1 files changed, 85 insertions, 0 deletions
diff --git a/src/modules/ray/ray_camera.c b/src/modules/ray/ray_camera.c
new file mode 100644
index 0000000..0703c2e
--- /dev/null
+++ b/src/modules/ray/ray_camera.c
@@ -0,0 +1,85 @@
+#include "fb.h"
+
+#include "ray_camera.h"
+#include "ray_euler.h"
+
+
+/* Produce a vector from the provided orientation vectors and proportions. */
+static ray_3f_t project_corner(ray_3f_t *forward, ray_3f_t *left, ray_3f_t *up, float focal_length, float horiz, float vert)
+{
+	ray_3f_t	tmp;
+	ray_3f_t	corner;
+
+	corner = ray_3f_mult_scalar(forward, focal_length);
+	tmp = ray_3f_mult_scalar(left, horiz);
+	corner = ray_3f_add(&corner, &tmp);
+	tmp = ray_3f_mult_scalar(up, vert);
+	corner = ray_3f_add(&corner, &tmp);
+
+	return ray_3f_normalize(&corner);
+}
+
+
+/* Produce vectors for the corners of the entire camera frame, used for interpolation. */
+static void project_corners(ray_camera_t *camera, ray_camera_frame_t *frame)
+{
+	ray_3f_t	forward, left, up, right, down;
+	float		half_horiz = (float)camera->width / 2.0f;
+	float		half_vert = (float)camera->height / 2.0f;
+
+	ray_euler_basis(&camera->orientation, &forward, &up, &left);
+	right = ray_3f_negate(&left);
+	down = ray_3f_negate(&up);
+
+	frame->nw = project_corner(&forward, &left, &up, camera->focal_length, half_horiz,  half_vert);
+	frame->ne = project_corner(&forward, &right, &up, camera->focal_length, half_horiz,  half_vert);
+	frame->se = project_corner(&forward, &right, &down, camera->focal_length, half_horiz,  half_vert);
+	frame->sw = project_corner(&forward, &left, &down, camera->focal_length, half_horiz,  half_vert);
+}
+
+
+/* Begin a frame for the fragment of camera projection, initializing frame and ray. */
+void ray_camera_frame_begin(ray_camera_t *camera, fb_fragment_t *fragment, ray_ray_t *ray, ray_camera_frame_t *frame)
+{
+	/* References are kept to the camera, fragment, and ray to be traced.
+	 * The ray is maintained as we step through the frame, that is the
+	 * purpose of this api.
+	 *
+	 * Since the ray direction should be a normalized vector, the obvious
+	 * implementation is a bit costly.  The camera frame api hides this
+	 * detail so we can explore interpolation techniques to potentially
+	 * lessen the per-pixel cost.
+	 */
+	frame->camera = camera;
+	frame->fragment = fragment;
+	frame->ray = ray;
+
+	frame->x = frame->y = 0;
+
+	/* From camera->orientation and camera->focal_length compute the vectors
+	 * through the viewport's corners, and place these normalized vectors
+	 * in frame->(nw,ne,sw,se).
+	 *
+	 * These can than be interpolated between to produce the ray vectors
+	 * throughout the frame's fragment.  The efficient option of linear
+	 * interpolation will not maintain the unit vector length, so to
+	 * produce normalized interpolated directions will require the costly
+	 * normalize function.
+	 *
+	 * I'm hoping a simple length correction table can be used to fixup the
+	 * linearly interpolated vectors to make them unit vectors with just
+	 * scalar multiplication instead of the sqrt of normalize.
+	 */
+	project_corners(camera, frame);
+
+	frame->x_delta = 1.0f / (float)camera->width;
+	frame->y_delta = 1.0f / (float)camera->height;
+	frame->x_alpha = frame->x_delta * (float)fragment->x;
+	frame->y_alpha = frame->y_delta * (float)fragment->y;
+
+	frame->cur_w = ray_3f_nlerp(&frame->nw, &frame->sw, frame->y_alpha);
+	frame->cur_e = ray_3f_nlerp(&frame->ne, &frame->se, frame->y_alpha);
+
+	ray->origin = camera->position;
+	ray->direction = frame->cur_w;
+}