130 lines
5.1 KiB
Metal
130 lines
5.1 KiB
Metal
//
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/**
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* Copyright (c) 2018 Razeware LLC
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* Notwithstanding the foregoing, you may not use, copy, modify, merge, publish,
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* distribute, sublicense, create a derivative work, and/or sell copies of the
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* Software in any work that is designed, intended, or marketed for pedagogical or
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* instructional purposes related to programming, coding, application development,
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* or information technology. Permission for such use, copying, modification,
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* merger, publication, distribution, sublicensing, creation of derivative works,
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* or sale is expressly withheld.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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#include <metal_stdlib>
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#include <simd/simd.h>
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#import "ShaderTypes.h"
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using namespace metal;
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// Add structs here
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/*
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// Interpolates vertex attribute of an arbitrary type across the surface of a triangle
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// given the barycentric coordinates and triangle index in an intersection struct
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template<typename T>
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inline T interpolateVertexAttribute(device T *attributes, Intersection intersection) {
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float3 uvw;
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uvw.xy = intersection.coordinates;
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uvw.z = 1.0 - uvw.x - uvw.y;
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unsigned int triangleIndex = intersection.primitiveIndex;
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T T0 = attributes[triangleIndex * 3 + 0];
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T T1 = attributes[triangleIndex * 3 + 1];
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T T2 = attributes[triangleIndex * 3 + 2];
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return uvw.x * T0 + uvw.y * T1 + uvw.z * T2;
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}
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*/
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// Uses the inversion method to map two uniformly random numbers to a three dimensional
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// unit hemisphere where the probability of a given sample is proportional to the cosine
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// of the angle between the sample direction and the "up" direction (0, 1, 0)
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inline float3 sampleCosineWeightedHemisphere(float2 u) {
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float phi = 2.0f * M_PI_F * u.x;
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float cos_phi;
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float sin_phi = sincos(phi, cos_phi);
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float cos_theta = sqrt(u.y);
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float sin_theta = sqrt(1.0f - cos_theta * cos_theta);
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return float3(sin_theta * cos_phi, cos_theta, sin_theta * sin_phi);
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}
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// Maps two uniformly random numbers to the surface of a two-dimensional area light
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// source and returns the direction to this point, the amount of light which travels
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// between the intersection point and the sample point on the light source, as well
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// as the distance between these two points.
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inline void sampleAreaLight(constant AreaLight & light,
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float2 u,
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float3 position,
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thread float3 & lightDirection,
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thread float3 & lightColor,
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thread float & lightDistance)
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{
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// Map to -1..1
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u = u * 2.0f - 1.0f;
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// Transform into light's coordinate system
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float3 samplePosition = light.position +
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light.right * u.x +
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light.up * u.y;
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// Compute vector from sample point on light source to intersection point
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lightDirection = samplePosition - position;
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lightDistance = length(lightDirection);
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float inverseLightDistance = 1.0f / max(lightDistance, 1e-3f);
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// Normalize the light direction
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lightDirection *= inverseLightDistance;
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// Start with the light's color
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lightColor = light.color;
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// Light falls off with the inverse square of the distance to the intersection point
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lightColor *= (inverseLightDistance * inverseLightDistance);
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// Light also falls off with the cosine of angle between the intersection point and
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// the light source
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lightColor *= saturate(dot(-lightDirection, light.forward));
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}
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// Aligns a direction on the unit hemisphere such that the hemisphere's "up" direction
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// (0, 1, 0) maps to the given surface normal direction
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inline float3 alignHemisphereWithNormal(float3 sample, float3 normal) {
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// Set the "up" vector to the normal
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float3 up = normal;
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// Find an arbitrary direction perpendicular to the normal. This will become the
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// "right" vector.
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float3 right = normalize(cross(normal, float3(0.0072f, 1.0f, 0.0034f)));
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// Find a third vector perpendicular to the previous two. This will be the
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// "forward" vector.
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float3 forward = cross(right, up);
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// Map the direction on the unit hemisphere to the coordinate system aligned
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// with the normal.
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return sample.x * right + sample.y * up + sample.z * forward;
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}
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