Ray tracer not giving different light intensities based on direction - c

Question

Goal: I am trying to create a ray tracer in C. I just added in a light source that should give each of my three spheres a shading effect based on where the light is. If the light is to the left of all of them, a shadow should be cased on the right.
Problem: When changing the light intensities and position of the light, all the spheres are changed uniformly. The spheres will be more or less lit equally and there is no variation of lighting on individual pixels on the sphere.
My debugging attempts: I have tried looking through the variable outputs by printing out a lot of different info and I think the source comes from my variable
diffuse_light_intensity
which does not change much (through all the iterations on the screen the value changes twice when it should be changing quite often due to the angles of the light on the surface changing quite a bit)
My Code: (my theory is the problem lies in scene_intersect() or cast_ray())
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <math.h>
#include <limits.h>
typedef struct {
float position[3];
float intensity;
} Light;
typedef struct {
float diffuse_color[3];
} Material;
typedef struct {
float center[3];
float radius;
Material material;
} Sphere;
int arrSub(const float arr1[], const float arr2[], float subArr[], int length) {
/*
Requires 3 equally sized arrays (denoted as length),
arr1 - arr2 will result in the third array subArr
*/
for (int i = 0; i < length; i++) {
subArr[i] = arr1[i] - arr2[i];
}
return 0;
}
int arrAdd(const float arr1[], const float arr2[], float addArr[], int length) {
/*
Requires 3 equally sized arrays (denoted as length),
arr1 + arr2 will result in the third array subArr
*/
for (int i = 0; i < length; i++) {
addArr[i] = arr1[i] + arr2[i];
}
return 0;
}
int arrScalarMult(const float arr1[], float scalar, float newArr[], int length) {
/*
Requires 3 equally sized arrays (denoted as length),
arr1 - arr2 will result in the third array subArr
*/
for (int i = 0; i < length; i++) {
newArr[i] = arr1[i] * scalar;
}
return 0;
}
float dotProduct(const float arr1[], const float arr2[], int length) {
/*
Returns the dot product of two equal sized arrays
(treated as vectors)
a (dot) b = a1b1 + a2b2 + ... anbn
*/
float result = 0;
for (int i = 0; i < length; i++) {
result += arr1[i] * arr2[i];
}
return result;
}
int normalize(float arr[], int len) {
//Normalize a vector (array)
float sumSqr;
float norm;
for (int i = 0; i < len; i++) {
sumSqr += arr[i] * arr[i];
}
norm = sqrt(sumSqr);
for (int i = 0; i < len; i++) {
arr[i] = arr[i] / norm;
}
return 0;
}
bool ray_intersect(const float origin[], const float dir[], float t0, Sphere s) {
/*
Ray-Sphere Intersection
Vectors:
origin (the zero vector)
dir (direction vector)
L (vector from origin to center of sphere)
Scalars:
tca
d2
thc
t0
t1
*/
float L[3] = {0,0,0}; //The zero vector
arrSub(s.center, origin, L, 3); //L is now the vector from origin to the sphere's center
float tca = dotProduct(L, dir, 3); //Projection of L onto dir
float d2 = dotProduct(L, L, 3) - tca*tca;
if (d2 > s.radius * s.radius) return false; //There is no intersection, so return false.
float thc = sqrtf((s.radius*s.radius - d2));
t0 = tca - thc;
float t1 = tca + thc;
if (t0 < 0) {
t0 = t1;
}
if (t0 < 0) return false;
return true;
}
bool scene_intersect(const float origin[], const float dir[], const Sphere s[], int len, float hit[], float N[], Material * ptr_m) {
float sphere_dist = INT_MAX;
for (size_t i=0; i < len; i++) {
float dist_i;
if (ray_intersect(origin, dir, dist_i, s[i]) && dist_i < sphere_dist) {
sphere_dist = dist_i;
float dirDist[3];
arrScalarMult(dir, dist_i, dirDist, 3);
arrAdd(origin, dirDist, hit, 3);
float hitMinusCenter[3];
arrSub(hit, s[i].center, hitMinusCenter, 3);
normalize(hitMinusCenter, 3);
N[0] = hitMinusCenter[0];
N[1] = hitMinusCenter[1];
N[2] = hitMinusCenter[2];
* ptr_m = s[i].material;
}
}
return sphere_dist<1000;
}
int cast_ray(const float origin[], const float dir[], const Sphere s[], const Light l[], int l_size, unsigned char colorArr[]) {
float point[3], N[3];
Material m;
Material * ptr_m = &m;
if (!scene_intersect(origin, dir, s, 3, point, N, ptr_m)) {
//background
colorArr[0] = 5; //red
colorArr[1] = 100; //green
colorArr[2] = 250; //blue
} else {
float diffuse_light_intensity = 0;
float light_dir[3];
for (size_t i = 0; i < l_size; i++) {
arrSub(l[i].position, point, light_dir, 3);
normalize(light_dir, 3);
diffuse_light_intensity += l[i].intensity * ((0.f >= dotProduct(light_dir, N, 3) ? (0.f) : (dotProduct(light_dir, N, 3))));
}
//light up pixel
colorArr[0] = m.diffuse_color[0] * diffuse_light_intensity;
colorArr[1] = m.diffuse_color[1] * diffuse_light_intensity;
colorArr[2] = m.diffuse_color[2] * diffuse_light_intensity;
}
return 0;
}
int render(const Sphere s[], const Light l[], int l_length) {
/*
Creates image in a new color each step.
*/
const int width = 1024;
const int height = 768;
FILE *fp = fopen("fourth.ppm", "wb"); // Write in binary mode
(void) fprintf(fp, "P6\n%d %d\n255\n", width, height);
float fov = 3.1415926535/2.; // Field of View
#pragma omp parallel for
for (size_t j = 0; j < height; j++) {
for (size_t i = 0; i < width; i++) {
float x = (2*(i+.5)/(float)width - 1)*tan(fov/2.)*width/(float)height;
float y = -(2*(j+.5)/(float)height - 1)*tan(fov/2.);
float dir[] = {x,y,-1};
normalize(dir, 3);
unsigned char color[3];
const float origin[] = {0,0,0};
cast_ray(origin, dir, s, l, l_length, color);
(void) fwrite(color, 1, 3, fp);
}
}
(void) fclose(fp);
return 0;
}
int main(void) {
Material red = {255,0,0};
Material pink = {150,10,150};
Material gold = {255, 195, 0};
//Populate with spheres
Sphere s[3];
Sphere originalS = {{-3,0,-16},2,gold};
Sphere bigS = {{-1.0, -1.5, -12}, 3, red};
Sphere anotherS = {{7,5,-18},2,pink};
s[0] = originalS;
s[1] = bigS;
s[2] = anotherS;
//Add light source
Light l[1];
Light test_light = {{-20,20,20}, 1.5};
l[0] = test_light;
render(s,l, 1);
printf("Run success!\n");
return 0;
}
If any clarification is needed on my code please let me know, I am quite new to both C and stackoverflow.

Answer 1

There's a fundamental error in ray_intersect where you're passing the t0 variable by value, and not as a pointer, and therefore in the scene_intersect function its value is always zero.
The other problem is that you don't initialize the sumSqr in the normalize function, resulting in that function returning NaN for each vector component.
With those two fixed I get something approximating shaded balls. The errors in that image are caused by failing to ensure that your output pixel values fall in the range [0, 255].
NB: both of these first errors are detected if you turn on full compiler error checking, warning you of uninitialised variables being used.