openCl path tracer creates strange noise patterns - c++

Question

I've made a path tracer using openCl and c++, following the basic structure in this tutorial: http://raytracey.blogspot.com/2016/11/opencl-path-tracing-tutorial-2-path.html. As far as I can tell, nothing is wrong with the path tracing algorithm itself, but I get strange stripe patterns in the image that don't match the regular noise of path tracing. striped image
There are distinct vertical stripes and more narrow horizontal ones that make the image look granular regardless of how many samples I take per pixel. Again, pixel by pixel, the path tracer seems to be working (the outlines of objects are correct even where they appear mid-stripe) as seen here: close-up.
The only difference between my code and the one in the tutorial I link is that Sam Lapere appears to be using the c++ wrapper for openCl, and I've added a couple of features like movement. There also are a few differences in how I'm handling light bounces.
I'm new to openCl. What could be causing this? It seems like it doesn't have to do with my ray tracer itself, but somehow in the way I'm implementing openCl. I'm also using an SDL texture and renderer to show the image to the screen
here is the tracer code if it helps:
kernel:
__kernel void render_kernel
(__constant struct Sphere* spheres, const int width, const int height,
const int sphere_count, __global int * output, __global float3*
pixel_buckets, __global int* counter, __constant struct Ray* camera,
__global bool* reset){
int gid = get_global_id(0);
//for movement
if (*reset){
pixel_buckets[gid] = (float3)(0,0,0);
counter[gid] = 0;
}
int xcoord = gid % width;
int ycoord = gid / width;
struct Ray camray = createCamRay(xcoord, ycoord, width, height, counter[gid], camera);
float3 final_color = trace(spheres, &camray, sphere_count, xcoord, ycoord);
counter[gid] ++;
//average colors
pixel_buckets[gid] += final_color;
output[gid] = colorInt(clampColor(pixel_buckets[gid] / counter[gid]));
}
trace:
float3 trace(__constant struct Sphere* spheres, struct Ray* camray, const int sphere_count,
unsigned int seed0, unsigned int seed1){
struct Ray ray = *camray;
struct Sphere sphere1;
sphere1.center = (float3)(0, 0, 3);
sphere1.radius = 0.7;
sphere1.color = (float3)(1,1,0);
const int bounce_count = 8;
float3 colors[20];
float3 emiss[20];
for (int bounce = 0; bounce < bounce_count; bounce ++){
int sphere_id = 0;
float hit_distance = intersectScene(spheres, &ray, &sphere_id, sphere_count);
struct Sphere hit_sphere = spheres[sphere_id];
float3 hit_point = ray.origin + (ray.direction * hit_distance);
float3 normal = normalize(hit_point - hit_sphere.center);
if (dot(normal, -ray.direction) < 0){
normal = -normal;
}
//random bounce angles
float rand_theta = get_random(seed0, seed1);
float theta = acos(sqrt(rand_theta));
float rand_phi = get_random(seed0, seed1);
float phi = 2 * PI * rand_phi;
//scales the tnb vectors
float x = sin(theta) * sin(phi);
float y = sin(theta) * cos(phi);
float n = cos(theta);
float3 hemx = normalize(cross(ray.direction, normal)) * x;
float3 hemy = normalize(cross(hemx, normal)) * y;
normal = normal * n;
float3 new_ray = normalize(hemx + hemy + normal);
ray.origin = hit_point + (normal * EPSILON);
ray.direction = new_ray;
colors[bounce] = hit_sphere.color;
emiss[bounce] = hit_sphere.emmissive;
}
colors[bounce_count] = (float3)(0,0,0);
emiss[bounce_count] = (float3)(0,0,0);
for (int i = bounce_count - 1; i >= 0; i--){
colors[i] = (colors[i] * emiss[i]) + (colors[i] * colors[i + 1]);
}
return colors[0];
}
random number generator:
float get_random(unsigned int *seed0, unsigned int *seed1) {
/* hash the seeds using bitwise AND operations and bitshifts */
*seed0 = 36969 * ((*seed0) & 65535) + ((*seed0) >> 16);
*seed1 = 18000 * ((*seed1) & 65535) + ((*seed1) >> 16);
unsigned int ires = ((*seed0) << 16) + (*seed1);
/* use union struct to convert int to float */
union {
float f;
unsigned int ui;
} res;
res.ui = (ires & 0x007fffff) | 0x40000000; /* bitwise AND, bitwise OR */
return (res.f - 2.0f) / 2.0f;
}
thanks