After upgrading mupdf from version 1.1 to 1.2, I noticed that scrolling and panning across a document using the mouse is significantly slower. It sometimes takes upwards of 10 seconds for the document to completely scroll to the desired position. Interestingly, the issue is worse if I click and drag the mouse at a slower speed.

Resizing the mupdf window suffers from a similar lag. It takes much longer for the document to be recentered in the window as compared to version 1.1.

Keyboard scrolling in mupdf using the hjkl keys appears unaffected.

Additional info:

Affects mupdf version 1.2

Steps to reproduce:

1. Open a PDF document.
2. Zoom in to a relatively high DPI by pressing the '+' key.
3. Using the mouse, press and hold the left click button and slowly drag the mouse to pan and scroll the document. The document scrolls very slowly and it can take upwards of several second for the document to fully scroll into position.

This issue has been fixed upstream.
See: http://bugs.ghostscript.com/show_bug.cgi?id=693679

I applied the upstream fix to version 1.2, tested it, and it solved the problem. See attached for the patch.