[Marble-devel] Marble crash when you scrolling a map in "Flat Map" projection

[Torsten Rahn]

Hi,

I can confirm this crash happening in master - however even on a pretty speedy 
machine.

It happened to me about  a week ago when I did pretty much what you described 
(zooming while panning at the top of the flat map projection).
I also looked at the backtrace back then and also figured that the allowed 
range of values for the position in the tile had been exceeded.

I didn't have enough time to investigate it further though.

I guess it has been there since the inertial panning has been there:

The Texturerendering assumes rendering to happen within the same zoom level 
(unless it becomes aware that it has changed).
I suspect that the combination of threaded rendering, changing zoom level 
while panning and the access of pixels near the pole area exposes a corner 
case which leads to the problem you mention.

It would be nice if this problem could be understood in a better way. Oleg: 
could you look into it?

Nevertheless I think it it would be a good  idea to introduce "guards" inside 
pixel() an pixelF() the way you suggest them in your patch: 

However the actual lines should include include an "else":

if (x < 0) x = 0;
else if (x > m_resultTile.width()) x = m_resultTile.width();

if (y < 0) y = 0;
else if (y > m_resultTile.height()) y = m_resultTile.height();

I suspect that this might also get rid of the random crashes that we have seen 
on the mobile version.
In terms of render quality the user will not notice the "wrong values" since 
they only affect very few pixels. It might or might not make sense to switch 
these guards off during the development of Marble. 

Best Regards,
Torsten


On Dienstag, 18. Dezember 2012 07:33:41 Олег Любимов wrote:
> Hi all.
> 
> Marble crashes when you scroll a map and change zoom level in the "Flat
> Map" projection. This bug has reproducing probability 80-90% (100% if you
> use slow hardware). The bug is reproduced on Desktop and on QML marble
> application.
> Reproducing:
> 1. Download sources, build(QT only, Debug), install and run marble
> 2. Check a map witch has tile level more than 1. I checked "Historical Map
> 1689"
>  3. When the map is opened, set a Projection to "Flat Map" set zoom to
> minimum, and drag the map (it will be looked sush as a tape) to the Top
> Bourder (or Bottom Bourder) of Marble Widget.
> 4. Press left mouse and scroll the map from left to right (the map should
> scrolling by "inertia" several seconds after you release left mouse button)
> 5. When the will be scrolling by "inertia", you should increase or decrease
> zoom of the map and grag it from Top to Bottom(Bottom to Top).
> 6. After several reps of the 4 and 5 steps the Error should be accours.
> Sometimes is reproduce in the first rep, but often you should make 5 - 20
> reps of 4 and 5 steps.
> 
> Marble version is 1.4.9 (1.5.0 RC 1) Operating system Xubuntu 11.10 Qt
> version 4.8.1
> 
> Does anybody have this
> problem?(https://bugs.kde.org/show_bug.cgi?id=311624)
> 
> ------- GDB
> log------------------------------------------------------------------------
> ---------------------------------------------------------------------------
> ------------------------------------------------- Program received signal
> SIGSEGV, Segmentation fault.
> [Switching to Thread 0xb3bffb40 (LWP 17144)]
> Marble::StackedTile::pixel (this=0xb3d0c3f8, x=559, y=-2027) at
> /home/olyubimov/git_repository/marble/src/lib/StackedTile.cpp:262
> 262 return d->pixel( x, y );
> (gdb) ba
> #0 Marble::StackedTile::pixel (this=0xb3d0c3f8, x=559, y=-2027) at
> /home/olyubimov/git_repository/marble/src/lib/StackedTile.cpp:262
> #1 0x012b6f22 in Marble::ScanlineTextureMapperContext::pixelValueApprox
> (this=0xb3bff1ec, lon=-0.90835936550699259, lat=1.5724603059378008,
> scanLine=<optimized out>, n=8) at
> /home/olyubimov/git_repository/marble/src/lib/ScanlineTextureMapperContext.
> cpp:338 #2 0x012b9245 in
> Marble::EquirectScanlineTextureMapper::RenderJob::run (this=0x89dbb90)
> at
> /home/olyubimov/git_repository/marble/src/lib/EquirectScanlineTextureMapper
> .cpp:231 #3 0x0018d39b in QThreadPoolThread::run (this=0x8b9a2a0) at
> concurrent/qthreadpool.cpp:107
> #4 0x0019ade0 in QThreadPrivate::start (arg=0x8b9a2a0) at
> thread/qthread_unix.cpp:298
> #5 0x0179fd4c in start_thread () from /lib/i386-linux-gnu/libpthread.so.0
> #6 0x016ddd3e in clone () from /lib/i386-linux-gnu/libc.so.6
> ---------------------------------------------------------------------------
> ---------------------------------------------------------------------------
> ----------------------------------------------------------------- I my
> personal opinion this bug is generated when function
> Marble::StackedTile::pixel (this=0xb3d0c3f8, x=559, y=-2027) takes
> arguments with invalid values. I create simple patch (see attachment) to
> add code, which limits the arguments. Because "x" and "y" args are the
> pixel values the bottom bound or this args is 0, and the top bounds of the
> args is QImage m_resultTile.width() and QImage m_resultTile.heidth(). If
> you limit the "x" and "y" args by this bounds the bug not reproduces.
> 
> <http://postimage.org/image/5h0b2pf4r/>