Support rendering image subregions.

This is the first step to supporting distributed renders.

3 files changed, 19 insertions, 2 deletions

diff --git a/libdimension/dimension/scene.h b/libdimension/dimension/scene.h
index 969fa45..41e2360 100644
--- a/libdimension/dimension/scene.h
+++ b/libdimension/dimension/scene.h
@@ -48,6 +48,12 @@ typedef struct dmnsn_scene {
   /** Canvas. */
   dmnsn_canvas *canvas;
 
+  /* Support for rendering image subregions. */
+  size_t region_x; /**< The x position of the canvas in the broader image. */
+  size_t region_y; /**< The y position of the canvas in the broader image. */
+  size_t outer_width; /**< Width of the broader image. */
+  size_t outer_height; /**< Height of the broader image. */
+
   /** Objects. */
   dmnsn_array *objects;
 
diff --git a/libdimension/raytrace.c b/libdimension/raytrace.c
index 06878fd..cb5c8b6 100644
--- a/libdimension/raytrace.c
+++ b/libdimension/raytrace.c
@@ -184,8 +184,8 @@ dmnsn_raytrace_scene_concurrent(void *ptr, unsigned int thread,
       /* Get the ray corresponding to the (x,y)'th pixel */
       dmnsn_line ray = dmnsn_camera_ray(
         scene->camera,
-        ((double)x)/(scene->canvas->width - 1),
-        ((double)y)/(scene->canvas->height - 1)
+        ((double)(x + scene->region_x))/(scene->outer_width - 1),
+        ((double)(y + scene->region_y))/(scene->outer_height - 1)
       );
 
       /* Shoot a ray */
diff --git a/libdimension/scene.c b/libdimension/scene.c
index ef597ee..f0ff451 100644
--- a/libdimension/scene.c
+++ b/libdimension/scene.c
@@ -37,6 +37,10 @@ dmnsn_new_scene(void)
   scene->default_texture  = dmnsn_new_texture();
   scene->default_interior = dmnsn_new_interior();
   scene->canvas           = NULL;
+  scene->region_x         = 0;
+  scene->region_y         = 0;
+  scene->outer_width      = 0;
+  scene->outer_height     = 0;
   scene->objects          = dmnsn_new_array(sizeof(dmnsn_object *));
   scene->lights           = dmnsn_new_array(sizeof(dmnsn_light *));
   scene->camera           = NULL;
@@ -83,6 +87,13 @@ dmnsn_initialize_scene(dmnsn_scene *scene)
   dmnsn_assert(!scene->initialized, "Texture double-initialized.");
   scene->initialized = true;
 
+  if (scene->outer_width == 0) {
+    scene->outer_width = scene->canvas->width;
+  }
+  if (scene->outer_height == 0) {
+    scene->outer_height = scene->canvas->height;
+  }
+
   dmnsn_initialize_texture(scene->default_texture);
 
   if (scene->sky_sphere) {