Brecht Van Lommel
79f1cc601c
Detect cases where a ray-intersection would miss the current triangle, which if the intersection is strictly watertight, implies that a neighboring triangle would incorrectly be hit instead. When that is detected, apply a ray-offset. The idea being that we only want to introduce potential error from ray offsets if we really need to. This work for BVH2 and Embree, as we are able to match the ray-interesction bit-for-bit, though doing so for Embree requires ugly hacks. Tiny differences like fused-multiply-add or dot product intrinstics in matrix inversion and ray intersection needed to be matched exactly, so this is fragile. Unfortunately we're not able to do the same for OptiX or MetalRT, since those implementations are unknown (and possibly impossible to match as hardware instructions). Still artifacts are much reduced, though not eliminated. Ref T97259 Differential Revision: https://developer.blender.org/D15559
303 lines
10 KiB
C++
303 lines
10 KiB
C++
/* SPDX-License-Identifier: Apache-2.0
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* Copyright 2011-2022 Blender Foundation */
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#ifndef __UTIL_MATH_INTERSECT_H__
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#define __UTIL_MATH_INTERSECT_H__
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CCL_NAMESPACE_BEGIN
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/* Ray Intersection */
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ccl_device bool ray_sphere_intersect(float3 ray_P,
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float3 ray_D,
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float ray_tmin,
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float ray_tmax,
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float3 sphere_P,
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float sphere_radius,
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ccl_private float3 *isect_P,
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ccl_private float *isect_t)
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{
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const float3 d = sphere_P - ray_P;
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const float radiussq = sphere_radius * sphere_radius;
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const float tsq = dot(d, d);
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if (tsq > radiussq) {
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/* Ray origin outside sphere. */
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const float tp = dot(d, ray_D);
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if (tp < 0.0f) {
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/* Ray points away from sphere. */
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return false;
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}
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const float dsq = tsq - tp * tp; /* Pythagoras. */
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if (dsq > radiussq) {
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/* Closest point on ray outside sphere. */
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return false;
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}
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const float t = tp - sqrtf(radiussq - dsq); /* pythagoras */
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if (t > ray_tmin && t < ray_tmax) {
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*isect_t = t;
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*isect_P = ray_P + ray_D * t;
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return true;
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}
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}
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return false;
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}
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ccl_device bool ray_aligned_disk_intersect(float3 ray_P,
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float3 ray_D,
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float ray_tmin,
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float ray_tmax,
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float3 disk_P,
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float disk_radius,
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ccl_private float3 *isect_P,
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ccl_private float *isect_t)
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{
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/* Aligned disk normal. */
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float disk_t;
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const float3 disk_N = normalize_len(ray_P - disk_P, &disk_t);
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const float div = dot(ray_D, disk_N);
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if (UNLIKELY(div == 0.0f)) {
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return false;
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}
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/* Compute t to intersection point. */
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const float t = -disk_t / div;
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if (!(t > ray_tmin && t < ray_tmax)) {
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return false;
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}
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/* Test if within radius. */
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float3 P = ray_P + ray_D * t;
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if (len_squared(P - disk_P) > disk_radius * disk_radius) {
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return false;
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}
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*isect_P = P;
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*isect_t = t;
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return true;
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}
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ccl_device bool ray_disk_intersect(float3 ray_P,
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float3 ray_D,
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float ray_tmin,
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float ray_tmax,
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float3 disk_P,
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float3 disk_N,
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float disk_radius,
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ccl_private float3 *isect_P,
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ccl_private float *isect_t)
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{
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const float3 vp = ray_P - disk_P;
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const float dp = dot(vp, disk_N);
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const float cos_angle = dot(disk_N, -ray_D);
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if (dp * cos_angle > 0.f) // front of light
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{
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float t = dp / cos_angle;
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if (t < 0.f) { /* Ray points away from the light. */
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return false;
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}
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float3 P = ray_P + t * ray_D;
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float3 T = P - disk_P;
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if (dot(T, T) < sqr(disk_radius) && (t > ray_tmin && t < ray_tmax)) {
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*isect_P = ray_P + t * ray_D;
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*isect_t = t;
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return true;
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}
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}
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return false;
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}
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/* Custom rcp, cross and dot implementations that match Embree bit for bit. */
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ccl_device_forceinline float ray_triangle_rcp(const float x)
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{
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#ifdef __KERNEL_NEON__
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/* Move scalar to vector register and do rcp. */
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__m128 a;
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a[0] = x;
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float32x4_t reciprocal = vrecpeq_f32(a);
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reciprocal = vmulq_f32(vrecpsq_f32(a, reciprocal), reciprocal);
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reciprocal = vmulq_f32(vrecpsq_f32(a, reciprocal), reciprocal);
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return reciprocal[0];
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#elif defined(__KERNEL_SSE__)
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const __m128 a = _mm_set_ss(x);
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const __m128 r = _mm_rcp_ss(a);
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# ifdef __KERNEL_AVX2_
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return _mm_cvtss_f32(_mm_mul_ss(r, _mm_fnmadd_ss(r, a, _mm_set_ss(2.0f))));
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# else
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return _mm_cvtss_f32(_mm_mul_ss(r, _mm_sub_ss(_mm_set_ss(2.0f), _mm_mul_ss(r, a))));
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# endif
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#else
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return 1.0f / x;
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#endif
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}
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ccl_device_inline float ray_triangle_dot(const float3 a, const float3 b)
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{
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#if defined(__KERNEL_SSE41__) && defined(__KERNEL_SSE__)
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return madd(ssef(a.x), ssef(b.x), madd(ssef(a.y), ssef(b.y), ssef(a.z) * ssef(b.z)))[0];
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#else
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return a.x * b.x + a.y * b.y + a.z * b.z;
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#endif
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}
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ccl_device_inline float3 ray_triangle_cross(const float3 a, const float3 b)
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{
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#if defined(__KERNEL_SSE41__) && defined(__KERNEL_SSE__)
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return make_float3(msub(ssef(a.y), ssef(b.z), ssef(a.z) * ssef(b.y))[0],
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msub(ssef(a.z), ssef(b.x), ssef(a.x) * ssef(b.z))[0],
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msub(ssef(a.x), ssef(b.y), ssef(a.y) * ssef(b.x))[0]);
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#else
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return make_float3(a.y * b.z - a.z * b.y, a.z * b.x - a.x * b.z, a.x * b.y - a.y * b.x);
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#endif
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}
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ccl_device_forceinline bool ray_triangle_intersect(const float3 ray_P,
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const float3 ray_D,
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const float ray_tmin,
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const float ray_tmax,
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const float3 tri_a,
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const float3 tri_b,
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const float3 tri_c,
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ccl_private float *isect_u,
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ccl_private float *isect_v,
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ccl_private float *isect_t)
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{
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/* This implementation matches the Plücker coordinates triangle intersection
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* in Embree. */
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/* Calculate vertices relative to ray origin. */
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const float3 v0 = tri_a - ray_P;
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const float3 v1 = tri_b - ray_P;
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const float3 v2 = tri_c - ray_P;
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/* Calculate triangle edges. */
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const float3 e0 = v2 - v0;
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const float3 e1 = v0 - v1;
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const float3 e2 = v1 - v2;
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/* Perform edge tests. */
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const float U = ray_triangle_dot(ray_triangle_cross(e0, v2 + v0), ray_D);
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const float V = ray_triangle_dot(ray_triangle_cross(e1, v0 + v1), ray_D);
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const float W = ray_triangle_dot(ray_triangle_cross(e2, v1 + v2), ray_D);
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const float UVW = U + V + W;
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const float eps = FLT_EPSILON * fabsf(UVW);
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const float minUVW = min(U, min(V, W));
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const float maxUVW = max(U, max(V, W));
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if (!(minUVW >= -eps || maxUVW <= eps)) {
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return false;
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}
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/* Calculate geometry normal and denominator. */
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const float3 Ng1 = ray_triangle_cross(e1, e0);
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const float3 Ng = Ng1 + Ng1;
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const float den = dot(Ng, ray_D);
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/* Avoid division by 0. */
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if (UNLIKELY(den == 0.0f)) {
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return false;
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}
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/* Perform depth test. */
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const float T = dot(v0, Ng);
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const float t = T / den;
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if (!(t >= ray_tmin && t <= ray_tmax)) {
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return false;
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}
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const float rcp_uvw = (fabsf(UVW) < 1e-18f) ? 0.0f : ray_triangle_rcp(UVW);
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*isect_u = min(U * rcp_uvw, 1.0f);
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*isect_v = min(V * rcp_uvw, 1.0f);
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*isect_t = t;
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return true;
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}
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ccl_device_forceinline bool ray_triangle_intersect_self(const float3 ray_P,
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const float3 ray_D,
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const float3 tri_a,
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const float3 tri_b,
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const float3 tri_c)
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{
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/* Matches logic in ray_triangle_intersect, self intersection test to validate
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* if a ray is going to hit self or might incorrectly hit a neighboring triangle. */
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/* Calculate vertices relative to ray origin. */
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const float3 v0 = tri_a - ray_P;
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const float3 v1 = tri_b - ray_P;
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const float3 v2 = tri_c - ray_P;
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/* Calculate triangle edges. */
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const float3 e0 = v2 - v0;
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const float3 e1 = v0 - v1;
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const float3 e2 = v1 - v2;
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/* Perform edge tests. */
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const float U = ray_triangle_dot(ray_triangle_cross(v2 + v0, e0), ray_D);
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const float V = ray_triangle_dot(ray_triangle_cross(v0 + v1, e1), ray_D);
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const float W = ray_triangle_dot(ray_triangle_cross(v1 + v2, e2), ray_D);
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const float eps = FLT_EPSILON * fabsf(U + V + W);
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const float minUVW = min(U, min(V, W));
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const float maxUVW = max(U, max(V, W));
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/* Note the extended epsilon compared to ray_triangle_intersect, to account
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* for intersections with neighboring triangles that have an epsilon. */
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return (minUVW >= eps || maxUVW <= -eps);
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}
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/* Tests for an intersection between a ray and a quad defined by
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* its midpoint, normal and sides.
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* If ellipse is true, hits outside the ellipse that's enclosed by the
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* quad are rejected.
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*/
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ccl_device bool ray_quad_intersect(float3 ray_P,
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float3 ray_D,
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float ray_tmin,
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float ray_tmax,
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float3 quad_P,
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float3 quad_u,
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float3 quad_v,
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float3 quad_n,
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ccl_private float3 *isect_P,
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ccl_private float *isect_t,
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ccl_private float *isect_u,
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ccl_private float *isect_v,
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bool ellipse)
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{
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/* Perform intersection test. */
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float t = -(dot(ray_P, quad_n) - dot(quad_P, quad_n)) / dot(ray_D, quad_n);
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if (!(t > ray_tmin && t < ray_tmax)) {
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return false;
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}
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const float3 hit = ray_P + t * ray_D;
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const float3 inplane = hit - quad_P;
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const float u = dot(inplane, quad_u) / dot(quad_u, quad_u);
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if (u < -0.5f || u > 0.5f) {
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return false;
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}
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const float v = dot(inplane, quad_v) / dot(quad_v, quad_v);
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if (v < -0.5f || v > 0.5f) {
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return false;
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}
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if (ellipse && (u * u + v * v > 0.25f)) {
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return false;
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}
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/* Store the result. */
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/* TODO(sergey): Check whether we can avoid some checks here. */
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if (isect_P != NULL)
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*isect_P = hit;
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if (isect_t != NULL)
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*isect_t = t;
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/* NOTE: Return barycentric coordinates in the same notation as Embree and OptiX. */
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if (isect_u != NULL)
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*isect_u = v + 0.5f;
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if (isect_v != NULL)
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*isect_v = -u - v;
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return true;
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}
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CCL_NAMESPACE_END
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#endif /* __UTIL_MATH_INTERSECT_H__ */
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