[Octave-bug-tracker] [bug #49756] Partial or no image shown with imshow, plus consistent Octave crash

[anonymous]

URL:
  <http://savannah.gnu.org/bugs/?49756>

                 Summary: Partial or no image shown with imshow, plus
consistent Octave crash
                 Project: GNU Octave
            Submitted by: None
            Submitted on: Fri 02 Dec 2016 06:53:13 PM UTC
                Category: Plotting
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Crash
                  Status: None
             Assigned to: None
         Originator Name: Marshall
        Originator Email: address@hidden
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 4.2.0
        Operating System: Microsoft Windows

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Details:

I'm using GNU Octave, version 4.2.0, "x86_64-w64-mingw32".
I have several problems related to imshow(). First is that imshow() will not
draw partial pixels when zooming or panning; second, under some conditions,
the entire image doesn't show when the top of the image is not within the
axis; third, I can reproducibly crash octave when panning/dragging the image
up to the top of the screen. 

Obviously the crash has the worst consequences, but problem 2 is what made me
start the bug report. Trying to extract the bare-bones of the problem led to
problem 1, which doesn't reproduce problem 2. I found problem 3 on accident
while trying to create and test this bug report.


%"pixels" disappear when not completely within the axis (zoom or scroll)
figure(1),clf
im=uint8(rand(100,100)*255);
imshow(im)
hold on;
xs=[0 0 1 1 0];ys=[0 1 1 0 0];
xoff=xs-0.5;yoff=ys-0.5;
offset=50;
plot(xs+offset,ys+offset,'rx')
plot(xoff*0.75+0.5+offset,yoff*0.75+0.5+offset,'b')
hold off;
title('nice image')
pause(1)
axc=([0 1 0 1]-.5);
axis(axc*2+.5+offset)%zoom: partial pixels not shown
title('Partial image, whole pixels only')
pause(1)
axis(axc+offset+.5)%zoom more: no pixels shown (background color), plot is.
title('no image, no background (only plot)')

pause(1)
%Whole image disappears when top corners above top axis (zoom or scroll)
% (and image shown below bottom of axis, when bottom is beyond bottom axis and
top not above the top axis)
im=uint8(rand(495,495)*255);
figure(2),clf
imx0 = 60;
imy0 = 70;
imxf = 442;
imyf = 452;
imxF = 9;
imyF = 3000;
imshow(im,'xdata',([1,size(im,1)]-imx0)*imxF/(imxf-imx0),'ydata',([size(im,2),1]-imy0)*imyF/(imyf-imy0))
axis('on','xy','normal')
ax=axis;
title('nice image')
pause(1);
axis(ax*0.99)%zoom: whole image disappears
title('NO IMAGE!')
pause(1);
axis(ax*0.99+[0 0 +100 +100])%scroll: reappears, but extends below bottom
axis
title('Back again! (but below bottom axis)')
pause(1);
axis(ax*0.99)%Scroll back: whole image disappears again.
title('Gone again!')
pause(1);
title('Now lets manually crash octave')
pause(1);
title('manually pan the image to the top of the screen (keep dragging beyond
figure border)')
pan on





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