Public bug reported:
In PikoPixel 1.0 BETA9b (current Bionic version), resizing an image
window to within a few pixels of the canvas size can cause the app to
freeze, eventually crashing due to a stack overflow.
A bugfix update, 1.0 BETA9c, fixes the issue, and is now in the
Cosmic repo. Updating Bionic to Cosmic's version would prevent users
from losing unsaved image data due to this issue.
The crash is the result of a bug in PikoPixel's scrollview-layout
code that causes an infinite-recursion loop of hiding & showing the
scrollers: Window is resized -> Scrollview layout is updated -> New
layout causes scrollers to become visible -> Scroller-visibility change
causes re-layout of scrollview -> New layout causes scrollers to hide ->
Scroller-visibility change causes re-layout of scrollview -> New layout
causes scrollers to show -> etc.
[Test Case]
1) Start the PikoPixel app.
2) On the "New Image" panel, click the "OK" button to create a new image (64x64
default size).
3) The new window will display the image canvas (alternating white/grey
diagonal lines with a grid-dot overlay) in the center, with a grey margin
surrounding the canvas.
4) If the bottom-right corner of the image window is covered by the "Tool
Modifier Tips" panel, either click the panel's close button to hide it, or move
it so the corner is visible.
5) Move the mouse over the image window's bottom-right corner, and the mouse
cursor should become a "horizontal/vertical resize" cursor (an arrow pointing
towards the lower right).
6) While the resize cursor is visible, click the corner of the window & slowly
drag it towards the upper-left to make the window smaller. The canvas should
stay the same size, and the grey margins should shrink (keeping the canvas
centered in the window).
7) The app-freeze happens at about the point in the resize-drag when there's no
more than a pixel or two of grey margin (or no margin at all). It may take a
few tries to get it to freeze, but once the margins are small, slowly moving
the mouse in a circular motion should eventually trigger it. The point of
moving in a circle is to cause the scrollers to alternate between becoming
visible (when the window becomes smaller than the canvas), and then hiding
again (when the window is larger than the canvas).
8) When the app becomes frozen, the window itself will continue to resize in
response to mouse-dragging, however the window content will stop updating, and
the grey margins will no longer grow & shrink. At this point, the menus &
canvas tools will no longer respond, and a system dialog may eventually appear,
notifying that the window is unresponsive. (Force-quitting the app is
recommended, otherwise it will eventually overflow the stack).
[Regression Potential]
The 1.0 BETA9c fix prevents the crash by updating the custom-layout
functionality to prevent a recursive loop of showing/hiding the scrollers. It
has been tested & verified that the crash no longer appears, and although no
issue has been found, the most likely regression from preventing the
recursive-layout loop would be that the scrollview layout would become
out-of-sync with the window size. Although this is rather unlikely (layout
should happen at least once nonrecursively), the unsynced-layout would just be
a cosmetic issue - no stack overflow, so the app would continue to run &
interact.
[Other Info]
The 1.0 BETA9c update also contains a fix for a different issue: PikoPixel
had a cosmetic issue on the KDE-Plasma, MATE, & Xfce desktop environments (the
issue's with the environments' window managers rather than the desktops
themselves) where maximizing an image window would leave transparent gaps at
the edges of the window, due to a framework issue that can incorrectly
calculate windows' X11 decoration sizes.
The same issue appears when PikoPixel runs on LXDE & Window Maker desktops,
and PP already had a workaround in place for those environments.
The BETA9c update enables the existing LXDE/WM workaround when PikoPixel
runs on KDE/MATE/Xfce. The workaround has been tested & verified (in addition
to testing on previous releases in the workaround's original target
environments).
** Affects: pikopixel.app (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1770777
Title:
[SRU] Bionic: PikoPixel 1.0 BETA9b can crash when resizing a document
window
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