1 files changed, 51 insertions, 0 deletions
diff --git a/ray.c b/ray.c
new file mode 100644
index 0000000..d2b15cc
--- /dev/null
+++ b/ray.c
@@ -0,0 +1,51 @@
+#include <math.h>
+#include "vector.h"
+
+#include "ray.h"
+
+// https://en.wikipedia.org/wiki/Line%E2%80%93sphere_intersection
+// http://viclw17.github.io/2018/07/16/raytracing-ray-sphere-intersection/
+COORD_T ray_intersect_sphere(sphere_t *s, ray_t *ray)
+{
+    // Vector between vector start and center of circle
+    vector_t oc;
+    vector_sub(&oc, ray->start, s->center);
+
+    // Solve quadratic function
+	// TODO Not sure if this step i neccesary because dir is unit
+    COORD_T a = vector_dot(&ray->direction, &ray->direction);
+    COORD_T b = 2 * vector_dot(&oc, &ray->direction);
+    COORD_T c = vector_dot(&oc, &oc) - s->radius * s->radius;
+
+    COORD_T d = b * b - 4 * a * c;
+
+    // no intersection
+    if (d < 0) {
+        return -1;
+    }
+
+    // Else take the closest intersection
+    return (-b - sqrt(d) ) / (2.0 * a);
+}
+
+// Requires that vectors are normalized
+// https://www.scratchapixel.com/lessons/3d-basic-rendering/minimal-ray-tracer-rendering-simple-shapes/ray-plane-and-ray-disk-intersection
+COORD_T ray_intersect_plane(plane_t *p, ray_t *ray)
+{
+	// If zero ray is parralel to plane
+	COORD_T nr = vector_dot(&p->norm, &ray->direction);
+	vector_print(&ray->direction);
+	//
+	// Take care of rounding errors
+	if (nr < ZERO_APROX && nr > -ZERO_APROX) {
+		return -1;
+	}
+
+	// Calculate distance
+	vector_t tmp;
+	vector_copy(&tmp, p->start);
+	vector_sub(&tmp, &tmp, ray->start);
+
+	COORD_T t = vector_dot(&tmp, &p->norm) / nr;
+	return t;
+}