From 00997fa54c64b53618255b1e292d3db4d18b86af Mon Sep 17 00:00:00 2001
From: Tavian Barnes <tavianator@gmail.com>
Date: Thu, 16 Jul 2009 01:16:16 +0000
Subject: New dmnsn_intersection* type for ray-object intersections.

---
 libdimension/dimension/object.h |  26 +++++++---
 libdimension/objects.c          | 104 ++++++++++++++++++++++++----------------
 libdimension/raytrace.c         |   9 ++--
 3 files changed, 86 insertions(+), 53 deletions(-)

(limited to 'libdimension')

diff --git a/libdimension/dimension/object.h b/libdimension/dimension/object.h
index 901b366..fefb061 100644
--- a/libdimension/dimension/object.h
+++ b/libdimension/dimension/object.h
@@ -25,12 +25,27 @@
 #ifndef DIMENSION_OBJECT_H
 #define DIMENSION_OBJECT_H
 
+/* A type to represent a ray-object intersection */
+typedef struct {
+  /* The ray and point which intersected */
+  dmnsn_line ray;
+  double t;
+
+  /* The texture at the intersection point */
+  const dmnsn_texture *texture;
+} dmnsn_intersection;
+
+dmnsn_intersection *dmnsn_new_intersection();
+void dmnsn_delete_intersection(dmnsn_intersection *intersection);
+
 /* Forward-declare dmnsn_object */
 typedef struct dmnsn_object dmnsn_object;
 
 /* Object callback types */
-typedef dmnsn_array *dmnsn_object_intersections_fn(const dmnsn_object *object,
-                                                   dmnsn_line line);
+
+typedef dmnsn_intersection *
+dmnsn_object_intersection_fn(const dmnsn_object *object, dmnsn_line line);
+
 typedef int dmnsn_object_inside_fn(const dmnsn_object *object,
                                    dmnsn_vector point);
 
@@ -43,9 +58,9 @@ struct dmnsn_object {
   dmnsn_matrix trans;
 
   /* Callback functions */
-  dmnsn_object_intersections_fn *intersections_fn;
-  dmnsn_object_inside_fn        *inside_fn;
-  dmnsn_free_fn                 *free_fn;
+  dmnsn_object_intersection_fn *intersection_fn;
+  dmnsn_object_inside_fn       *inside_fn;
+  dmnsn_free_fn                *free_fn;
 
   /* Generic pointer for object info */
   void *ptr;
@@ -53,7 +68,6 @@ struct dmnsn_object {
 
 /* Allocate a dummy object */
 dmnsn_object *dmnsn_new_object();
-
 /* Free an object */
 void dmnsn_delete_object(dmnsn_object *object);
 
diff --git a/libdimension/objects.c b/libdimension/objects.c
index 32d3fdd..780c06b 100644
--- a/libdimension/objects.c
+++ b/libdimension/objects.c
@@ -27,8 +27,10 @@
  */
 
 /* Sphere object callbacks */
-static dmnsn_array *dmnsn_sphere_intersections_fn(const dmnsn_object *sphere,
-                                                  dmnsn_line line);
+
+static dmnsn_intersection *
+dmnsn_sphere_intersection_fn(const dmnsn_object *sphere, dmnsn_line line);
+
 static int dmnsn_sphere_inside_fn(const dmnsn_object *sphere,
                                   dmnsn_vector point);
 
@@ -38,18 +40,18 @@ dmnsn_new_sphere()
 {
   dmnsn_object *sphere = dmnsn_new_object();
   if (sphere) {
-    sphere->intersections_fn = &dmnsn_sphere_intersections_fn;
-    sphere->inside_fn        = &dmnsn_sphere_inside_fn;
+    sphere->intersection_fn = &dmnsn_sphere_intersection_fn;
+    sphere->inside_fn       = &dmnsn_sphere_inside_fn;
   }
   return sphere;
 }
 
-/* Return a list of insersections of `line' with a sphere */
-static dmnsn_array *
-dmnsn_sphere_intersections_fn(const dmnsn_object *sphere, dmnsn_line line)
+/* Returns the closest intersection of `line' with `sphere' */
+static dmnsn_intersection *
+dmnsn_sphere_intersection_fn(const dmnsn_object *sphere, dmnsn_line line)
 {
-  double a, b, c, t[2];
-  dmnsn_array *array = dmnsn_new_array(sizeof(double));
+  double a, b, c, t;
+  dmnsn_intersection *intersection = NULL;
 
   /* Solve (x0 + nx*t)^2 + (y0 + ny*t)^2 + (z0 + nz*t)^2 == 1 */
 
@@ -58,13 +60,20 @@ dmnsn_sphere_intersections_fn(const dmnsn_object *sphere, dmnsn_line line)
   c = line.x0.x*line.x0.x + line.x0.y*line.x0.y + line.x0.z*line.x0.z - 1.0;
 
   if (b*b - 4.0*a*c >= 0) {
-    t[0] = (-b + sqrt(b*b - 4.0*a*c))/(2*a);
-    t[1] = (-b - sqrt(b*b - 4.0*a*c))/(2*a);
-    dmnsn_array_set(array, 0, &t[0]);
-    dmnsn_array_set(array, 1, &t[1]);
+    t = (-b - sqrt(b*b - 4.0*a*c))/(2*a);
+    if (t < 0.0) {
+      t = (-b + sqrt(b*b - 4.0*a*c))/(2*a);
+    }
+
+    if (t >= 0.0) {
+      intersection = dmnsn_new_intersection();
+      intersection->ray     = line;
+      intersection->t       = t;
+      intersection->texture = sphere->texture;
+    }
   }
 
-  return array;
+  return intersection;
 }
 
 /* Return whether a point is inside a sphere (x**2 + y**2 + z**2 < 1.0) */
@@ -79,8 +88,8 @@ dmnsn_sphere_inside_fn(const dmnsn_object *sphere, dmnsn_vector point)
  */
 
 /* Cube callbacks */
-static dmnsn_array *dmnsn_cube_intersections_fn(const dmnsn_object *cube,
-                                                  dmnsn_line line);
+static dmnsn_intersection *dmnsn_cube_intersection_fn(const dmnsn_object *cube,
+                                                      dmnsn_line line);
 static int dmnsn_cube_inside_fn(const dmnsn_object *cube,
                                   dmnsn_vector point);
 
@@ -90,71 +99,84 @@ dmnsn_new_cube()
 {
   dmnsn_object *cube = dmnsn_new_object();
   if (cube) {
-    cube->intersections_fn = &dmnsn_cube_intersections_fn;
+    cube->intersection_fn = &dmnsn_cube_intersection_fn;
     cube->inside_fn        = &dmnsn_cube_inside_fn;
   }
   return cube;
 }
 
 /* Intersections callback for a cube */
-static dmnsn_array *
-dmnsn_cube_intersections_fn(const dmnsn_object *cube, dmnsn_line line)
+static dmnsn_intersection *
+dmnsn_cube_intersection_fn(const dmnsn_object *cube, dmnsn_line line)
 {
-  double t;
+  double t = -1.0, t_temp;
   dmnsn_vector p;
-  dmnsn_array *array = dmnsn_new_array(sizeof(double));
+  dmnsn_intersection *intersection = NULL;
 
   /* Six ray-plane intersection tests (x, y, z) = +/- 1.0 */
 
   if (line.n.x != 0.0) {
     /* x = -1.0 */
-    t = (-1.0 - line.x0.x)/line.n.x;
-    p = dmnsn_line_point(line, t);
-    if (p.y >= -1.0 && p.y <= 1.0 && p.z >= -1.0 && p.z <= 1.0) {
-      dmnsn_array_push(array, &t);
+    t_temp = (-1.0 - line.x0.x)/line.n.x;
+    p = dmnsn_line_point(line, t_temp);
+    if (p.y >= -1.0 && p.y <= 1.0 && p.z >= -1.0 && p.z <= 1.0
+        && t_temp >= 0.0 && (t < 0.0 || t_temp < t)) {
+      t = t_temp;
     }
 
     /* x = 1.0 */
-    t = (1.0 - line.x0.x)/line.n.x;
+    t_temp = (1.0 - line.x0.x)/line.n.x;
     p = dmnsn_line_point(line, t);
-    if (p.y >= -1.0 && p.y <= 1.0 && p.z >= -1.0 && p.z <= 1.0) {
-      dmnsn_array_push(array, &t);
+    if (p.y >= -1.0 && p.y <= 1.0 && p.z >= -1.0 && p.z <= 1.0
+        && t_temp >= 0.0 && (t < 0.0 || t_temp < t)) {
+      t = t_temp;
     }
   }
 
   if (line.n.y != 0.0) {
     /* y = -1.0 */
-    t = (-1.0 - line.x0.y)/line.n.y;
+    t_temp = (-1.0 - line.x0.y)/line.n.y;
     p = dmnsn_line_point(line, t);
-    if (p.x >= -1.0 && p.x <= 1.0 && p.z >= -1.0 && p.z <= 1.0) {
-      dmnsn_array_push(array, &t);
+    if (p.y >= -1.0 && p.y <= 1.0 && p.z >= -1.0 && p.z <= 1.0
+        && t_temp >= 0.0 && (t < 0.0 || t_temp < t)) {
+      t = t_temp;
     }
 
     /* y = 1.0 */
-    t = (1.0 - line.x0.y)/line.n.y;
+    t_temp = (1.0 - line.x0.y)/line.n.y;
     p = dmnsn_line_point(line, t);
-    if (p.x >= -1.0 && p.x <= 1.0 && p.z >= -1.0 && p.z <= 1.0) {
-      dmnsn_array_push(array, &t);
+    if (p.y >= -1.0 && p.y <= 1.0 && p.z >= -1.0 && p.z <= 1.0
+        && t_temp >= 0.0 && (t < 0.0 || t_temp < t)) {
+      t = t_temp;
     }
   }
 
   if (line.n.z != 0.0) {
     /* z = -1.0 */
-    t = (-1.0 - line.x0.z)/line.n.z;
+    t_temp = (-1.0 - line.x0.z)/line.n.z;
     p = dmnsn_line_point(line, t);
-    if (p.x >= -1.0 && p.x <= 1.0 && p.y >= -1.0 && p.y <= 1.0) {
-      dmnsn_array_push(array, &t);
+    if (p.y >= -1.0 && p.y <= 1.0 && p.z >= -1.0 && p.z <= 1.0
+        && t_temp >= 0.0 && (t < 0.0 || t_temp < t)) {
+      t = t_temp;
     }
 
     /* z = 1.0 */
-    t = (1.0 - line.x0.z)/line.n.z;
+    t_temp = (1.0 - line.x0.z)/line.n.z;
     p = dmnsn_line_point(line, t);
-    if (p.x >= -1.0 && p.x <= 1.0 && p.y >= -1.0 && p.y <= 1.0) {
-      dmnsn_array_push(array, &t);
+    if (p.y >= -1.0 && p.y <= 1.0 && p.z >= -1.0 && p.z <= 1.0
+        && t_temp >= 0.0 && (t < 0.0 || t_temp < t)) {
+      t = t_temp;
     }
   }
 
-  return array;
+  if (t >= 0.0) {
+    intersection = dmnsn_new_intersection();
+    intersection->ray     = line;
+    intersection->t       = t;
+    intersection->texture = cube->texture;
+  }
+
+  return intersection;
 }
 
 /* Inside callback for a cube */
diff --git a/libdimension/raytrace.c b/libdimension/raytrace.c
index 03dcbab..75e857c 100644
--- a/libdimension/raytrace.c
+++ b/libdimension/raytrace.c
@@ -230,7 +230,7 @@ dmnsn_raytrace_shoot(dmnsn_scene *scene, dmnsn_color color,
 {
   dmnsn_line ray, ray_trans;
   dmnsn_object *object;
-  dmnsn_array *intersections;
+  dmnsn_intersection *intersection;
   unsigned int i;
 
   /* Get the ray corresponding to the (x,y)'th pixel */
@@ -243,14 +243,11 @@ dmnsn_raytrace_shoot(dmnsn_scene *scene, dmnsn_color color,
     ray_trans = dmnsn_matrix_line_mul(object->trans, ray);
 
     /* Test for intersections with objects */
-    intersections = (*object->intersections_fn)(object, ray_trans);
+    intersection = (*object->intersection_fn)(object, ray_trans);
 
-    if (dmnsn_array_size(intersections) > 0) {
+    if (intersection) {
       color = dmnsn_color_from_XYZ(dmnsn_whitepoint);
     }
-
-    /* Delete the intersections array */
-    dmnsn_delete_array(intersections);
   }
 
   return color;
-- 
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