From: Evert Timberg <evert.timberg@gmail.com>
Date: Sun, 20 Sep 2015 21:57:27 +0000 (-0400)
Subject: Convert screen coordinates into canvas coordinates when dealing with mouse events
X-Git-Tag: 2.0.0-alpha4~20^2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=refs%2Fpull%2F1471%2Fhead;p=thirdparty%2FChart.js.git

Convert screen coordinates into canvas coordinates when dealing with mouse events
---

diff --git a/src/core/core.helpers.js b/src/core/core.helpers.js
index ab58b0789..bd18fd08d 100644
--- a/src/core/core.helpers.js
+++ b/src/core/core.helpers.js
@@ -642,14 +642,20 @@
 				boundingRect = canvas.getBoundingClientRect();
 
 			if (e.touches) {
-				mouseX = e.touches[0].clientX - boundingRect.left;
-				mouseY = e.touches[0].clientY - boundingRect.top;
+				mouseX = e.touches[0].clientX;
+				mouseY = e.touches[0].clientY;
 
 			} else {
-				mouseX = e.clientX - boundingRect.left;
-				mouseY = e.clientY - boundingRect.top;
+				mouseX = e.clientX;
+				mouseY = e.clientY;
 			}
 
+			// Scale mouse coordinates into canvas coordinates
+			// by following the pattern laid out by 'jerryj' in the comments of 
+			// http://www.html5canvastutorials.com/advanced/html5-canvas-mouse-coordinates/
+			mouseX = Math.round((mouseX - boundingRect.left) / (boundingRect.right - boundingRect.left) * canvas.width);
+			mouseY = Math.round((mouseY - boundingRect.top) / (boundingRect.bottom - boundingRect.top) * canvas.height);
+
 			return {
 				x: mouseX,
 				y: mouseY