octave qt graphical interface fails

[Jussi Eloranta]

Starting octave qt-based gui on either rapsberry pi 3 or 4 (either with or without the kernel graphics driver) does not work. It functions through the couple of initial dialogs (on first run) but the main window is unresponsive and the octave process eats 100% CPU. The screen is also garbled. The only way to get rid of it is to do kill -9 ...

Even the text based octave does not work too well. Plotting does not work (opens the window but nothing actually shows).

This is on up to date Raspbian Buster (as of 9/11/2019).

[Edward Vidal Jr (develone)]

Following the upgrade RP4 from stetch to buster.
testfile "im1.m"

clear
%close all
I = imread("thumb0000.bmp");
figure;
imagesc(I);
colormap 'gray'
colorbar;
grid;

Octave fails to plot
On the raspbian IRC it was recommended to try with LIBGL_ALWAYS_SOFTWARE=true
This did not help.
I posted on octave IRC and was told that this was a raspbian bug.

GNU Octave - Bugs: PMbug #56570, unable to plot with OpenGL on... [Savannah]

LIBGL_ALWAYS_SOFTWARE=true octave
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octave:1> ls *.bmp
r1thumb0000.bmp r4thumb0000.bmp t250thumb.bmp t300thumb.bmp tt.bmp
r2thumb0000.bmp r5thumb0000.bmp t260thumb.bmp thumb0000.bmp
r3thumb0000.bmp r6thumb0000.bmp t275thumb.bmp thumb.bmp
octave:2> im1
warning: opengl_renderer: Error 'invalid enumerant' (1280) occurred in init_gl_context
warning: called from
    allchild at line 40 column 7
    newplot at line 202 column 11
    image at line 113 column 11
    imagesc at line 98 column 12
    im1 at line 5 column 1
warning: opengl_renderer: Error 'invalid operation' (1282) occurred drawing 'text' object
warning: called from
    allchild at line 40 column 7
    newplot at line 202 column 11
    image at line 113 column 11
    imagesc at line 98 column 12
    im1 at line 5 column 1
warning: opengl_renderer: Error 'invalid enumerant' (1280) occurred in init_gl_context
warning: called from
    newplot at line 203 column 11
    image at line 113 column 11
    imagesc at line 98 column 12
    im1 at line 5 column 1
warning: opengl_renderer: Error 'invalid operation' (1282) occurred drawing 'text' object
warning: called from
    newplot at line 203 column 11
    image at line 113 column 11
    imagesc at line 98 column 12
    im1 at line 5 column 1
octave:3> warning: opengl_renderer: Error 'invalid enumerant' (1280) occurred in init_gl_context
warning: opengl_renderer: Error 'invalid operation' (1282) occurred drawing 'text' object
warning: opengl_renderer: Error 'invalid operation' (1282) occurred drawing 'image' object
warning: opengl_renderer: Error 'invalid enumerant' (1280) occurred drawing 'axes' object
warning: opengl_renderer: Error 'invalid operation' (1282) occurred drawing 'text' object
warning: opengl_renderer: Error 'invalid operation' (1282) occurred drawing 'image' object
warning: opengl_renderer: Error 'invalid enumerant' (1280) occurred drawing 'axes' object
warning: opengl_renderer: Error 'invalid enumerant' (1280) occurred in init_gl_context
warning: opengl_renderer: Error 'invalid operation' (1282) occurred drawing 'text' object
warning: opengl...

[Jussi Eloranta (eloranta)]

A workaround is to tell octave to use gnuplot:

graphics_toolkit("gnuplot");

At least this worked now:

x = 0:0.01:2*pi;
y=sin(x);
plot(x,y);

One can place it in octave rc file for automatic loading.

But still it would be nice to see this bug fixed. And there is no way to run the gui as it gets stuck and eats 100% cpu.