Add rudimentary collision detection

collisions.cpp

@@ -0,0 +1,48 @@
+#include <glm/glm.hpp>
+
+float abs(float x) {
+    if (x < 0) {
+        return -x;
+    }
+    return x;
+}
+
+int signbit(float x) {
+    if (x < 0) {
+        return 1;
+    }
+    return 0;
+}
+
+int getIntersection(glm::vec3 vec_start, glm::vec3 vec_stop, glm::vec3 P1, glm::vec3 P2, glm::vec3 P3) {
+
+    glm::vec3 lba = vec_start - vec_stop;
+    glm::vec3 v01 = P2 - P1;
+    glm::vec3 v02 = P3 - P1;
+    glm::vec3 cross12 = glm::cross(v01, v02);
+    float det = glm::dot(lba, cross12);
+    if (abs(det) < 0.0000001) {
+        return 0;
+    }
+
+    glm::vec3 diff_start = vec_start - P1;
+    float tn = glm::dot(cross12, diff_start);
+    if (signbit(tn) != signbit(det) || abs(det) < abs(tn)) {
+        return 0;
+    }
+
+    glm::vec3 coefU = glm::cross(v02, lba);
+    float un = glm::dot(coefU, diff_start);
+    if (signbit(un) != signbit(det) || abs(det) < abs(un)) {
+        return 0;
+    }
+
+    glm::vec3 coefV = glm::cross(lba, v01);
+    float vn = glm::dot(coefV, diff_start);
+    if (signbit(vn) != signbit(det) || abs(det) < abs(vn)) {
+        return 0;
+    }
+
+    return 1;
+
+}