fix onDifferentSides

sirius.cpp

@@ -204,13 +204,12 @@ inline float cross(vec2 a, vec2 b) {
 
 inline bool onDifferentSides(vec2 p1, vec2 p2, vec2 q1, vec2 q2) {
     vec2 v = p2 - p1;
-  vec2 r = p1;
-  return cross(v, p1 - r) * cross(v, p2 - r) < 0;
+    return cross(v, q1 - p1) * cross(v, q2 - p1) < 0;
 }
 
 inline bool intersectEachOther(vec2 p1, vec2 p2, vec2 q1, vec2 q2) {
-  return
-    onDifferentSides(p1, p2, q1, q2) && onDifferentSides(q1, q2, p1, p2);
+    return onDifferentSides(p1, p2, q1, q2) &&
+           onDifferentSides(q1, q2, p1, p2);
 }
 
 class Triangulated : public Drawable {