From 4317faa8365b5c08d9111ddd1f0a622ed9e99b52 Mon Sep 17 00:00:00 2001
From: Tavian Barnes <tavianator@gmail.com>
Date: Wed, 7 Oct 2009 14:50:41 +0000
Subject: Add ray - bounding-box intersection test function.

---
 libdimension/raytrace.c | 72 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 72 insertions(+)

diff --git a/libdimension/raytrace.c b/libdimension/raytrace.c
index df61d6b..21ad1e8 100644
--- a/libdimension/raytrace.c
+++ b/libdimension/raytrace.c
@@ -229,6 +229,9 @@ dmnsn_raytrace_scene_impl(dmnsn_progress *progress, dmnsn_scene *scene,
   return 0;
 }
 
+static double dmnsn_ray_bounding_box(dmnsn_line ray,
+                                     dmnsn_vector min, dmnsn_vector max);
+
 /* Shoot a ray, and calculate the color, using `color' as the background */
 static dmnsn_color
 dmnsn_raytrace_shoot(dmnsn_scene *scene, dmnsn_color color, dmnsn_line ray)
@@ -286,3 +289,72 @@ dmnsn_raytrace_shoot(dmnsn_scene *scene, dmnsn_color color, dmnsn_line ray)
 
   return color;
 }
+
+static double
+dmnsn_ray_bounding_box(dmnsn_line ray, dmnsn_vector min, dmnsn_vector max)
+{
+  double t = -1.0, t_temp;
+  dmnsn_vector p;
+
+  if (line.n.x != 0.0) {
+    /* x == min.x */
+    t_temp = (min.x - line.x0.x)/line.n.x;
+    p = dmnsn_line_point(line, t_temp);
+    if (p.y >= min.y && p.y <= max.y && p.z >= min.z && p.z <= max.z
+        && t_temp >= 0.0 && (t < 0.0 || t_temp < t))
+    {
+      t = t_temp;
+    }
+
+    /* x == max.x */
+    t_temp = (max.x - line.x0.x)/line.n.x;
+    p = dmnsn_line_point(line, t_temp);
+    if (p.y >= min.y && p.y <= max.y && p.z >= min.z && p.z <= max.z
+        && t_temp >= 0.0 && (t < 0.0 || t_temp < t))
+    {
+      t = t_temp;
+    }
+  }
+
+  if (line.n.y != 0.0) {
+    /* y == -1.0 */
+    t_temp = (-1.0 - line.x0.y)/line.n.y;
+    p = dmnsn_line_point(line, t_temp);
+    if (p.x >= min.x && p.x <= max.x && p.z >= min.z && p.z <= max.z
+        && t_temp >= 0.0 && (t < 0.0 || t_temp < t))
+    {
+      t = t_temp;
+    }
+
+    /* y == 1.0 */
+    t_temp = (1.0 - line.x0.y)/line.n.y;
+    p = dmnsn_line_point(line, t_temp);
+    if (p.x >= min.x && p.x <= max.x && p.z >= min.z && p.z <= max.z
+        && t_temp >= 0.0 && (t < 0.0 || t_temp < t))
+    {
+      t = t_temp;
+    }
+  }
+
+  if (line.n.z != 0.0) {
+    /* z == -1.0 */
+    t_temp = (-1.0 - line.x0.z)/line.n.z;
+    p = dmnsn_line_point(line, t_temp);
+    if (p.x >= min.x && p.x <= max.x && p.y >= min.y && p.y <= max.y
+        && t_temp >= 0.0 && (t < 0.0 || t_temp < t))
+    {
+      t = t_temp;
+    }
+
+    /* z == 1.0 */
+    t_temp = (1.0 - line.x0.z)/line.n.z;
+    p = dmnsn_line_point(line, t_temp);
+    if (p.x >= min.x && p.x <= max.x && p.y >= min.y && p.y <= max.y
+        && t_temp >= 0.0 && (t < 0.0 || t_temp < t))
+    {
+      t = t_temp;
+    }
+  }
+
+  return t;
+}
-- 
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