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gpu.frag
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gpu.frag
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#version 430
#define SAMPLES_PER_PIXEL 256 // should prob be a uniform
#define MAX_DEPTH 50 // this too
#define MAX_MODELS 10
struct VoxelModel {
vec3 position;
ivec3 size;
};
uniform uvec2 iResolution;
uniform int numModels;
uniform VoxelModel models[MAX_MODELS];
layout(std430, binding = 0) buffer ssbo { // model data
vec4 data[];
};
out vec4 fragColor;
struct Ray {
vec3 origin;
vec3 direction;
};
struct HitRecord {
vec3 p;
float t;
vec3 normal;
vec3 albedo; // should be replaced by material
};
// PCG random number generation, [0, 1] inclusive
// https://nvpro-samples.github.io/vk_mini_path_tracer/index.html#antialiasingandpseudorandomnumbergeneration/pseudorandomnumbergenerationinglsl
uint rngState = iResolution.x * uint(gl_FragCoord.y) + uint(gl_FragCoord.x);
uint stepRandom(uint rngState) { return rngState * 747796405 + 1; }
float random(inout uint rngState) {
rngState = stepRandom(rngState);
uint word = ((rngState >> ((rngState >> 28) + 4)) ^ rngState) * 277803737;
word = (word >> 22) ^ word;
return float(word) / 4294967295.0f;
}
bool voxelPresent(ivec3 voxOrigin, out vec3 albedo) {
ivec3 modelSize = models[0].size;
if (voxOrigin.x >= modelSize.x || voxOrigin.y >= modelSize.y || voxOrigin.z >= modelSize.z || voxOrigin.x < 0 || voxOrigin.y < 0 || voxOrigin.z < 0) {
return false;
}
vec4 voxel = data[voxOrigin.x + voxOrigin.y * modelSize.x + voxOrigin.z * modelSize.x * modelSize.y];
albedo = voxel.xyz;
return voxel.a > 0;
}
bool voxelMarch(Ray ray, out HitRecord rec) {
ivec3 voxOrigin = ivec3(floor(ray.origin));
ivec3 posStepDir = ivec3(step(0.0, ray.direction)); // 0.0 <= rayDirection ? 1.0 : 0.0
ivec3 stepDir = ivec3(posStepDir * 2 - 1);
ivec3 justOut = ivec3(posStepDir * (models[0].size - 1) + stepDir);
vec3 tMax = (posStepDir - (ray.origin - voxOrigin)) / ray.direction;
vec3 tDelta = stepDir / ray.direction;
ivec3 lastOrigin = voxOrigin;
float tMin = 0;
for (int i = 0; i < 1000; ++i) {
bool present = voxelPresent(voxOrigin, rec.albedo);
if (present) {
rec.normal = lastOrigin - voxOrigin;
rec.t = tMin;
rec.p = ray.origin + tMin * ray.direction;
return true;
}
lastOrigin = voxOrigin;
if (tMax.x < tMax.y) {
if (tMax.x < tMax.z) {
voxOrigin.x += stepDir.x;
if (voxOrigin.x == justOut.x) { break; }
tMin = tMax.x;
tMax.x += tDelta.x;
} else {
voxOrigin.z += stepDir.z;
if (voxOrigin.z == justOut.z) { break; }
tMin = tMax.z;
tMax.z += tDelta.z;
}
} else {
if (tMax.y < tMax.z) {
voxOrigin.y += stepDir.y;
if (voxOrigin.y == justOut.y) { break; }
tMin = tMax.y;
tMax.y += tDelta.y;
} else {
voxOrigin.z += stepDir.z;
if (voxOrigin.z == justOut.z) { break; }
tMin = tMax.z;
tMax.z += tDelta.z;
}
}
}
return false;
}
bool groundHit(Ray ray, out HitRecord rec) {
float t = (0 - ray.origin.y) / ray.direction.y; // replace 0 with y position of ground, TODO make configurable
if (t < 0 || t > 50) { // 100 for now, TODO use interval object
return false;
}
rec.normal = vec3(0.0, float(ray.direction.y < 0) * 2.0 - 1.0, 0.0);
rec.t = t;
rec.albedo = vec3(0.8, 0.8, 0.0);
rec.p = ray.origin + ray.direction * t;
return true;
}
// TODO improve this function lol
bool worldHit(Ray ray, out HitRecord rec) {
HitRecord ground_rec;
HitRecord vox_rec;
bool ground = groundHit(ray, ground_rec);
bool vox = voxelMarch(ray, vox_rec);
if (ground && vox) {
if (ground_rec.t < vox_rec.t) {
rec = ground_rec;
return true;
} else {
rec = vox_rec;
return true;
}
}
if (ground) {
rec = ground_rec;
return true;
}
if (vox) {
rec = vox_rec;
return true;
}
return false;
}
float randrange(float range_min, float range_max) {
return range_min + (range_max - range_min) * random(rngState);
}
vec3 random_in_unit_sphere() {
vec3 p = vec3(randrange(-1,1), randrange(-1,1), randrange(-1,1));
for (int i = 0; i < 20; i++) {
if (p.x * p.x + p.y * p.y + p.z * p.z < 1) {
return p;
}
}
return p;
}
vec3 random_unit_vector() {
return normalize(random_in_unit_sphere());
}
Ray get_ray() {
float image_width = iResolution.x;
float image_height = iResolution.y;
float aspect_ratio = image_width / image_height;
vec3 center = vec3(models[0].size.x / 2, models[0].size.y / 2, models[0].size.z + 12);
float focal_length = 1.0;
float viewport_height = 2.0;
float viewport_width = viewport_height * image_width / image_height;
vec3 viewport_u = vec3(viewport_width, 0.0, 0.0);
vec3 viewport_v = vec3(0.0, viewport_height, 0.0);
vec3 pixel_delta_u = viewport_u / image_width;
vec3 pixel_delta_v = viewport_v / image_height;
vec3 viewport_lower_left = center - vec3(0, 0, focal_length) - viewport_u / 2 - viewport_v / 2;
vec3 pixel00_loc = viewport_lower_left + 0.5 * (pixel_delta_u + pixel_delta_v);
return Ray(
center,
normalize((pixel00_loc + (gl_FragCoord.x - 0.5 + random(rngState)) * pixel_delta_u
+ (gl_FragCoord.y - 0.5 + random(rngState)) * pixel_delta_v) - center)
);
}
vec3 get_color() {
vec3 out_color = vec3(1, 1, 1);
Ray ray = get_ray();
HitRecord rec;
for (int d = 0; d < MAX_DEPTH; d++) {
if (worldHit(ray, rec)) {
vec3 scatter_dir = rec.normal + random_unit_vector();
// handle scatter_dir near zero case
if (scatter_dir.x < 1e-8 && scatter_dir.y < 1e-8 && scatter_dir.z < 1e-8) {
scatter_dir = rec.normal;
}
ray.origin = rec.p + scatter_dir * 0.001;
ray.direction = scatter_dir;
out_color *= rec.albedo;
} else {
float a = 0.5 * (ray.direction.y + 1.0);
out_color *= mix(vec3(1.0, 1.0, 1.0), vec3(0.5, 0.7, 1.0), a);
break;
}
}
return out_color;
}
void main() {
vec3 out_color = vec3(0, 0, 0);
for (int s = 0; s < SAMPLES_PER_PIXEL; s++) {
out_color += get_color();
}
fragColor = vec4(sqrt(out_color / SAMPLES_PER_PIXEL), 1.0);
}