feat: mip sampling

1 files changed, 46 insertions, 20 deletions

diff --git a/assets/shaders/geodesic.slang b/assets/shaders/geodesic.slang
index db450a8..a1b0f46 100644
--- a/assets/shaders/geodesic.slang
+++ b/assets/shaders/geodesic.slang
@@ -78,11 +78,6 @@ struct Hit
     float  hitRadius;
 };
 
-float3 SampleHDRI(float3 direction)
-{
-    return u_HDRIEnvironment.Sample(direction).rgb;
-}
-
 float hash(float3 p)
 {
     p = frac(p * float3(0.1031, 0.1030, 0.0973));
@@ -280,6 +275,11 @@ void RK4Step(inout Ray ray, float dL)
 float CalculateAdaptiveStepSize(Ray ray, float baseStepSize)
 {
     float step = 0.02 * max(ray.r - R_PHOTON, 0.0);
+
+    float rc = length(float2(ray.x, ray.z));
+    if (rc < disk.disk_r2 * 3.0 && abs(ray.y) < disk.thickness * 8.0)
+        step = min(step, disk.thickness);
+
     return clamp(step, MIN_STEP_SIZE, MAX_STEP_SIZE);
 }
 
@@ -288,11 +288,10 @@ float3 ACESFilm(float3 x)
     return clamp((x * (2.51 * x + 0.03)) / (x * (2.43 * x + 0.59) + 0.14), 0.0, 1.0);
 }
 
-[shader("fragment")]
-float4 fragmentMain(VSOutput input) : SV_Target
+float3 TracePixel(float2 texCoord)
 {
-    float u = (2.0 * input.texCoord.x - 1.0) * cam.aspect * cam.tanHalfFov;
-    float v = (1.0 - 2.0 * input.texCoord.y) * cam.tanHalfFov;
+    float u = (2.0 * texCoord.x - 1.0) * cam.aspect * cam.tanHalfFov;
+    float v = (1.0 - 2.0 * texCoord.y) * cam.tanHalfFov;
     float3 dir = normalize(u * cam.camRight - v * cam.camUp + cam.camForward);
     Ray ray = InitRay(cam.camPos, dir);
 
@@ -323,16 +322,22 @@ float4 fragmentMain(VSOutput input) : SV_Target
         RK4Step(ray, stepSize);
         float3 newPos = float3(ray.x, ray.y, ray.z);
 
-        if (prevPos.y * newPos.y < 0.0)
         {
-            float  t     = prevPos.y / (prevPos.y - newPos.y);
-            float3 cross = lerp(prevPos, newPos, t);
-            float  rc    = length(float2(cross.x, cross.z));
-            if (rc >= max(disk.disk_r1, R_ISCO) && rc <= disk.disk_r2)
+            float H       = disk.thickness;
+            bool  crossed = prevPos.y * newPos.y < 0.0;
+            bool  inSlab  = abs(newPos.y) <= H;
+            if (crossed || inSlab)
             {
-                diskColor = DiskEmission(cross, newPos - prevPos);
-                hitDisk   = true;
-                break;
+                float3 hitP = crossed
+                    ? lerp(prevPos, newPos, prevPos.y / (prevPos.y - newPos.y))
+                    : newPos;
+                float rc = length(float2(hitP.x, hitP.z));
+                if (rc >= max(disk.disk_r1, R_ISCO) && rc <= disk.disk_r2)
+                {
+                    diskColor = DiskEmission(hitP, newPos - prevPos);
+                    hitDisk   = true;
+                    break;
+                }
             }
         }
 
@@ -341,6 +346,10 @@ float4 fragmentMain(VSOutput input) : SV_Target
         if (ray.dr > 0.0 && ray.r > 50.0 * SagA_rs) break;
     }
 
+    float3 rayDir    = normalize(float3(ray.x, ray.y, ray.z) - cam.camPos);
+    float  footprint = max(length(ddx(rayDir)), length(ddy(rayDir)));
+    float  envLod    = clamp(log2(max(footprint / 0.0015, 1.0)), 0.0, 10.0);
+
     float3 shade;
     if (hitDisk)
     {
@@ -360,9 +369,26 @@ float4 fragmentMain(VSOutput input) : SV_Target
     }
     else
     {
-        float3 rayDir = normalize(float3(ray.x, ray.y, ray.z) - cam.camPos);
-        shade = SampleHDRI(rayDir);
+        shade = u_HDRIEnvironment.SampleLevel(rayDir, envLod).rgb;
     }
 
-    return float4(ACESFilm(shade), 1.0);
+    return shade;
+}
+
+[shader("fragment")]
+float4 fragmentMain(VSOutput input) : SV_Target
+{
+    if (cam.moving)
+        return float4(ACESFilm(TracePixel(input.texCoord)), 1.0);
+
+    float2 dUV = float2(ddx(input.texCoord.x), ddy(input.texCoord.y));
+    float2 offs[4] = {
+        float2( 0.125,  0.375), float2( 0.375, -0.125),
+        float2(-0.125, -0.375), float2(-0.375,  0.125),
+    };
+    float3 sum = float3(0.0);
+    for (int i = 0; i < 4; ++i)
+        sum += TracePixel(input.texCoord + offs[i] * dUV);
+
+    return float4(ACESFilm(sum * 0.25), 1.0);
 }