Fix incorrect meshlight pdf (ref only)

sergcpp · Sep 1, 2024 · 320cf29 · 320cf29
1 parent 3aabc46
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Showing 3 changed files with 69 additions and 68 deletions.
diff --git a/internal/CoreRef.cpp b/internal/CoreRef.cpp
@@ -1164,67 +1164,6 @@ force_inline float angle_between(const fvec4 &v1, const fvec4 &v2) {
     }
 }
 
-// "Stratified Sampling of Spherical Triangles" https://www.graphics.cornell.edu/pubs/1995/Arv95c.pdf
-// Based on https://www.shadertoy.com/view/4tGGzd
-float SampleSphericalTriangle(const fvec4 &P, const fvec4 &p1, const fvec4 &p2, const fvec4 &p3, const fvec2 Xi,
-                              fvec4 *out_dir) {
-    // Setup spherical triangle
-    const fvec4 A = normalize(p1 - P), B = normalize(p2 - P), C = normalize(p3 - P);
-
-    // calculate internal angles of spherical triangle: alpha, beta and gamma
-    const fvec4 BA = orthogonalize(A, B - A);
-    const fvec4 CA = orthogonalize(A, C - A);
-    const fvec4 AB = orthogonalize(B, A - B);
-    const fvec4 CB = orthogonalize(B, C - B);
-    const fvec4 BC = orthogonalize(C, B - C);
-    const fvec4 AC = orthogonalize(C, A - C);
-
-    const float alpha = angle_between(BA, CA);
-    const float beta = angle_between(AB, CB);
-    const float gamma = angle_between(BC, AC);
-
-    const float area = alpha + beta + gamma - PI;
-    if (area <= SPHERICAL_AREA_THRESHOLD) {
-        return 0.0f;
-    }
-
-    if (out_dir) {
-        // calculate arc lengths for edges of spherical triangle
-        // const float a = portable_acosf(clamp(dot(B, C), -1.0f, 1.0f));
-        const float b = portable_acosf(clamp(dot(C, A), -1.0f, 1.0f));
-        const float c = portable_acosf(clamp(dot(A, B), -1.0f, 1.0f));
-
-        // Use one random variable to select the new area
-        const float area_S = Xi.get<0>() * area;
-
-        // Save the sine and cosine of the angle delta
-        const float p = sinf(area_S - alpha);
-        const float q = cosf(area_S - alpha);
-
-        // Compute the pair(u; v) that determines sin(beta_s) and cos(beta_s)
-        const float u = q - cosf(alpha);
-        const float v = p + sinf(alpha) * cosf(c);
-
-        // Compute the s coordinate as normalized arc length from A to C_s
-        const float denom = ((v * p + u * q) * sinf(alpha));
-        const float s =
-            (1.0f / b) * portable_acosf(clamp(safe_div(((v * q - u * p) * cosf(alpha) - v), denom), -1.0f, 1.0f));
-
-        // Compute the third vertex of the sub - triangle
-        const fvec4 C_s = slerp(A, C, s);
-
-        // Compute the t coordinate using C_s and Xi[1]
-        const float denom2 = portable_acosf(clamp(dot(C_s, B), -1.0f, 1.0f));
-        const float t = safe_div(portable_acosf(clamp(1.0f - Xi.get<1>() * (1.0f - dot(C_s, B)), -1.0f, 1.0f)), denom2);
-
-        // Construct the corresponding point on the sphere.
-        (*out_dir) = slerp(B, C_s, t);
-    }
-
-    // return pdf
-    return (1.0f / area);
-}
-
 } // namespace Ref
 } // namespace Ray
 
@@ -1296,6 +1235,67 @@ float Ray::Ref::SampleSphericalRectangle(const fvec4 &P, const fvec4 &light_pos,
     return (1.0f / area);
 }
 
+// "Stratified Sampling of Spherical Triangles" https://www.graphics.cornell.edu/pubs/1995/Arv95c.pdf
+// Based on https://www.shadertoy.com/view/4tGGzd
+float Ray::Ref::SampleSphericalTriangle(const fvec4 &P, const fvec4 &p1, const fvec4 &p2, const fvec4 &p3,
+                                        const fvec2 Xi, fvec4 *out_dir) {
+    // Setup spherical triangle
+    const fvec4 A = normalize(p1 - P), B = normalize(p2 - P), C = normalize(p3 - P);
+
+    // calculate internal angles of spherical triangle: alpha, beta and gamma
+    const fvec4 BA = orthogonalize(A, B - A);
+    const fvec4 CA = orthogonalize(A, C - A);
+    const fvec4 AB = orthogonalize(B, A - B);
+    const fvec4 CB = orthogonalize(B, C - B);
+    const fvec4 BC = orthogonalize(C, B - C);
+    const fvec4 AC = orthogonalize(C, A - C);
+
+    const float alpha = angle_between(BA, CA);
+    const float beta = angle_between(AB, CB);
+    const float gamma = angle_between(BC, AC);
+
+    const float area = alpha + beta + gamma - PI;
+    if (area <= SPHERICAL_AREA_THRESHOLD) {
+        return 0.0f;
+    }
+
+    if (out_dir) {
+        // calculate arc lengths for edges of spherical triangle
+        // const float a = portable_acosf(clamp(dot(B, C), -1.0f, 1.0f));
+        const float b = portable_acosf(clamp(dot(C, A), -1.0f, 1.0f));
+        const float c = portable_acosf(clamp(dot(A, B), -1.0f, 1.0f));
+
+        // Use one random variable to select the new area
+        const float area_S = Xi.get<0>() * area;
+
+        // Save the sine and cosine of the angle delta
+        const float p = sinf(area_S - alpha);
+        const float q = cosf(area_S - alpha);
+
+        // Compute the pair(u; v) that determines sin(beta_s) and cos(beta_s)
+        const float u = q - cosf(alpha);
+        const float v = p + sinf(alpha) * cosf(c);
+
+        // Compute the s coordinate as normalized arc length from A to C_s
+        const float denom = ((v * p + u * q) * sinf(alpha));
+        const float s =
+            (1.0f / b) * portable_acosf(clamp(safe_div(((v * q - u * p) * cosf(alpha) - v), denom), -1.0f, 1.0f));
+
+        // Compute the third vertex of the sub - triangle
+        const fvec4 C_s = slerp(A, C, s);
+
+        // Compute the t coordinate using C_s and Xi[1]
+        const float denom2 = portable_acosf(clamp(dot(C_s, B), -1.0f, 1.0f));
+        const float t = safe_div(portable_acosf(clamp(1.0f - Xi.get<1>() * (1.0f - dot(C_s, B)), -1.0f, 1.0f)), denom2);
+
+        // Construct the corresponding point on the sphere.
+        (*out_dir) = slerp(B, C_s, t);
+    }
+
+    // return pdf
+    return (1.0f / area);
+}
+
 Ray::Ref::fvec2 Ray::Ref::get_scrambled_2d_rand(const uint32_t dim, const uint32_t seed, const int sample,
                                                 const uint32_t rand_seq[]) {
     const uint32_t shuffled_dim = nested_uniform_scramble_base2(dim, seed) & (RAND_DIMS_COUNT - 1);

diff --git a/internal/CoreRef.h b/internal/CoreRef.h
@@ -306,6 +306,8 @@ fvec2 get_scrambled_2d_rand(const uint32_t dim, const uint32_t seed, const int s
 
 float SampleSphericalRectangle(const fvec4 &P, const fvec4 &light_pos, const fvec4 &axis_u, const fvec4 &axis_v,
                                fvec2 Xi, fvec4 *out_p);
+float SampleSphericalTriangle(const fvec4 &P, const fvec4 &p1, const fvec4 &p2, const fvec4 &p3, const fvec2 Xi,
+                              fvec4 *out_dir);
 
 // Generation of rays
 void GeneratePrimaryRays(const camera_t &cam, const rect_t &r, int w, int h, const uint32_t rand_seq[],

diff --git a/internal/ShadeRef.cpp b/internal/ShadeRef.cpp
@@ -1504,13 +1504,12 @@ Ray::color_rgba_t Ray::Ref::ShadeSurface(const pass_settings_t &ps, const float
 
             const float cos_theta = fabsf(dot(I, light_forward)); // abs for doublesided light
             if (cos_theta > 0.0f) {
-                float light_pdf;
-#if USE_SPHERICAL_AREA_LIGHT_SAMPLING
-                const fvec4 P = TransformPoint(ro, mi->inv_xform);
-                light_pdf = SampleSphericalTriangle(P, p1, p2, p3, {}, nullptr) / pdf_factor;
-                if (light_pdf == 0.0f)
-#endif
-                {
+                float light_pdf = 0.0f;
+                if (USE_SPHERICAL_AREA_LIGHT_SAMPLING) {
+                    const fvec4 P = TransformPoint(ro, mi->inv_xform);
+                    light_pdf = SampleSphericalTriangle(P, p1, p2, p3, {}, nullptr) / pdf_factor;
+                }
+                if (light_pdf == 0.0f) {
                     light_pdf = (inter.t * inter.t) / (tri_area * cos_theta * pdf_factor);
                 }