[refactor] point containment, generalized [add] intersections

1 files changed, 28 insertions, 1 deletions

diff --git a/src/utils.lisp b/src/utils.lisp
index 7024a8d..165f29a 100644
--- a/src/utils.lisp
+++ b/src/utils.lisp
@@ -25,7 +25,7 @@ order, nil if not."
         (- (vec:vx c) (vec:vx a)))))
 
 
-(defun intersectp (a b c d)
+(defun segments-intersect-p (a b c d)
   "A B C and D are vectors of the sort created by 3d-vectors:vec,
 each representing a 2d point.  Returns T if the line segment between A
 and B intersects the linesegment between C and D, NIL otherwise."
@@ -33,6 +33,33 @@ and B intersects the linesegment between C and D, NIL otherwise."
       (and (not (eq (counterclockwisep a c d) (counterclockwisep b c d)))
            (not (eq (counterclockwisep a b c) (counterclockwisep a b d))))))
 
+(defun paths-intersect-p (path-a path-b)
+  "Paths are lists of vectors, each of which represents a 2d point."
+  (loop for (a1 a2 . more-a) on path-a
+        while a2
+          thereis (loop for (b1 b2 . b-more) on path-b
+                        while b2
+                          thereis (segments-intersect-p a1 a2 b1 b2))))
+
+(defun path-contains-point (path pt)
+  "Path is a list of vectors, pt is a single vector."
+  (let* ((bounds
+           (path-bounds path))
+         (corner
+           ;; creating a point guaranteed to be outside of the path
+           (vec:vec (- (getf bounds :left) (getf bounds :width))
+                    (- (getf bounds :bottom) (getf bounds :height))
+                    0.0 1.0)))
+    (loop for (p1 p2 . more) on path
+          while p2
+          when (segments-intersect-p p1 p2 pt corner)
+            count 1 into intersection-count
+          finally
+             (return (oddp intersection-count)))))
+
+(defun path-encloses-p (path other)
+  )
+
 (defun path-bounds (path)
   "Path is a list of vectors representing 2d points. Returns the
 bounds and width and height as a plist of the form