Add lots of comments, and some code fixes discovered in the process.

26 files changed, 177 insertions, 79 deletions

diff --git a/libdimension/array.c b/libdimension/array.c
index f8f3c58..82588aa 100644
--- a/libdimension/array.c
+++ b/libdimension/array.c
@@ -26,6 +26,7 @@
 static void dmnsn_array_get_impl(const dmnsn_array *array, size_t i, void *obj);
 static void dmnsn_array_set_impl(dmnsn_array *array, size_t i, const void *obj);
 
+/* Allocate a new array - guaranteed not to fail if it returns */
 dmnsn_array *
 dmnsn_new_array(size_t obj_size)
 {
@@ -35,11 +36,13 @@ dmnsn_new_array(size_t obj_size)
     array->length   = 0;
     array->capacity = 4; /* Start with capacity of 4 */
 
+    /* Allocate the memory */
     array->ptr = malloc(array->capacity*array->obj_size);
     if (!array->ptr) {
       dmnsn_error(DMNSN_SEVERITY_HIGH, "Array allocation failed.");
     }
 
+    /* Allocate the read-write lock */
     array->rwlock = malloc(sizeof(pthread_rwlock_t));
     if (!array->rwlock || pthread_rwlock_init(array->rwlock, NULL) != 0) {
       dmnsn_error(DMNSN_SEVERITY_HIGH, "Array rwlock allocation failed.");
@@ -49,6 +52,7 @@ dmnsn_new_array(size_t obj_size)
   return array;
 }
 
+/* Delete the array */
 void dmnsn_delete_array(dmnsn_array *array) {
   if (array) {
     if (pthread_rwlock_destroy(array->rwlock) != 0) {
@@ -61,6 +65,7 @@ void dmnsn_delete_array(dmnsn_array *array) {
   }
 }
 
+/* Push obj to the end of the array, atomically */
 void
 dmnsn_array_push(dmnsn_array *array, const void *obj)
 {
@@ -69,6 +74,7 @@ dmnsn_array_push(dmnsn_array *array, const void *obj)
   dmnsn_array_unlock(array);
 }
 
+/* Pop obj from the end of the array, atomically */
 void
 dmnsn_array_pop(dmnsn_array *array, void *obj)
 {
@@ -76,11 +82,12 @@ dmnsn_array_pop(dmnsn_array *array, void *obj)
 
   dmnsn_array_wrlock(array);
     size = dmnsn_array_size_unlocked(array);
-    dmnsn_array_get_impl(array, size - 1, obj);
-    dmnsn_array_resize_unlocked(array, size - 1);
+    dmnsn_array_get_impl(array, size - 1, obj);   /* Copy the object */
+    dmnsn_array_resize_unlocked(array, size - 1); /* Shrink the array */
   dmnsn_array_unlock(array);
 }
 
+/* Get the i'th object, bailing out if i is out of range */
 void
 dmnsn_array_get(const dmnsn_array *array, size_t i, void *obj)
 {
@@ -89,6 +96,7 @@ dmnsn_array_get(const dmnsn_array *array, size_t i, void *obj)
   dmnsn_array_unlock(array);
 }
 
+/* Set the i'th object, expanding the array if necessary */
 void
 dmnsn_array_set(dmnsn_array *array, size_t i, const void *obj)
 {
@@ -97,6 +105,7 @@ dmnsn_array_set(dmnsn_array *array, size_t i, const void *obj)
   dmnsn_array_unlock(array);
 }
 
+/* Get the size of the array, atomically */
 size_t
 dmnsn_array_size(const dmnsn_array *array)
 {
@@ -109,6 +118,7 @@ dmnsn_array_size(const dmnsn_array *array)
   return size;
 }
 
+/* Set the size of the array, atomically */
 void
 dmnsn_array_resize(dmnsn_array *array, size_t length)
 {
@@ -117,6 +127,7 @@ dmnsn_array_resize(dmnsn_array *array, size_t length)
   dmnsn_array_unlock(array);
 }
 
+/* Thread-unsafe range-checked element access */
 void *
 dmnsn_array_at(dmnsn_array *array, size_t i)
 {
@@ -126,16 +137,19 @@ dmnsn_array_at(dmnsn_array *array, size_t i)
   return (char *)array->ptr + array->obj_size*i;
 }
 
+/* Get the size non-atomically, for manual locking */
 size_t
 dmnsn_array_size_unlocked(const dmnsn_array *array)
 {
   return array->length;
 }
 
+/* Set the size non-atomically, for manual locking */
 void
 dmnsn_array_resize_unlocked(dmnsn_array *array, size_t length)
 {
   if (length > array->capacity) {
+    /* Resize if we don't have enough capacity */
     array->capacity = length*2; /* We are greedy */
     array->ptr = realloc(array->ptr, array->obj_size*array->capacity);
     if (!array->ptr) {
@@ -146,6 +160,7 @@ dmnsn_array_resize_unlocked(dmnsn_array *array, size_t length)
   array->length = length;
 }
 
+/* Set a manual read-lock */
 void
 dmnsn_array_rdlock(const dmnsn_array *array)
 {
@@ -157,6 +172,7 @@ dmnsn_array_rdlock(const dmnsn_array *array)
   }
 }
 
+/* Set a manual write-lock */
 void
 dmnsn_array_wrlock(dmnsn_array *array)
 {
@@ -168,6 +184,7 @@ dmnsn_array_wrlock(dmnsn_array *array)
   }
 }
 
+/* Unset a manual lock */
 void
 dmnsn_array_unlock(const dmnsn_array *array)
 {
@@ -178,19 +195,23 @@ dmnsn_array_unlock(const dmnsn_array *array)
   }
 }
 
+/* Actual "get" implementation */
 static void
 dmnsn_array_get_impl(const dmnsn_array *array, size_t i, void *obj)
 {
   if (i >= dmnsn_array_size_unlocked(array)) {
+    /* Range check failed */
     dmnsn_error(DMNSN_SEVERITY_HIGH, "Array index out of bounds.");
   }
   memcpy(obj, array->ptr + array->obj_size*i, array->obj_size);
 }
 
+/* Actual "set" implementation */
 static void
 dmnsn_array_set_impl(dmnsn_array *array, size_t i, const void *obj)
 {
   if (i >= dmnsn_array_size_unlocked(array)) {
+    /* Resize if i is out of range */
     dmnsn_array_resize_unlocked(array, i + 1);
   }
   memcpy(array->ptr + array->obj_size*i, obj, array->obj_size);
diff --git a/libdimension/camera.c b/libdimension/camera.c
index 282daaf..c353cbe 100644
--- a/libdimension/camera.c
+++ b/libdimension/camera.c
@@ -21,12 +21,14 @@
 #include "dimension.h"
 #include <stdlib.h> /* For malloc */
 
+/* Allocate a new dummy camera */
 dmnsn_camera *
 dmnsn_new_camera()
 {
   return malloc(sizeof(dmnsn_camera));
 }
 
+/* Free a dummy camera */
 void
 dmnsn_delete_camera(dmnsn_camera *camera)
 {
@@ -35,11 +37,15 @@ dmnsn_delete_camera(dmnsn_camera *camera)
 
 /* Perspective camera */
 
+/* Perspective camera ray callback */
 static dmnsn_line dmnsn_perspective_camera_ray_fn(const dmnsn_camera *camera,
                                                   const dmnsn_canvas *canvas,
                                                   unsigned int x,
                                                   unsigned int y);
 
+/* Create a new perspective camera.  Rays are aimed from the origin to a screen
+   located on the z = 1 frame, from (-0.5, -0.5) to (0.5, 0.5).  Rays are then
+   transformed by the matrix `trans'. */
 dmnsn_camera *
 dmnsn_new_perspective_camera(dmnsn_matrix trans)
 {
@@ -57,6 +63,7 @@ dmnsn_new_perspective_camera(dmnsn_matrix trans)
   return camera;
 }
 
+/* Delete a perspective camera */
 void
 dmnsn_delete_perspective_camera(dmnsn_camera *camera)
 {
@@ -74,7 +81,10 @@ dmnsn_perspective_camera_ray_fn(const dmnsn_camera *camera,
   dmnsn_matrix *trans = (dmnsn_matrix *)camera->ptr;
   dmnsn_line l;
 
+  /* Rays originate at the origin, oddly enough */
   l.x0 = dmnsn_vector_construct(0.0, 0.0, 0.0);
+
+  /* Aim at the z = 1 plane */
   l.n.x = ((double)x)/(canvas->x - 1) - 0.5;
   l.n.y = ((double)y)/(canvas->y - 1) - 0.5;
   l.n.z = 1.0;
diff --git a/libdimension/canvas.c b/libdimension/canvas.c
index 516c978..13b1e9e 100644
--- a/libdimension/canvas.c
+++ b/libdimension/canvas.c
@@ -32,8 +32,6 @@ dmnsn_new_canvas(unsigned int x, unsigned int y)
   dmnsn_canvas *canvas = malloc(sizeof(dmnsn_canvas));
 
   if (canvas) {
-    /* *canvas exists */
-
     /* Set the width and height */
     canvas->x = x;
     canvas->y = y;
@@ -60,6 +58,7 @@ dmnsn_new_canvas(unsigned int x, unsigned int y)
           /* pthread_rwlock_init failed.  Destroy the locks we've already made,
              free the canvas, and return NULL.  We leak memory if destruction
              fails (i.e. someone is somehow using an rwlock already). */
+
           for (l = 0; l < j; ++l) {
             for (k = 0; k < x; ++k) {
               if (pthread_rwlock_destroy(&canvas->rwlocks[l*x + k]) != 0) {
@@ -96,8 +95,6 @@ dmnsn_delete_canvas(dmnsn_canvas *canvas)
   unsigned int i, j;
 
   if (canvas) {
-    /* *canvas exists */
-
     /* Destroy the rwlocks */
     for (i = 0; i < canvas->x; ++i) {
       for (j = 0; j < canvas->y; ++j) {
@@ -121,7 +118,7 @@ dmnsn_get_pixel(const dmnsn_canvas *canvas, unsigned int x, unsigned int y)
 {
   dmnsn_color color;
   dmnsn_rdlock_pixel(canvas, x, y);
-  color = canvas->pixels[y*canvas->x + x];
+    color = canvas->pixels[y*canvas->x + x];
   dmnsn_unlock_pixel(canvas, x, y);
   return color;
 }
@@ -132,7 +129,7 @@ dmnsn_set_pixel(dmnsn_canvas *canvas,
                 unsigned int x, unsigned int y, dmnsn_color color)
 {
   dmnsn_wrlock_pixel(canvas, x, y);
-  canvas->pixels[y*canvas->x + x] = color;
+    canvas->pixels[y*canvas->x + x] = color;
   dmnsn_unlock_pixel(canvas, x, y);
 }
 
diff --git a/libdimension/color.c b/libdimension/color.c
index 42ade8b..4aede1f 100644
--- a/libdimension/color.c
+++ b/libdimension/color.c
@@ -21,7 +21,7 @@
 #include "dimension.h"
 #include <math.h> /* For pow(), sqrt() */
 
-/* sRGB white point (D50) */
+/* sRGB white point (CIE D50) */
 const dmnsn_CIE_XYZ dmnsn_whitepoint = { .X = 0.9504060171449392,
                                          .Y = 0.9999085943425312,
                                          .Z = 1.089062231497274 };
@@ -42,7 +42,8 @@ dmnsn_color_from_xyY(dmnsn_CIE_xyY xyY)
   dmnsn_color ret = { .X = xyY.Y*xyY.x/xyY.y,
                       .Y = xyY.Y,
                       .Z = xyY.Y*(1.0 - xyY.x - xyY.y)/xyY.y,
-                      .filter = 0.0, .trans = 0.0 };
+                      .filter = 0.0,
+                      .trans = 0.0 };
   return ret;
 }
 
@@ -267,6 +268,7 @@ dmnsn_color_add(dmnsn_color color1, dmnsn_color color2)
   Lab.b = Lab1.b + Lab2.b;
 
   ret = dmnsn_color_from_Lab(Lab, dmnsn_whitepoint);
+  /* Waited average of transparencies by intensity */
   ret.filter = (Lab1.L*color1.filter + Lab2.L*color2.filter)/Lab.L;
   ret.trans  = (Lab1.L*color1.trans  + Lab2.L*color2.trans)/Lab.L;
 
diff --git a/libdimension/cube.c b/libdimension/cube.c
index 197a0f8..bb71d0b 100644
--- a/libdimension/cube.c
+++ b/libdimension/cube.c
@@ -27,6 +27,7 @@ static dmnsn_array *dmnsn_cube_intersections_fn(const dmnsn_object *cube,
 static int dmnsn_cube_inside_fn(const dmnsn_object *cube,
                                   dmnsn_vector point);
 
+/* Allocate a new cube object */
 dmnsn_object *
 dmnsn_new_cube()
 {
@@ -38,12 +39,14 @@ dmnsn_new_cube()
   return cube;
 }
 
+/* Delete a cube */
 void
 dmnsn_delete_cube(dmnsn_object *cube)
 {
   dmnsn_delete_object(cube);
 }
 
+/* Intersections callback for a cube */
 static dmnsn_array *
 dmnsn_cube_intersections_fn(const dmnsn_object *cube, dmnsn_line line)
 {
@@ -104,6 +107,7 @@ dmnsn_cube_intersections_fn(const dmnsn_object *cube, dmnsn_line line)
   return array;
 }
 
+/* Inside callback for a cube */
 static int
 dmnsn_cube_inside_fn(const dmnsn_object *cube, dmnsn_vector point)
 {
diff --git a/libdimension/dimension.h b/libdimension/dimension.h
index 5820200..5e262e3 100644
--- a/libdimension/dimension.h
+++ b/libdimension/dimension.h
@@ -18,6 +18,10 @@
  * <http://www.gnu.org/licenses/>.                                       *
  *************************************************************************/
 
+/*
+ * libdimension - a library for photo-realistic 3-D rendering
+ */
+
 #ifndef DIMENSION_H
 #define DIMENSION_H
 
diff --git a/libdimension/dimension/array.h b/libdimension/dimension/array.h
index d0693fc..0af4406 100644
--- a/libdimension/dimension/array.h
+++ b/libdimension/dimension/array.h
@@ -18,14 +18,14 @@
  * <http://www.gnu.org/licenses/>.                                       *
  *************************************************************************/
 
-#ifndef DIMENSION_ARRAY_H
-#define DIMENSION_ARRAY_H
-
 /*
  * Simple thread-safe generalized arrays, for returning variable-length arrays
  * from functions, and other fun stuff.
  */
 
+#ifndef DIMENSION_ARRAY_H
+#define DIMENSION_ARRAY_H
+
 #include <pthread.h> /* For pthread_rwlock_t */
 #include <stdlib.h>  /* For size_t */
 
@@ -37,24 +37,26 @@ typedef struct {
   pthread_rwlock_t *rwlock;
 } dmnsn_array;
 
+/* Array allocation never returns NULL - if dmnsn_new_array, it succeeded */
 dmnsn_array *dmnsn_new_array(size_t obj_size);
 void dmnsn_delete_array(dmnsn_array *array);
 
+/* Thread-safe atomic array access */
+
 void dmnsn_array_push(dmnsn_array *array, const void *obj);
 void dmnsn_array_pop(dmnsn_array *array, void *obj);
-
 void dmnsn_array_get(const dmnsn_array *array, size_t i, void *obj);
 void dmnsn_array_set(dmnsn_array *array, size_t i, const void *obj);
 
 size_t dmnsn_array_size(const dmnsn_array *array);
 void   dmnsn_array_resize(dmnsn_array *array, size_t length);
 
-/* Manual locking */
-
+/* Non-atomic operations for manual locking */
 void *dmnsn_array_at(dmnsn_array *array, size_t i);
 size_t dmnsn_array_size_unlocked(const dmnsn_array *array);
 void dmnsn_array_resize_unlocked(dmnsn_array *array, size_t length);
 
+/* Manual locking */
 void dmnsn_array_rdlock(const dmnsn_array *array);
 void dmnsn_array_wrlock(dmnsn_array *array);
 void dmnsn_array_unlock(const dmnsn_array *array);
diff --git a/libdimension/dimension/camera.h b/libdimension/dimension/camera.h
index 95b36fa..9b06359 100644
--- a/libdimension/dimension/camera.h
+++ b/libdimension/dimension/camera.h
@@ -18,13 +18,13 @@
  * <http://www.gnu.org/licenses/>.                                       *
  *************************************************************************/
 
-#ifndef DIMENSION_CAMERA_H
-#define DIMENSION_CAMERA_H
-
 /*
  * A camera.
  */
 
+#ifndef DIMENSION_CAMERA_H
+#define DIMENSION_CAMERA_H
+
 /* Forward-declare dmnsn_camera */
 typedef struct dmnsn_camera dmnsn_camera;
 
@@ -47,7 +47,6 @@ void dmnsn_delete_camera(dmnsn_camera *camera);
 /* A perspective camera, at the origin, looking at (0, 0, 1).  The feild of view
    is the section of the plane z = 1 from (-0.5, -0.5) to (0.5, 0.5).  Rays are
    transformed by the transformation matrix `trans'. */
-
 dmnsn_camera *dmnsn_new_perspective_camera(dmnsn_matrix trans);
 void dmnsn_delete_perspective_camera(dmnsn_camera *camera);
 
diff --git a/libdimension/dimension/canvas.h b/libdimension/dimension/canvas.h
index f05264b..50cc612 100644
--- a/libdimension/dimension/canvas.h
+++ b/libdimension/dimension/canvas.h
@@ -18,14 +18,15 @@
  * <http://www.gnu.org/licenses/>.                                       *
  *************************************************************************/
 
+/*
+ * A canvas which is rendered to.
+ */
+
 #ifndef DIMENSION_CANVAS_H
 #define DIMENSION_CANVAS_H
 
 #include <pthread.h>
 
-/*
- * A canvas which is rendered to.
- */
 typedef struct {
   unsigned int x, y;
 
diff --git a/libdimension/dimension/color.h b/libdimension/dimension/color.h
index ab6efa3..f1964c3 100644
--- a/libdimension/dimension/color.h
+++ b/libdimension/dimension/color.h
@@ -18,13 +18,13 @@
  * <http://www.gnu.org/licenses/>.                                       *
  *************************************************************************/
 
-#ifndef DIMENSION_COLOR_H
-#define DIMENSION_COLOR_H
-
 /*
  * Types to represent color.
  */
 
+#ifndef DIMENSION_COLOR_H
+#define DIMENSION_COLOR_H
+
 /* Internally, we use CIE 1931 XYZ color. */
 typedef struct {
   double X, Y, Z;
diff --git a/libdimension/dimension/cube.h b/libdimension/dimension/cube.h
index e7f2b90..e55ec74 100644
--- a/libdimension/dimension/cube.h
+++ b/libdimension/dimension/cube.h
@@ -18,13 +18,13 @@
  * <http://www.gnu.org/licenses/>.                                       *
  *************************************************************************/
 
-#ifndef DIMENSION_CUBE_H
-#define DIMENSION_CUBE_H
-
 /*
  * A cube, axis-aligned, from (-1, -1, -1) to (1, 1, 1)
  */
 
+#ifndef DIMENSION_CUBE_H
+#define DIMENSION_CUBE_H
+
 dmnsn_object *dmnsn_new_cube();
 void dmnsn_delete_cube(dmnsn_object *cube);
 
diff --git a/libdimension/dimension/error.h b/libdimension/dimension/error.h
index 3204cb2..cd7dd81 100644
--- a/libdimension/dimension/error.h
+++ b/libdimension/dimension/error.h
@@ -18,23 +18,26 @@
  * <http://www.gnu.org/licenses/>.                                       *
  *************************************************************************/
 
-#ifndef DIMENSION_ERROR_H
-#define DIMENSION_ERROR_H
-
 /*
- * Error handling.
+ * Error handling.  Errors are reported at a given severity by the dmnsn_error()
+ * macro at a given severity, which prints a warning if it is below the set
+ * resilience, or prints an error and exits if it's at or above the set
+ * resilience.
  */
 
+#ifndef DIMENSION_ERROR_H
+#define DIMENSION_ERROR_H
+
 typedef enum {
   DMNSN_SEVERITY_LOW,    /* Only die on low resilience */
   DMNSN_SEVERITY_MEDIUM, /* Die on low or medium resilience */
   DMNSN_SEVERITY_HIGH    /* Always die */
 } dmnsn_severity;
 
-/* Use this to report an error */
-#define dmnsn_error(severity, str)                                            \
-  dmnsn_report_error((dmnsn_severity)severity, __PRETTY_FUNCTION__, __LINE__, \
-                     str)
+/* Use this macro to report an error */
+#define dmnsn_error(severity, str)                                             \
+  dmnsn_report_error((dmnsn_severity)(severity), __PRETTY_FUNCTION__, __LINE__,\
+                     (str))
 
 /* Called by dmnsn_error() - don't call directly */
 void dmnsn_report_error(dmnsn_severity severity,
diff --git a/libdimension/dimension/geometry.h b/libdimension/dimension/geometry.h
index 95692c6..c635fd9 100644
--- a/libdimension/dimension/geometry.h
+++ b/libdimension/dimension/geometry.h
@@ -19,7 +19,7 @@
  *************************************************************************/
 
 /*
- * Core geometric types like scalars, vectors, and rays.
+ * Core geometric types like vectors, matricies, and rays.
  */
 
 #ifndef DIMENSION_GEOMETRY_H
@@ -73,6 +73,6 @@ dmnsn_line   dmnsn_matrix_line_mul(dmnsn_matrix lhs, dmnsn_line rhs);
 /* A point on a line, defined by x0 + t*n */
 dmnsn_vector dmnsn_line_point(dmnsn_line l, double t);
 /* Solve for the t value such that x0 + t*n = x */
-double       dmnsn_line_index(dmnsn_line l, dmnsn_vector x);
+double dmnsn_line_index(dmnsn_line l, dmnsn_vector x);
 
 #endif /* DIMENSION_GEOMETRY_H */
diff --git a/libdimension/dimension/object.h b/libdimension/dimension/object.h
index 589ac29..d18f426 100644
--- a/libdimension/dimension/object.h
+++ b/libdimension/dimension/object.h
@@ -18,13 +18,13 @@
  * <http://www.gnu.org/licenses/>.                                       *
  *************************************************************************/
 
-#ifndef DIMENSION_OBJECT_H
-#define DIMENSION_OBJECT_H
-
 /*
  * Objects.
  */
 
+#ifndef DIMENSION_OBJECT_H
+#define DIMENSION_OBJECT_H
+
 /* Forward-declare dmnsn_object */
 typedef struct dmnsn_object dmnsn_object;
 
@@ -46,6 +46,7 @@ struct dmnsn_object {
   dmnsn_object_inside_fn        *inside_fn;
 };
 
+/* Allocate a dummy object */
 dmnsn_object *dmnsn_new_object();
 void dmnsn_delete_object(dmnsn_object *object);
 
diff --git a/libdimension/dimension/png.h b/libdimension/dimension/png.h
index 05ff79a..858f79f 100644
--- a/libdimension/dimension/png.h
+++ b/libdimension/dimension/png.h
@@ -18,6 +18,10 @@
  * <http://www.gnu.org/licenses/>.                                       *
  *************************************************************************/
 
+/*
+ * Support for exporting/importing canvases to/from PNG files
+ */
+
 #ifndef DIMENSION_PNG_H
 #define DIMENSION_PNG_H
 
diff --git a/libdimension/dimension/progress.h b/libdimension/dimension/progress.h
index a865c8f..7958ab9 100644
--- a/libdimension/dimension/progress.h
+++ b/libdimension/dimension/progress.h
@@ -18,6 +18,13 @@
  * <http://www.gnu.org/licenses/>.                                       *
  *************************************************************************/
 
+/*
+ * An interface for asynchronous tasks.  *_async() versions of functions
+ * return a dmnsn_progress* object which can indicate the progress of the
+ * background task, and wait for task completion.  The task's return value
+ * is returned as an int from dmnsn_finish_progress().
+ */
+
 #ifndef DIMENSION_PROGRESS_H
 #define DIMENSION_PROGRESS_H
 
@@ -43,6 +50,7 @@ typedef struct {
 } dmnsn_progress;
 
 dmnsn_progress *dmnsn_new_progress();
+/* For failed returns from *_async() functions */
 void dmnsn_delete_progress(dmnsn_progress *progress);
 
 /* This joins the worker thread and returns it's integer return value in
@@ -50,10 +58,14 @@ void dmnsn_delete_progress(dmnsn_progress *progress);
 int dmnsn_finish_progress(dmnsn_progress *progress);
 
 double dmnsn_get_progress(const dmnsn_progress *progress);
+/* Wait for the progress to be >= prog, in a better way than spinlocking */
 void dmnsn_wait_progress(const dmnsn_progress *progress, double prog);
 
+/* Create a new level of loop nesting */
 void dmnsn_new_progress_element(dmnsn_progress *progress, unsigned int total);
+/* Increment the progress counter; should only be called from innermost loop */
 void dmnsn_increment_progress(dmnsn_progress *progress);
-void dmnsn_progress_done(dmnsn_progress *progress);
+/* Instantly complete the progress */
+void dmnsn_done_progress(dmnsn_progress *progress);
 
 #endif /* DIMENSION_PROGRESS_H */
diff --git a/libdimension/dimension/raytrace.h b/libdimension/dimension/raytrace.h
index a69bb72..b58a39b 100644
--- a/libdimension/dimension/raytrace.h
+++ b/libdimension/dimension/raytrace.h
@@ -18,6 +18,10 @@
  * <http://www.gnu.org/licenses/>.                                       *
  *************************************************************************/
 
+/*
+ * Render a scene by raytracing
+ */
+
 #ifndef DIMENSION_RAYTRACE_H
 #define DIMENSION_RAYTRACE_H
 
diff --git a/libdimension/dimension/scene.h b/libdimension/dimension/scene.h
index a6f2e5d..35087a7 100644
--- a/libdimension/dimension/scene.h
+++ b/libdimension/dimension/scene.h
@@ -18,13 +18,13 @@
  * <http://www.gnu.org/licenses/>.                                       *
  *************************************************************************/
 
-#ifndef DIMENSION_SCENE_H
-#define DIMENSION_SCENE_H
-
 /*
  * A scene.
  */
 
+#ifndef DIMENSION_SCENE_H
+#define DIMENSION_SCENE_H
+
 typedef struct {
   dmnsn_color background;
   dmnsn_array *objects;
diff --git a/libdimension/dimension/sphere.h b/libdimension/dimension/sphere.h
index 2547965..d7a8f54 100644
--- a/libdimension/dimension/sphere.h
+++ b/libdimension/dimension/sphere.h
@@ -18,13 +18,13 @@
  * <http://www.gnu.org/licenses/>.                                       *
  *************************************************************************/
 
-#ifndef DIMENSION_SPHERE_H
-#define DIMENSION_SPHERE_H
-
 /*
  * A sphere object, of radius 1, centered at the origin.
  */
 
+#ifndef DIMENSION_SPHERE_H
+#define DIMENSION_SPHERE_H
+
 dmnsn_object *dmnsn_new_sphere();
 void dmnsn_delete_sphere(dmnsn_object *sphere);
 
diff --git a/libdimension/error.c b/libdimension/error.c
index a8c7ec7..df3ade3 100644
--- a/libdimension/error.c
+++ b/libdimension/error.c
@@ -63,6 +63,7 @@ dmnsn_get_resilience()
   return resilience;
 }
 
+/* Set the resilience, thread-safely */
 void
 dmnsn_set_resilience(dmnsn_severity resilience)
 {
diff --git a/libdimension/object.c b/libdimension/object.c
index 75a82b6..dddcd61 100644
--- a/libdimension/object.c
+++ b/libdimension/object.c
@@ -21,6 +21,7 @@
 #include "dimension.h"
 #include <stdlib.h> /* For malloc */
 
+/* Allocate a dummy object */
 dmnsn_object *
 dmnsn_new_object()
 {
@@ -31,6 +32,7 @@ dmnsn_new_object()
   return object;
 }
 
+/* Free a dummy object */
 void
 dmnsn_delete_object(dmnsn_object *object)
 {
diff --git a/libdimension/png.c b/libdimension/png.c
index b8cfabc..6bb1f13 100644
--- a/libdimension/png.c
+++ b/libdimension/png.c
@@ -25,6 +25,8 @@
 #include <arpa/inet.h>
 #include <stdlib.h>
 
+/* Payload to store function arguments for thread callbacks */
+
 typedef struct {
   dmnsn_progress *progress;
   const dmnsn_canvas *canvas;
@@ -37,6 +39,7 @@ typedef struct {
   FILE *file;
 } dmnsn_png_read_payload;
 
+/* Thread callbacks */
 static void *dmnsn_png_write_canvas_thread(void *ptr);
 static void *dmnsn_png_read_canvas_thread(void *ptr);
 
@@ -67,11 +70,11 @@ dmnsn_png_write_canvas_async(const dmnsn_canvas *canvas, FILE *file)
     payload->canvas   = canvas;
     payload->file     = file;
 
+    /* Create the worker thread */
     if (pthread_create(&progress->thread, NULL, &dmnsn_png_write_canvas_thread,
                        payload)
         != 0) {
-      dmnsn_error(DMNSN_SEVERITY_MEDIUM,
-                  "Creating png writing worker thread failed.");
+      free(payload);
       dmnsn_delete_progress(progress);
       return NULL;
     }
@@ -108,11 +111,11 @@ dmnsn_png_read_canvas_async(dmnsn_canvas **canvas, FILE *file)
     payload->canvas   = canvas;
     payload->file     = file;
 
+    /* Create the worker thread */
     if (pthread_create(&progress->thread, NULL, &dmnsn_png_read_canvas_thread,
                        payload)
         != 0) {
-      dmnsn_error(DMNSN_SEVERITY_MEDIUM,
-                  "Creating png writing worker thread failed.");
+      free(payload);
       dmnsn_delete_progress(progress);
       return NULL;
     }
@@ -121,10 +124,14 @@ dmnsn_png_read_canvas_async(dmnsn_canvas **canvas, FILE *file)
   return progress;
 }
 
+/* Actual implementations */
 static int dmnsn_png_write_canvas_impl(dmnsn_progress *progress,
                                        const dmnsn_canvas *canvas, FILE *file);
 static dmnsn_canvas *dmnsn_png_read_canvas_impl(dmnsn_progress *progress,
                                                 FILE *file);
+
+/* Thread callbacks */
+
 static void *
 dmnsn_png_write_canvas_thread(void *ptr)
 {
@@ -134,7 +141,8 @@ dmnsn_png_write_canvas_thread(void *ptr)
     *retval = dmnsn_png_write_canvas_impl(payload->progress,
                                           payload->canvas, payload->file);
   }
-  dmnsn_progress_done(payload->progress);
+  dmnsn_done_progress(payload->progress);
+  free(payload);
   return retval;
 }
 
@@ -146,12 +154,14 @@ dmnsn_png_read_canvas_thread(void *ptr)
   if (retval) {
     *payload->canvas = dmnsn_png_read_canvas_impl(payload->progress,
                                                   payload->file);
-    *retval = payload->canvas ? 0 : 1;
+    *retval = payload->canvas ? 0 : 1; /* Fail if it returned NULL */
   }
-  dmnsn_progress_done(payload->progress);
+  dmnsn_done_progress(payload->progress);
+  free(payload);
   return retval;
 }
 
+/* Actually write the PNG file */
 static int
 dmnsn_png_write_canvas_impl(dmnsn_progress *progress,
                             const dmnsn_canvas *canvas, FILE *file)
@@ -272,9 +282,11 @@ static pthread_key_t progress_key;
 static pthread_mutex_t progress_mutex = PTHREAD_MUTEX_INITIALIZER;
 static int progress_key_init = 0;
 
+/* Callback to increment the progress after a row has been read */
 static void dmnsn_png_read_row_callback(png_structp png_ptr, png_uint_32 row,
                                         int pass);
 
+/* Actually read a PNG file */
 static dmnsn_canvas *
 dmnsn_png_read_canvas_impl(dmnsn_progress *progress, FILE *file)
 {
@@ -301,9 +313,7 @@ dmnsn_png_read_canvas_impl(dmnsn_progress *progress, FILE *file)
 
   if (progress_key_init == 0) {
     if (pthread_key_create(&progress_key, NULL) != 0) {
-      /* High severity because dmnsn_png_read_row_callback will surely segfault
-         if it can't get the dmnsn_progress* from the key */
-      dmnsn_error(DMNSN_SEVERITY_HIGH,
+      dmnsn_error(DMNSN_SEVERITY_MEDIUM,
                   "Couldn't create thread-specific pointer.");
     }
 
@@ -311,7 +321,7 @@ dmnsn_png_read_canvas_impl(dmnsn_progress *progress, FILE *file)
   }
 
   if (pthread_setspecific(progress_key, progress) != 0) {
-    dmnsn_error(DMNSN_SEVERITY_HIGH, "Couldn't set thread-specific pointer.");
+    dmnsn_error(DMNSN_SEVERITY_MEDIUM, "Couldn't set thread-specific pointer.");
   }
 
   if (pthread_mutex_unlock(&progress_mutex) != 0) {
@@ -506,5 +516,7 @@ static void
 dmnsn_png_read_row_callback(png_structp png_ptr, png_uint_32 row, int pass)
 {
   dmnsn_progress *progress = pthread_getspecific(progress_key);
-  dmnsn_increment_progress(progress);
+  if (progress) {
+    dmnsn_increment_progress(progress);
+  }
 }
\ No newline at end of file
diff --git a/libdimension/progress.c b/libdimension/progress.c
index 29469a6..f25af74 100644
--- a/libdimension/progress.c
+++ b/libdimension/progress.c
@@ -32,6 +32,8 @@ dmnsn_new_progress()
     progress->elements = dmnsn_new_array(sizeof(dmnsn_progress_element));
     dmnsn_array_push(progress->elements, &element);
 
+    /* Allocate space for the condition variable and mutex */
+
     progress->cond = malloc(sizeof(pthread_cond_t));
     if (!progress->cond) {
       dmnsn_delete_array(progress->elements);
@@ -139,22 +141,22 @@ void
 dmnsn_wait_progress(const dmnsn_progress *progress, double prog)
 {
   if (pthread_mutex_lock(progress->mutex) != 0) {
-    dmnsn_error(DMNSN_SEVERITY_MEDIUM, "Couldn't lock condition mutex.");
-  }
-
-  while (dmnsn_get_progress(progress) < prog) {
-    if (pthread_cond_wait(progress->cond, progress->mutex) != 0) {
-      dmnsn_error(DMNSN_SEVERITY_MEDIUM,
-                  "Couldn't wait on condition variable.");
+    dmnsn_error(DMNSN_SEVERITY_LOW, "Couldn't lock condition mutex.");
+  } else {
+    while (dmnsn_get_progress(progress) < prog) {
+      if (pthread_cond_wait(progress->cond, progress->mutex) != 0) {
+        dmnsn_error(DMNSN_SEVERITY_LOW,
+                    "Couldn't wait on condition variable.");
+      }
     }
-  }
 
-  if (pthread_mutex_unlock(progress->mutex) != 0) {
-    dmnsn_error(DMNSN_SEVERITY_MEDIUM, "Couldn't unlock condition mutex.");
+    if (pthread_mutex_unlock(progress->mutex) != 0) {
+      dmnsn_error(DMNSN_SEVERITY_LOW, "Couldn't unlock condition mutex.");
+    }
   }
 }
 
-/* A new level of algorithmic nesting */
+/* Start a new level of algorithmic nesting */
 void
 dmnsn_new_progress_element(dmnsn_progress *progress, unsigned int total)
 {
@@ -173,13 +175,14 @@ dmnsn_increment_progress(dmnsn_progress *progress)
   dmnsn_array_wrlock(progress->elements);
     size = dmnsn_array_size_unlocked(progress->elements);
     element = dmnsn_array_at(progress->elements, size - 1);
-    ++element->progress;
+    ++element->progress; /* Increment the last element */
 
     while (element->progress >= element->total && size > 1) {
+      /* As long as the last element is complete, pop it */
       --size;
       dmnsn_array_resize_unlocked(progress->elements, size);
       element = dmnsn_array_at(progress->elements, size - 1);
-      ++element->progress;
+      ++element->progress; /* Increment the next element */
     }
 
     if (pthread_cond_broadcast(progress->cond) != 0) {
@@ -190,7 +193,7 @@ dmnsn_increment_progress(dmnsn_progress *progress)
 
 /* Immediately set to 100% completion */
 void
-dmnsn_progress_done(dmnsn_progress *progress)
+dmnsn_done_progress(dmnsn_progress *progress)
 {
   dmnsn_progress_element *element;
 
diff --git a/libdimension/raytrace.c b/libdimension/raytrace.c
index bd423c2..aa3a445 100644
--- a/libdimension/raytrace.c
+++ b/libdimension/raytrace.c
@@ -21,13 +21,17 @@
 #include "dimension.h"
 #include <unistd.h> /* For sysconf */
 
+/* Payload type for passing arguments to worker thread */
+
 typedef struct {
   dmnsn_progress *progress;
   dmnsn_scene *scene;
 } dmnsn_raytrace_payload;
 
+/* Thread callback */
 static void *dmnsn_raytrace_scene_thread(void *ptr);
 
+/* Raytrace a scene */
 void
 dmnsn_raytrace_scene(dmnsn_scene *scene)
 {
@@ -35,6 +39,7 @@ dmnsn_raytrace_scene(dmnsn_scene *scene)
   dmnsn_finish_progress(progress);
 }
 
+/* Raytrace a scene in the background */
 dmnsn_progress *
 dmnsn_raytrace_scene_async(dmnsn_scene *scene)
 {
@@ -54,8 +59,7 @@ dmnsn_raytrace_scene_async(dmnsn_scene *scene)
     if (pthread_create(&progress->thread, NULL, &dmnsn_raytrace_scene_thread,
                        payload)
         != 0) {
-      dmnsn_error(DMNSN_SEVERITY_MEDIUM,
-                  "Creating raytracing worker thread failed.");
+      free(payload);
       dmnsn_delete_progress(progress);
       return NULL;
     }
@@ -64,9 +68,11 @@ dmnsn_raytrace_scene_async(dmnsn_scene *scene)
   return progress;
 }
 
+/* Actual raytracing implementation */
 static void dmnsn_raytrace_scene_impl(dmnsn_progress *progress,
                                       dmnsn_scene *scene);
 
+/* Thread callback */
 static void *
 dmnsn_raytrace_scene_thread(void *ptr)
 {
@@ -76,7 +82,8 @@ dmnsn_raytrace_scene_thread(void *ptr)
     dmnsn_raytrace_scene_impl(payload->progress, payload->scene);
     *retval = 0;
   }
-  dmnsn_progress_done(payload->progress);
+  dmnsn_done_progress(payload->progress);
+  free(payload);
   return retval;
 }
 
@@ -116,6 +123,7 @@ dmnsn_raytrace_scene_impl(dmnsn_progress *progress, dmnsn_scene *scene)
 
         /* Test for intersections with objects */
         intersections = (*object->intersections_fn)(object, ray_trans);
+        /* Find the closest intersection */
         for (l = 0; l < dmnsn_array_size(intersections); ++l) {
           dmnsn_array_get(intersections, l, &t_temp);
           if (t_temp < t || t == 0.0) t = t_temp;
@@ -123,6 +131,7 @@ dmnsn_raytrace_scene_impl(dmnsn_progress *progress, dmnsn_scene *scene)
         dmnsn_delete_array(intersections);
       }
 
+      /* Shade according to distance from camera */
       if (t != 0.0) {
         sRGB.R = 1.0 - (t - 2.25)/2.25;
         sRGB.G = sRGB.R;
diff --git a/libdimension/scene.c b/libdimension/scene.c
index 048ad45..9405f03 100644
--- a/libdimension/scene.c
+++ b/libdimension/scene.c
@@ -21,6 +21,7 @@
 #include "dimension.h"
 #include <stdlib.h> /* For malloc */
 
+/* Allocate an empty scene */
 dmnsn_scene *
 dmnsn_new_scene()
 {
@@ -30,6 +31,7 @@ dmnsn_new_scene()
   return scene;
 }
 
+/* Free a scene */
 void
 dmnsn_delete_scene(dmnsn_scene *scene)
 {
diff --git a/libdimension/sphere.c b/libdimension/sphere.c
index 5a4d1a9..f6950dc 100644
--- a/libdimension/sphere.c
+++ b/libdimension/sphere.c
@@ -22,11 +22,13 @@
 #include <stdlib.h> /* For malloc */
 #include <math.h>   /* For sqrt   */
 
+/* Sphere object callbacks */
 static dmnsn_array *dmnsn_sphere_intersections_fn(const dmnsn_object *sphere,
                                                   dmnsn_line line);
 static int dmnsn_sphere_inside_fn(const dmnsn_object *sphere,
                                   dmnsn_vector point);
 
+/* Allocate a new sphere */
 dmnsn_object *
 dmnsn_new_sphere()
 {
@@ -38,12 +40,14 @@ dmnsn_new_sphere()
   return sphere;
 }
 
+/* Free a sphere */
 void
 dmnsn_delete_sphere(dmnsn_object *sphere)
 {
   dmnsn_delete_object(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)
 {
@@ -66,8 +70,9 @@ dmnsn_sphere_intersections_fn(const dmnsn_object *sphere, dmnsn_line line)
   return array;
 }
 
+/* Return whether a point is inside a sphere (x**2 + y**2 + z**2 < 1.0) */
 static int
 dmnsn_sphere_inside_fn(const dmnsn_object *sphere, dmnsn_vector point)
 {
-  return sqrt(point.x*point.x + point.y*point.y + point.z*point.z) < 1.0;
+  return point.x*point.x + point.y*point.y + point.z*point.z < 1.0;
 }