Closed Bug 402843 Opened 15 years ago Closed 15 years ago

full page zoom of an image to off-screen, scroll, the image breaks apart


(Core :: Web Painting, defect, P2)






(Reporter: Aleksej, Assigned: roc)





(2 files)

Mozilla/5.0 (X11; U; Linux i686 (x86_64); en-US; rv:1.9a9pre) Gecko/2007110604 Minefield/3.0a9pre

Steps to reproduce:
1. Load the URL, or any other page with an image sufficiently large for step 3. In this case, the image fits in the browser at first.
2. Scroll down a bit, so the image is near the top of the browser.
3. Zoom in (“Ctrl-+” or menu) until a part of the image is out of sight.
4. Scroll right (“→” or scrollbar)

The image breaks into pieces — some go down (e.g., the part that was out of screen), and some go up.

Can probably be reproduced on any image — including the tab bar (Products | Support | Store …) at

Also seen by mw22 on a Windows* build.
Flags: blocking1.9?
Whiteboard: DUPEME?
Attachment #287674 - Attachment description: A screenshot of the problem at Minefield’s home page. {the page is cc by-sa 2.0} → A screenshot of the problem at Minefield’s home page. {the page text is cc by-sa 2.0}
Blocks: pagezoom
No longer blocks: 389628
Flags: blocking1.9? → blocking1.9+
Priority: -- → P2
What seems to be happening here is that when we zoom, the nominal scroll position stays constant in device pixels, but everything draws as if it had stayed constant in CSS pixels. Then when you scroll we suddenly realize that the scrolled offset is in device pixels and things get screwy.

So basically it looks like scroll positions get out of sync, probably the frame position stays constant in CSS-pixels/appunits and the view position (or the scrollbar position>) stays constant in device pixels.
Attached patch fixSplinter Review
This is quite simple actually. nsScrollPortView has fields mOffsetXpx and mOffsetYpy, which are basically mOffsetX and mOffsetY in device pixels. Problem is, when we change the appunits-to-dev-pixels ratio, mOffsetXpx and mOffsetYpy get out of sync... The solution is simple, don't store them persistently in the first place.
Attachment #288630 - Flags: superreview?(bzbarsky)
Attachment #288630 - Flags: review?(bzbarsky)
Whiteboard: DUPEME? → [needs review]
Comment on attachment 288630 [details] [diff] [review]

Makes sense
Attachment #288630 - Flags: superreview?(bzbarsky)
Attachment #288630 - Flags: superreview+
Attachment #288630 - Flags: review?(bzbarsky)
Attachment #288630 - Flags: review+
checked in
Closed: 15 years ago
Resolution: --- → FIXED
Verified fixed on GNU/Linux with
Mozilla/5.0 (X11; U; Linux i686 (x86_64); en-US; rv:1.9b2pre) Gecko/2007111704 Minefield/3.0b2pre
Whiteboard: [needs review]
Component: Layout: View Rendering → Layout: Web Painting
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