gopprof: fix bug: do not rotate 180 degrees for large scrolls

R=r
CC=golang-dev
https://golang.org/cl/4273088

diff --git a/src/cmd/prof/gopprof b/src/cmd/prof/gopprof
index c7b242dec7573011ebc90de15e51dd86a28c340d..e391f36a0b4f74b70b80b5dcab2fe23fef8957ee 100755 (executable)
--- a/src/cmd/prof/gopprof
+++ b/src/cmd/prof/gopprof
@@ -1896,6 +1896,7 @@ sub SvgJavascript {
 // SVGPan
 // http://www.cyberz.org/blog/2009/12/08/svgpan-a-javascript-svg-panzoomdrag-library/
 // Local modification: if(true || ...) below to force panning, never moving.
+// Local modification: add clamping to fix bug in handleMouseWheel.
 
 /**
  *  SVGPan library 1.2
@@ -2038,6 +2039,15 @@ function handleMouseWheel(evt) {
 
        var z = 1 + delta; // Zoom factor: 0.9/1.1
 
+       // Clamp to reasonable values.
+       // The 0.1 check is important because
+       // a very large scroll can turn into a
+       // negative z, which rotates the image 180 degrees.
+       if(z < 0.1)
+               z = 0.1;
+       if(z > 10.0)
+               z = 10.0;
+               
        var g = svgDoc.getElementById("viewport");
 
        var p = getEventPoint(evt);