1 files changed, 48 insertions, 0 deletions
diff --git a/src/utils.lisp b/src/utils.lisp
index 3598ec3..7024a8d 100644
--- a/src/utils.lisp
+++ b/src/utils.lisp
@@ -14,3 +14,51 @@
                     (slot-value object slot)))
     val
     default))
+
+(defun counterclockwisep (a b c)
+  "A B and C are vectors created by 3d-vectors:vec, each representing
+a 2d point.  Returns T if the three are supplied in counterclockwise
+order, nil if not."
+  (> (* (- (vec:vx b) (vec:vx a))
+        (- (vec:vy c) (vec:vy a)))
+     (* (- (vec:vy b) (vec:vy a))
+        (- (vec:vx c) (vec:vx a)))))
+
+
+(defun intersectp (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."
+  (or (vec:v= a c) (vec:v= a d) (vec:v= b c) (vec:v= b d)
+      (and (not (eq (counterclockwisep a c d) (counterclockwisep b c d)))
+           (not (eq (counterclockwisep a b c) (counterclockwisep a b d))))))
+
+(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 
+
+(:top N :left N :right N :bottom N :width N :height N)
+
+This is the smallest UNROTATED RECTANGLE that contains the points in
+the path."
+  (loop
+    with max-x = nil
+    and max-y = nil
+    and min-x = nil
+    and min-y = nil
+    for vec in path
+    for x = (vec:vx vec)
+    for y = (vec:vy vec)
+    when (or (null max-x) (< max-x x))
+      do (setf max-x x)
+    when (or (null min-x) (< x min-x))
+      do (setf min-x x)
+    when (or (null max-y) (< max-y y))
+      do (setf max-y y)
+    when (or (null min-y) (< y min-y))
+      do (setf min-y y)
+    finally
+       (return (list :top max-y :left min-x :right max-x :bottom min-y
+                     :width (- max-x min-x)
+                     :height (- max-y min-y)))))
+