[Pkg-javascript-commits] [pdf.js] 35/157: Zoom relative to cursor position via mouse wheel

[David Prévot]

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taffit pushed a commit to branch master
in repository pdf.js.

commit 2932f7c6761fc523087c0d514b93488eb92e7236
Author: Rob Wu <rob at robwu.nl>
Date:   Thu Jul 2 23:20:37 2015 +0200

    Zoom relative to cursor position via mouse wheel
    
    Before this patch, zooming in/out via the scroll wheel caused the page
    to be zoomed relative to the upper-left corner of the page, i.e. the
    upper-left corner of the page stays at a fixed position.
    
    After this patch, the page is zoomed relative to the cursor position,
    i.e. after zooming in/out, the part under the cursor 'has not moved'.
    
    This only applies when the page does not fit in the viewport, because
    pages smaller than the viewpoer are always centered.
---
 web/viewer.js | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/web/viewer.js b/web/viewer.js
index 1588ad6..c42545f 100644
--- a/web/viewer.js
+++ b/web/viewer.js
@@ -1811,14 +1811,31 @@ function handleMouseWheel(evt) {
               evt.wheelDelta / MOUSE_WHEEL_DELTA_FACTOR;
   var direction = (ticks < 0) ? 'zoomOut' : 'zoomIn';
 
-  if (PDFViewerApplication.pdfViewer.isInPresentationMode) {
+  var pdfViewer = PDFViewerApplication.pdfViewer;
+  if (pdfViewer.isInPresentationMode) {
     evt.preventDefault();
     PDFViewerApplication.scrollPresentationMode(ticks *
                                                 MOUSE_WHEEL_DELTA_FACTOR);
   } else if (evt.ctrlKey || evt.metaKey) {
     // Only zoom the pages, not the entire viewer.
     evt.preventDefault();
+
+    var previousScale = pdfViewer.currentScale;
+
     PDFViewerApplication[direction](Math.abs(ticks));
+
+    var currentScale = pdfViewer.currentScale;
+    if (previousScale !== currentScale) {
+      // After scaling the page via zoomIn/zoomOut, the position of the upper-
+      // left corner is restored. When the mouse wheel is used, the position
+      // under the cursor should be restored instead.
+      var scaleCorrectionFactor = currentScale / previousScale - 1;
+      var rect = pdfViewer.container.getBoundingClientRect();
+      var dx = evt.clientX - rect.left;
+      var dy = evt.clientY - rect.top;
+      pdfViewer.container.scrollLeft += dx * scaleCorrectionFactor;
+      pdfViewer.container.scrollTop += dy * scaleCorrectionFactor;
+    }
   }
 }
 

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