special case of polygon for rectangles

Author: alexcjohnson

src/lib/polygon.js

@@ -14,7 +14,7 @@ var dot = require('./matrix').dot;
  * Turn an array of [x, y] pairs into a polygon object
  * that can test if points are inside it
  *
- * @param pts Array of [x, y] pairs
+ * @param ptsIn Array of [x, y] pairs
  *
  * @returns polygon Object {xmin, xmax, ymin, ymax, pts, contains}
  *      (x|y)(min|max) are the bounding rect of the polygon
@@ -43,6 +43,47 @@ polygon.tester = function tester(ptsIn) {
         ymax = Math.max(ymax, pts[i][1]);
     }
 
+    // do we have a rectangle? Handle this here, so we can use the same
+    // tester for the rectangular case without sacrificing speed
+
+    var isRect = false,
+        rectFirstEdgeTest;
+
+    function onFirstVert(pt) { return pt[0] === pts[0][0]; }
+    function onFirstHorz(pt) { return pt[1] === pts[0][1]; }
+
+    if(pts.length === 5) {
+        if(pts[0][0] === pts[1][0]) { // vert, horz, vert, horz
+            if(pts[2][0] === pts[3][0] &&
+                    pts[0][1] === pts[3][1] &&
+                    pts[1][1] === pts[2][1]) {
+                isRect = true;
+                rectFirstEdgeTest = onFirstVert;
+            }
+        }
+        else if(pts[0][1] === pts[1][1]) { // horz, vert, horz, vert
+            if(pts[2][1] === pts[3][1] &&
+                    pts[0][0] === pts[3][0] &&
+                    pts[1][0] === pts[2][0]) {
+                isRect = true;
+                rectFirstEdgeTest = onFirstHorz;
+            }
+        }
+    }
+
+    function rectContains(pt, omitFirstEdge) {
+        var x = pt[0],
+            y = pt[1];
+
+        if(x < xmin || x > xmax || y < ymin || y > ymax) {
+            // pt is outside the bounding box of polygon
+            return false;
+        }
+        if(omitFirstEdge && rectFirstEdgeTest(pt)) return false;
+
+        return true;
+    }
+
     function contains(pt, omitFirstEdge) {
         var x = pt[0],
             y = pt[1];
@@ -115,7 +156,8 @@ polygon.tester = function tester(ptsIn) {
         ymin: ymin,
         ymax: ymax,
         pts: pts,
-        contains: contains
+        contains: isRect ? rectContains : contains,
+        isRect: isRect
     };
 };
 

test/jasmine/tests/polygon_test.js

@@ -64,10 +64,8 @@ describe('polygon.tester', function() {
     });
 
     it('should prepare a polygon object correctly', function() {
-        var polyPts = [
-            [[0, 0], [0, 1], [1, 1], [1, 0]],
-            [[-2.34, -0.67], [0.12345, 1.2345], [1.3456, 1.4567], [1.5678, 0.21345]]
-        ];
+        var polyPts = [squareCW, squareCCW, bowtie, squareish, equilateralTriangle,
+            zigzag, donut, donut2];
 
         polyPts.forEach(function(polyPt) {
             var poly = polygonTester(polyPt),
@@ -93,6 +91,12 @@ describe('polygon.tester', function() {
 
         polyPts.forEach(function(polyPt) {
             var poly = polygonTester(polyPt);
+
+            var isRect = polyPt === squareCW || polyPt === squareCCW;
+            expect(poly.isRect).toBe(isRect);
+            // to make sure we're only using the bounds and first pt, delete the rest
+            if(isRect) poly.pts.splice(1, poly.pts.length);
+
             poly.pts.forEach(function(pt1, i) {
                 if(!i) return;
                 var pt0 = poly.pts[i - 1],