Create initial raytraced scene

src/raytracer/main.c

@@ -1,22 +1,77 @@
 #include "SDL_events.h"
 #include "c_cpp_aliases/aliases.h"
+#include "vector/vec.h"
 #include "window/window.h"
+#include <math.h>
 #include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>
 
+#define ARR_LEN(ARR) sizeof(ARR) / sizeof(ARR[0])
+
+typedef struct {
+  f32 radius;
+  vec3f_t centre;
+  colour_t colour;
+} sphere_t;
+
+typedef struct {
+  sphere_t *spheres;
+  u32 count;
+} scene_t;
+
+typedef struct {
+  f32 t1;
+  f32 t2;
+} solutions_t;
+
+solutions_t ray_intersects_sphere(vec3f_t origin, vec3f_t direction,
+                                  sphere_t sphere);
+colour_t trace_ray(vec3f_t origin, vec3f_t direction, f32 t_min, f32 t_max,
+                   const scene_t *scene, colour_t default_colour);
+
 int main(int argc, char *argv[]) {
   colour_t bg = (colour_t){.r = 128, .g = 128, .b = 128, .a = 255};
+  vec3f_t camera = {.x = 0.0f, .y = 0.0f, .z = 0.0f};
+  vec3f_t viewport = {.x = 1.0f, .y = 1.0f, .z = 1.0f};
 
   window_t window = {0};
 
-  if (!init_window(&window, 1000, 800, "CG From Scratch")) {
+  if (!init_window(&window, 800, 800, "CG From Scratch")) {
     return EXIT_FAILURE;
   }
 
   bool running = true;
   SDL_Event event = {0};
 
+  sphere_t spheres[] = {
+      (sphere_t){
+          .radius = 1.0f,
+          .centre = (vec3f_t){.x = 0.0f, .y = -1.0f, .z = 3.0f},
+          .colour = (colour_t){.r = 255, .g = 0, .b = 0, .a = 255},
+      },
+      (sphere_t){
+          .radius = 1.0f,
+          .centre = (vec3f_t){.x = -2.0f, .y = 0.0f, .z = 4.0f},
+          .colour = (colour_t){.r = 0, .g = 255, .b = 0, .a = 255},
+      },
+      (sphere_t){
+          .radius = 1.0f,
+          .centre = (vec3f_t){.x = 2.0f, .y = 0.0f, .z = 4.0f},
+          .colour = (colour_t){.r = 0, .g = 0, .b = 255, .a = 255},
+      },
+  };
+
+  scene_t scene = {
+      .spheres = spheres,
+      .count = ARR_LEN(spheres),
+  };
+
+  i32 w_min = ((i32)window.half_width) * -1;
+  i32 w_max = (i32)window.half_width;
+  i32 h_min = ((i32)window.half_height) * -1;
+  i32 h_max = (i32)window.half_height;
+
   while (running) {
     while (SDL_PollEvent(&event)) {
       switch (event.type) {
@@ -28,6 +83,14 @@ int main(int argc, char *argv[]) {
 
     clear_window(&window, bg);
 
+    for (i32 y = h_min; y < h_max; ++y) {
+      for (i32 x = w_min; x < w_max; ++x) {
+        vec3f_t direction = window_to_viewport(&window, x, y, viewport);
+        colour_t colour = trace_ray(camera, direction, 1, INFINITY, &scene, bg);
+        set_pixel(&window, x, y, colour);
+      }
+    }
+
     swap_buffers(&window);
   }
 
@@ -35,3 +98,52 @@ int main(int argc, char *argv[]) {
 
   return EXIT_SUCCESS;
 }
+
+solutions_t ray_intersects_sphere(vec3f_t origin, vec3f_t direction,
+                                  sphere_t sphere) {
+  f32 r = sphere.radius;
+  vec3f_t CO = vec_sub(vec3f_t, origin, sphere.centre);
+
+  f32 a = vec_dot(vec3f_t, direction, direction);
+  f32 b = 2.0f * vec_dot(vec3f_t, CO, direction);
+  f32 c = vec_dot(vec3f_t, CO, CO) - r * r;
+
+  f32 discriminant = b * b - 4 * a * c;
+  if (discriminant < 0) {
+    return (solutions_t){INFINITY, INFINITY};
+  }
+
+  f32 t1 = (-b + sqrtf(discriminant)) / (2 * a);
+  f32 t2 = (-b - sqrtf(discriminant)) / (2 * a);
+
+  return (solutions_t){t1, t2};
+}
+
+colour_t trace_ray(vec3f_t origin, vec3f_t direction, f32 t_min, f32 t_max,
+                   const scene_t *scene, colour_t default_colour) {
+  f32 closest_t = INFINITY;
+  sphere_t *closest_sphere = NULL;
+
+  for (u32 i = 0; i < scene->count; ++i) {
+    solutions_t solutions =
+        ray_intersects_sphere(origin, direction, scene->spheres[i]);
+
+    if (solutions.t1 >= t_min && solutions.t1 <= t_max &&
+        solutions.t1 < closest_t) {
+      closest_t = solutions.t1;
+      closest_sphere = &(scene->spheres[i]);
+    }
+
+    if (solutions.t2 >= t_min && solutions.t2 <= t_max &&
+        solutions.t2 < closest_t) {
+      closest_t = solutions.t2;
+      closest_sphere = &(scene->spheres[i]);
+    }
+  }
+
+  if (!closest_sphere) {
+    return default_colour;
+  }
+
+  return closest_sphere->colour;
+}