWeights.y + s3 * i.blendWeights.z;
+// General purpose ray-sphere intersection.
+bool raySphereIntersect(
+    float3 ro, float3 rayDir,
+    float3 origin, float radius,
+    out float3 posNear, out float3 posFar) {
+  float3 originToRo = ro - origin;
+
+  float b = dot(originToRo, rayDir);
+  float c = dot(originToRo, originToRo) - radius * radius;
+  float disc = b * b - c;
+
+  if (disc < 0) {
+    return false;
+  }
+
+  float t_near = -b - sqrt(disc);
+  float t_far  = -b + sqrt(disc);
+
+  posNear = ro + rayDir * t_near;
+  posFar  = ro + rayDir * t_far;
+
+  return true;
 }
 
-#ifdef IMPOSTOR_SHADOW_PASS
 float4 frag(v2f i) : SV_Target {
-    float4 col = BlendFrames(i);
-    clip(col.a - _Cutoff);
-    SHADOW_CASTER_FRAGMENT(i)
-}
+    // Sphere culling first
+    float3 eyeVec = i.worldPos - _WorldSpaceCameraPos;
+    float3 viewDir = normalize(eyeVec);
+    float3 posNear, posFar;
+    bool didIntersect = raySphereIntersect(
+        _WorldSpaceCameraPos, viewDir,
+        i.centerPos, _SphereRadius,
+        posNear, posFar);
+    clip(didIntersect - 0.5);
+
+    // Camera position for grid computation (matches billboard orientation)
+#ifdef IMPOSTOR_SHADOW_PASS
+    float3 camPos = _ImpostorMainCameraPos;
 #else
-float4 frag(v2f i) : SV_Target {
-    float4 col = BlendFrames(i);
+    float3 camPos = _WorldSpaceCameraPos;
+#endif
+    float3 center = i.centerPos;
+
+    // View direction in object space
+    float3 viewOS = normalize(mul((float3x3)unity_WorldToObject, normalize(camPos - center)));
+
+    // Get continuous grid position and find the 3 frames
+    float gridRes = (float)_GridResolution;
+    float2 grid = GridFromDir(viewOS, gridRes);
+    float2 gridFloor = floor(grid);
+    float2 gridFrac = frac(grid);
+
+    // Compute barycentric weights and determine which triangle
+    float4 bary = GridCellBarycentric(gridFrac);
+    float3 blendWeights = bary.xyz;
 
+    // Frame cells
+    float2 cell1 = gridFloor;
+    float2 cell2 = clamp(gridFloor + lerp(float2(0,1), float2(1,0), bary.w), 0, gridRes - 1);
+    float2 cell3 = clamp(gridFloor + float2(1,1), 0, gridRes - 1);
+
+    // Get directions for each frame
+    float3 dir1 = DirFromCell(cell1, gridRes);
+    float3 dir2 = DirFromCell(cell2, gridRes);
+    float3 dir3 = DirFromCell(cell3, gridRes);
+
+    // Compute virtual plane UVs for all 3 frames
+    float3 pivotToCamOS = mul((float3x3)unity_WorldToObject, camPos - center) * 100.0;
+    float3 vertexPosOS = mul((float3x3)unity_WorldToObject, i.worldPos - center);
+    float3 vertexToCamOS = pivotToCamOS - vertexPosOS;
+
+    float2 uv1 = VirtualPlaneUV(dir1, pivotToCamOS, vertexToCamOS, 0.5);
+    float2 uv2 = VirtualPlaneUV(dir2, pivotToCamOS, vertexToCamOS, 0.5);
+    float2 uv3 = VirtualPlaneUV(dir3, pivotToCamOS, vertexToCamOS, 0.5);
+
+    // Sample and blend frames
+    float4 s1 = SampleAtlas(uv1, cell1);
+    float4 s2 = SampleAtlas(uv2, cell2);
+    float4 s3 = SampleAtlas(uv3, cell3);
+    float4 col = s1 * blendWeights.x + s2 * blendWeights.y + s3 * blendWeights.z;
+
+#ifndef IMPOSTOR_SHADOW_PASS
     if (_DebugMode > 0.5)
-        return float4(i.blendWeights.xy, 0, 1);
+        return float4(blendWeights.xy, 0, 1);
+#endif
 
     col *= _Color;
     clip(col.a - _Cutoff);
+#ifdef IMPOSTOR_SHADOW_PASS
+    SHADOW_CASTER_FRAGMENT(i)
+#else
     UNITY_APPLY_FOG(i.fogCoord, col);
     return col;
-}
 #endif
+}
 
 #endif