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ray_tracing_gltf: Match samplingHemisphere to Ray Tracing Gems implementation and avoid generating directions perpendicular to +z; adjust comments on Lambertian PDF and match docs.

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NeilBickford-NV 2023-05-23 14:45:28 -07:00
parent c436c46141
commit 80e00cae4e
3 changed files with 20 additions and 14 deletions
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18
ray_tracing_gltf/README.md
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@ -452,8 +452,8 @@ struct hitPayload
This modification will recursively trace until the `depth`hits 10 (hardcoded) or hit an emissive element (light).
The only information that we will keep from the shader, is the calculation of the hit state: position, normal. So
all code from `// Vector toward the light` to the end can be remove and be replaced by the following.
The only information that we will keep from the shader, is the calculation of the hit state: the position and normal. So
all code from `// Vector toward the light` to the end can be removed and be replaced by the following.
~~~~C
// https://en.wikipedia.org/wiki/Path_tracing
@ -467,12 +467,18 @@ all code from `// Vector toward the light` to the end can be remove and be repla
vec3 rayOrigin = world_position;
vec3 rayDirection = samplingHemisphere(prd.seed, tangent, bitangent, world_normal);
// Probability of the newRay (cosine distributed)
const float p = 1 / M_PI;
const float cos_theta = dot(rayDirection, world_normal);
// Probability density function of samplingHemisphere choosing this rayDirection
const float p = cos_theta / M_PI;
// Compute the BRDF for this ray (assuming Lambertian reflection)
float cos_theta = dot(rayDirection, world_normal);
vec3 BRDF = mat.pbrBaseColorFactor.xyz / M_PI;
vec3 albedo = mat.pbrBaseColorFactor.xyz;
if(mat.pbrBaseColorTexture > -1)
{
uint txtId = mat.pbrBaseColorTexture;
albedo *= texture(texturesMap[nonuniformEXT(txtId)], texcoord0).xyz;
}
vec3 BRDF = albedo / M_PI;
// Recursively trace reflected light sources.
if(prd.depth < 10)

7
ray_tracing_gltf/shaders/pathtrace.rchit
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@ -110,12 +110,11 @@ void main()
vec3 rayOrigin = world_position;
vec3 rayDirection = samplingHemisphere(prd.seed, tangent, bitangent, world_normal);
// Compute the BRDF for this ray (assuming Lambertian reflection)
float cos_theta = dot(rayDirection, world_normal);
// Probability of the newRay (cosine distributed)
const float cos_theta = dot(rayDirection, world_normal);
// Probability density function of samplingHemisphere choosing this rayDirection
const float p = cos_theta / M_PI;
// Compute the BRDF for this ray (assuming Lambertian reflection)
vec3 albedo = mat.pbrBaseColorFactor.xyz;
if(mat.pbrBaseColorTexture > -1)
{

9
ray_tracing_gltf/shaders/sampling.glsl
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@ -57,16 +57,17 @@ float rnd(inout uint prev)
// Sampling
//-------------------------------------------------------------------------------------------------
// Randomly sampling around +Z
// Randomly samples from a cosine-weighted hemisphere oriented in the `z` direction.
// From Ray Tracing Gems section 16.6.1, "Cosine-Weighted Hemisphere Oriented to the Z-Axis"
vec3 samplingHemisphere(inout uint seed, in vec3 x, in vec3 y, in vec3 z)
{
#define M_PI 3.141592
#define M_PI 3.14159265
float r1 = rnd(seed);
float r2 = rnd(seed);
float sq = sqrt(1.0 - r2);
float sq = sqrt(r1);
vec3 direction = vec3(cos(2 * M_PI * r1) * sq, sin(2 * M_PI * r1) * sq, sqrt(r2));
vec3 direction = vec3(cos(2 * M_PI * r2) * sq, sin(2 * M_PI * r2) * sq, sqrt(1. - r1));
direction = direction.x * x + direction.y * y + direction.z * z;
return direction;