1 files changed, 58 insertions, 0 deletions
diff --git a/viewpoint.ino b/viewpoint.ino
new file mode 100644
index 0000000..62ff08a
--- /dev/null
+++ b/viewpoint.ino
@@ -0,0 +1,58 @@
+#include "viewpoint.h"
+
+#include <stdio.h>
+#include <math.h>
+#include <stdlib.h>
+
+static const vector_t up = {0, 0, 1};
+
+void viewpoint_init(viewpoint_t *view)
+{
+	// Vector from E to T
+	vector_t t;
+	vector_sub(&t, &view->target, &view->position);
+
+	// Calculate orthogonal vectors to E
+	vector_t b, v;
+	vector_cross(&b, (vector_t *)&up, &t);
+
+	// Convert to unit-vectors
+	vector_scale_inv(&t, &t, vector_len(&t));
+	vector_scale_inv(&b, &b, vector_len(&b));
+
+	vector_cross(&v, &t, &b);
+
+	// Calculate size of viewplane
+	COORD_T gx = tanf( FOV / 2 );
+	COORD_T gy = gx * ((COORD_T)view->height / view->width);
+
+	// Calculate viewplane vectors
+	vector_scale(&view->qx, &b, ( 2 * gx ) / (view->width - 1));
+	vector_scale(&view->qy, &v, ( 2 * gy ) / (view->height - 1));
+	
+	// Viewplane starting point
+	vector_copy(&view->blc, &t);
+	// This will thrash b and v
+	vector_sub(&view->blc, &view->blc, vector_scale(&b, &b, gx));
+	vector_sub(&view->blc, &view->blc, vector_scale(&v, &v, gy));
+
+}
+
+// Calculate ray for viewport w, h
+// https://en.wikipedia.org/wiki/Ray_tracing_(graphics)
+void viewpoint_ray(viewpoint_t *view, vector_t *r, COORD_T x, COORD_T y)
+{
+	// Calculate ray vector
+	vector_copy(r, &view->blc);
+
+	vector_t t;
+	vector_scale(&t, &view->qx, x);
+	vector_add(r, r, &t);
+
+	vector_scale(&t, &view->qy,	y);
+	vector_add(r, r, &t);
+
+	// Calculate unit vector
+	vector_scale_inv(r, r, vector_len(r));
+}
+