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harieamjari/sphere.c

Last active Dec 25, 2020
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Minimal ray sphere intersection in C
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <png.h>
#include <assert.h>
struct vec3D {
double x,y,z;
};
int width, height;
static double dot_product(const struct vec3D a, const struct vec3D b){
return a.x*b.x+a.y*b.y+a.z*b.z;
}
static double magnitude(const struct vec3D a){
return sqrt(dot_product(a,a));
}
int main(int argc, char *argv[]){
double Pz, c, r;
if (argc != 4) {
printf("usage: %s Pz c r\n\n"
"Pz = image plane z location\n"
"c = sphere z center\n"
"r = sphere radius\nusing default: Pz = 40, c = 202, r = 200\n" , argv[0]);
Pz = 40.0; c = 202.0; r = 200.0;
} else {Pz = atof(argv[1]), c = atof(argv[2]), r = atof(argv[3]);}
width = 1000, height = 1000;
FILE *fp = fopen("t.png", "wb");
assert(fp!=NULL);
png_structp png = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
assert(png);
png_infop info = png_create_info_struct(png);
assert(info);
int tem = setjmp(png_jmpbuf(png));
assert(!tem);
png_init_io(png, fp);
png_set_IHDR(
png,
info,
width, height,
8,
PNG_COLOR_TYPE_RGBA,
PNG_INTERLACE_NONE,
PNG_COMPRESSION_TYPE_DEFAULT,
PNG_FILTER_TYPE_DEFAULT);
png_write_info(png, info);
png_bytep *row = NULL;
row = malloc(sizeof(png_bytep)*height);
assert(row!=NULL);
for (int y = 0; y < height; y++){
row[y] = malloc(sizeof(png_bytep)*width);
assert(row[y]!=NULL);
}
struct vec3D light_source = {.x=-0.95,.y=0.0,.z=-0.31224}; /* magnitude = 1 */
for (int y = 0; y < height; y++){
png_bytep line = row[y];
for (int x = 0; x < width; x++){
double Px = x-(width/2), Py = (height/2)-y;
struct vec3D ray = {Px,Py,Pz};
double _magnitude = magnitude(ray);
struct vec3D normalized_ray = {ray.x/_magnitude, ray.y/_magnitude, ray.z/_magnitude};
struct vec3D sphere_center = {0.0,0.0,c};
double sphere_radius = r;
double v = dot_product(sphere_center, normalized_ray);
double delta = sphere_radius*sphere_radius-((dot_product(sphere_center,sphere_center)-v*v));
if (delta>0.0||delta==0.0){
double d = sqrt(delta);
struct vec3D intersection = {(v-d)*normalized_ray.x, (v-d)*normalized_ray.y, (v-d)*normalized_ray.z};
/* center the temp_normal at origin */
struct vec3D temp_normal = intersection;
temp_normal.x -= sphere_center.x; temp_normal.y -= sphere_center.y;
temp_normal.z -= sphere_center.z;
/* normalized temp_normal */
struct vec3D normal = {temp_normal.x/magnitude(temp_normal),
temp_normal.y/magnitude(temp_normal),
temp_normal.z/magnitude(temp_normal)};
double _dot_product = dot_product(normal, light_source);
if (_dot_product<0) _dot_product = 0.0;
*(line+(x*4)+0)=(unsigned char)(_dot_product*255.0);
*(line+(x*4)+1)=(unsigned char)(_dot_product*255.0);
*(line+(x*4)+2)=(unsigned char)(_dot_product*255.0);
*(line+(x*4)+3)=0xFF;
}
else if (delta<0.0){/* no intersection. AKA an imagninary sphere */
*(line+(x*4)+0)=0x00;
*(line+(x*4)+1)=0x00;
*(line+(x*4)+2)=0x00;
*(line+(x*4)+3)=0xFF;}
}
}
png_write_image(png, row);
png_write_end(png, NULL);
for (int y = 0; y < height; y++) free(row[y]);
free(row);
fclose(fp);
png_destroy_write_struct(&png, &info);
return 0;
}
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@harieamjari harieamjari commented Dec 24, 2020

t

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