Add background color

color.c

@@ -1,6 +1,14 @@
 #include "color.h"
 #include <stdio.h>
 
+color color_lerp(color c1, color c2, double t) {
+  return (color){
+      (1.0 - t) * c1.r + t * c2.r,
+      (1.0 - t) * c1.g + t * c2.g,
+      (1.0 - t) * c1.b + t * c2.b,
+  };
+}
+
 void color_write(FILE *out, color c) {
   fprintf(out, "%d %d %d\n", (int)(255.999 * c.r), (int)(255.999 * c.g),
           (int)(255.999 * c.b));

color.h

@@ -7,6 +7,8 @@ typedef struct color {
   double r, g, b;
 } color;
 
+color color_lerp(color c1, color c2, double t);
+
 void color_write(FILE *out, color c);
 
 #endif /* INCLUDED_COLOR_H */

main.c

@@ -1,21 +1,49 @@
 #include <stdio.h>
 
 #include "color.h"
+#include "point3.h"
+#include "ray.h"
+#include "vec3.h"
+
+color ray_color(ray r) {
+  vec3 unit_direction = vec3_normalize(r.direction);
+  double t = 0.5 * (unit_direction.y + 1.0);
+  color gradient1 = {1.0, 1.0, 1.0};
+  color gradient2 = {0.5, 0.7, 1.0};
+  return color_lerp(gradient1, gradient2, t);
+}
 
 int main(void) {
+  /* Image parameters */
+  const double aspect_ratio = 16.0 / 9.0;
   const int image_width = 256;
-  const int image_height = 256;
+  const int image_height = (int)(image_width / aspect_ratio);
+
+  /* Camera parameters */
+  double viewport_height = 2;
+  double viewport_width = aspect_ratio * viewport_height;
+  double focal_length = 1.0;
+
+  point3 origin = {0};
+  vec3 horizontal = {viewport_width, 0, 0};
+  vec3 vertical = {0, viewport_height, 0};
+  vec3 offset = vec3_add(vec3_div(horizontal, 2), vec3_div(vertical, 2));
+  offset = vec3_add(offset, (vec3){0, 0, focal_length});
+  point3 lower_left_corner = point3_add(origin, vec3_neg(offset));
 
   printf("P3\n%u %u\n255\n", image_width, image_height);
 
   for (int j = image_height - 1; j >= 0; --j) {
     fprintf(stderr, "\rScanlines remaining: %d      ", j);
     for (int i = 0; i < image_width; ++i) {
-      color pixel_color = {
-          .r = (double)(i) / (image_width - 1),
-          .g = (double)(j) / (image_height - 1),
-          .b = 0.25,
-      };
+      double u = (double)i / (image_width - 1);
+      double v = (double)j / (image_height - 1);
+      point3 screen_point =
+          point3_add(lower_left_corner,
+                     vec3_add(vec3_mul(u, horizontal), vec3_mul(v, vertical)));
+      vec3 direction = point3_sub(screen_point, origin);
+      ray r = {origin, direction};
+      color pixel_color = ray_color(r);
       color_write(stdout, pixel_color);
     }
   }
@@ -27,4 +55,5 @@ int main(void) {
 
 #include "color.c"
 #include "point3.c"
+#include "ray.c"
 #include "vec3.c"

ray.c

@@ -0,0 +1,6 @@
+#include "ray.h"
+#include "point3.h"
+
+point3 ray_at(ray r, double t) {
+  return point3_add(r.origin, vec3_mul(t, r.direction));
+}

ray.h

@@ -0,0 +1,14 @@
+#ifndef INCLUDED_RAY_H
+#define INCLUDED_RAY_H
+
+#include "point3.h"
+#include "vec3.h"
+
+typedef struct ray {
+  point3 origin;
+  vec3 direction;
+} ray;
+
+point3 ray_at(ray r, double t);
+
+#endif /* INCLUDED_RAY_H */