From 25e4eece171cd056cb2d8d47f07403551975c41a Mon Sep 17 00:00:00 2001
From: Kamil Bielawski <k_bielawski@fastmail.fm>
Date: Wed, 30 Aug 2017 00:17:24 +0200
Subject: [PATCH] Allow specifying bounding box for comparison

---
 resemble.js | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/resemble.js b/resemble.js
index 78d4e12..6952ecc 100644
--- a/resemble.js
+++ b/resemble.js
@@ -29,6 +29,17 @@ URL: https://github.com/Huddle/Resemble.js
 		return (Math.abs(c1.r - c2.r) + Math.abs(c1.g - c2.g) + Math.abs(c1.b - c2.b))/3;
 	}
 
+	function withinBoundingBox(x, y) {
+		if (boundingBox === null) {
+			return true;
+    }
+
+    return x > boundingBox.x1 &&
+      x < boundingBox.x2 &&
+      y > boundingBox.y1 &&
+      y < boundingBox.y2;
+  }
+
 	var errorPixelTransform = {
 		flat: function (px, offset, d1, d2) {
 			px[offset] = errorPixelColor.red;
@@ -59,6 +70,7 @@ URL: https://github.com/Huddle/Resemble.js
 	};
 
 	var errorPixel = errorPixelTransform.flat;
+	var boundingBox = null;
 	var largeImageThreshold = 1200;
 	var useCrossOrigin = true;
 	var document = typeof window != "undefined" ? window.document : {};
@@ -421,6 +433,7 @@ URL: https://github.com/Huddle/Resemble.js
 				}
 
 				var offset = (verticalPos*width + horizontalPos) * 4;
+				var isWithinBoundingBox = withinBoundingBox(horizontalPos, verticalPos);
 
 				if (!getPixelInfo(pixel1, data1, offset, 1) || !getPixelInfo(pixel2, data2, offset, 2)) {
 					return;
@@ -431,7 +444,7 @@ URL: https://github.com/Huddle/Resemble.js
 					addBrightnessInfo(pixel1);
 					addBrightnessInfo(pixel2);
 
-					if( isPixelBrightnessSimilar(pixel1, pixel2) ){
+					if( isPixelBrightnessSimilar(pixel1, pixel2) || !isWithinBoundingBox ){
 						copyGrayScalePixel(targetPix, offset, pixel2);
 					} else {
 						errorPixel(targetPix, offset, pixel1, pixel2);
@@ -441,7 +454,7 @@ URL: https://github.com/Huddle/Resemble.js
 					return;
 				}
 
-				if( isRGBSimilar(pixel1, pixel2) ){
+				if( isRGBSimilar(pixel1, pixel2)  || !isWithinBoundingBox ){
 					copyPixel(targetPix, offset, pixel1, pixel2);
 
 				} else if( ignoreAntialiasing && (
@@ -451,7 +464,7 @@ URL: https://github.com/Huddle/Resemble.js
 						isAntialiased(pixel2, data2, 2, verticalPos, horizontalPos, width)
 					)){
 
-					if( isPixelBrightnessSimilar(pixel1, pixel2) ){
+					if( isPixelBrightnessSimilar(pixel1, pixel2) || !isWithinBoundingBox ){
 						copyGrayScalePixel(targetPix, offset, pixel2);
 					} else {
 						errorPixel(targetPix, offset, pixel1, pixel2);
@@ -704,6 +717,10 @@ URL: https://github.com/Huddle/Resemble.js
 			useCrossOrigin = options.useCrossOrigin;
 		}
 
+		if (options.boundingBox !== undefined) {
+			boundingBox = options.boundingBox;
+		}
+
 		return this;
 	};