Move camera initialisation into seperate module

src/camera.c

@@ -0,0 +1,26 @@
+#include "camera.h"
+
+camera_t camera_init(
+    vec3_t pos, double focal_len, double viewport_height, uint32_t img_width,
+    uint32_t img_height)
+{
+	const double aspect = (double)img_width / (double)img_height;
+	const double viewport_width = viewport_height * aspect;
+	const vec3_t viewport_disp = { 0, 0, focal_len };
+	const vec3_t u = { viewport_width, 0, 0 };
+	const vec3_t v = { 0, -viewport_height, 0 };
+	const vec3_t topleft = vec3_sub(
+	    vec3_sub(pos, viewport_disp), vec3_scale(vec3_add(u, v), 0.5));
+
+	const vec3_t x_step = vec3_scale(u, 1.0 / (double)img_width);
+	const vec3_t y_step = vec3_scale(v, 1.0 / (double)img_height);
+	const vec3_t pix_origin
+	    = vec3_add(topleft, vec3_scale(vec3_add(x_step, y_step), 0.5));
+
+	return (camera_t) {
+		.pos = pos,
+		.pix_origin = pix_origin,
+		.x_step = x_step,
+		.y_step = y_step,
+	};
+}