From 6c88e0028c11721499ef93a6df651df3a41150c3 Mon Sep 17 00:00:00 2001
From: Tavian Barnes <tavianator@gmail.com>
Date: Sun, 14 Jun 2009 19:58:12 +0000
Subject: Use z-index coloring for ray-tracing.

---
 libdimension/raytrace.c | 28 +++++++++++++++++++---------
 tests/raytrace.c        |  7 ++++++-
 2 files changed, 25 insertions(+), 10 deletions(-)

diff --git a/libdimension/raytrace.c b/libdimension/raytrace.c
index 316157a..e91dbb2 100644
--- a/libdimension/raytrace.c
+++ b/libdimension/raytrace.c
@@ -66,12 +66,15 @@ dmnsn_raytrace_scene(dmnsn_scene *scene)
 static void *
 dmnsn_raytrace_scene_thread(void *arg)
 {
-  unsigned int i, j, k;
+  unsigned int i, j, k, l;
+  double t, t_temp;
   dmnsn_object *object;
   dmnsn_line ray, ray_trans;
   dmnsn_raytrace_thread_payload *payload = (dmnsn_raytrace_thread_payload *)arg;
   dmnsn_scene *scene = payload->scene;
   dmnsn_array *intersections;
+  dmnsn_color color;
+  dmnsn_sRGB sRGB;
 
   /* Iterate through each pixel */
   for (i = 0; i < scene->canvas->x; ++i) {
@@ -79,7 +82,8 @@ dmnsn_raytrace_scene_thread(void *arg)
       /* Only do the pixels assigned to this thread */
       if ((j*scene->canvas->x + i)%payload->n == payload->i) {
         /* Set the pixel to the background color */
-        dmnsn_set_pixel(scene->canvas, i, j, scene->background);
+        color = scene->background;
+        t = 0.0;
 
         /* Get the ray corresponding to the (i,j)th pixel */
         ray = (*scene->camera->ray_fn)(scene->camera, scene->canvas, i, j);
@@ -90,17 +94,23 @@ dmnsn_raytrace_scene_thread(void *arg)
           /* Transform the ray according to the object */
           ray_trans = dmnsn_matrix_line_mul(object->trans, ray);
 
-          /* Test for an intersection with an object */
+          /* Test for intersections with objects */
           intersections = (*object->intersections_fn)(object, ray_trans);
-          if (intersections->length > 0) {
-            /* Mark intersections white */
-            dmnsn_set_pixel(scene->canvas, i, j,
-                            dmnsn_color_from_XYZ(dmnsn_whitepoint));
-            dmnsn_delete_array(intersections);
-            break;
+          for (l = 0; l < intersections->length; ++l) {
+            dmnsn_array_get(intersections, l, &t_temp);
+            if (t_temp < t || t == 0.0) t = t_temp;
           }
           dmnsn_delete_array(intersections);
         }
+
+        if (t != 0.0) {
+          sRGB.R = 1.0 - (t - 2.25)/2.25;
+          sRGB.G = sRGB.R;
+          sRGB.B = sRGB.R;
+          color = dmnsn_color_from_sRGB(sRGB);
+        }
+
+        dmnsn_set_pixel(scene->canvas, i, j, color);
       }
     }
   }
diff --git a/tests/raytrace.c b/tests/raytrace.c
index ec13782..c8c25cd 100644
--- a/tests/raytrace.c
+++ b/tests/raytrace.c
@@ -25,7 +25,7 @@
 int main() {
   FILE *file;
   dmnsn_scene *scene;
-  dmnsn_object *cube;
+  dmnsn_object *sphere, *cube;
   dmnsn_sRGB sRGB;
   dmnsn_color color;
   dmnsn_matrix trans;
@@ -58,6 +58,10 @@ int main() {
   color.filter = 0.1;
   scene->background = color;
 
+  sphere = dmnsn_new_sphere();
+  sphere->trans = dmnsn_scale_matrix(dmnsn_vector_construct(0.8, 0.8, 0.8));
+  dmnsn_array_push(scene->objects, &sphere);
+
   cube = dmnsn_new_cube();
   cube->trans = dmnsn_rotation_matrix(dmnsn_vector_construct(0.75, 0.0, 0.0));
   dmnsn_array_push(scene->objects, &cube);
@@ -68,6 +72,7 @@ int main() {
   dmnsn_png_write_canvas(scene->canvas, file);
 
   dmnsn_delete_cube(cube);
+  dmnsn_delete_sphere(sphere);
   dmnsn_delete_perspective_camera(scene->camera);
   dmnsn_delete_canvas(scene->canvas);
   dmnsn_delete_scene(scene);
-- 
cgit v1.2.3