i already posted this ineffectively to comp.graphics.api.opengl and on this board (but in the wrong section, they kindly directed me here).
I’ve got a strange problem that solely occurs
in my OpenGL app using glut (v3.7):
Whenever i scroll the mouse wheel forwards,
the program exits giving a segmentation fault.
When i scroll the wheel backwards, nothing happens. I have two subwindows and the mouse functions for each of them work fine, also the three buttons work as expected.
Libraries i use: X11, Xi ,Xm, glut, GL and GLU.
I’m on redhat9 using a MS Intellimouse (optical,usb) and scrolling with the mouse wheel works fine otherwise (see the mouse section of my XF86Cconfig below).
Since i can only use an usb mouse on my laptop, i have not yet tried other mice.
Has anybody got an idea what’s going on
or what i could do to solve this?
I’ve already looked at alternatives like glfw but hesitate before porting.
Regards and THANKS,
Option “Protocol” “IMPS/2”
Option “Device” “/dev/input/mice”
Option “ZAxisMapping” “4 5”
Option “Emulate3Buttons” “no”
Very loosely I’d say it’s an “off by one error”. Have you tried to debug the app, watching the values returned by the mouse button pressed?
i didn’t debug yet, thanks for your suggestion. I’ll have to look how to do it.
I’m not quite sure what you mean with ‘off by one’: a unique error only occuring in my app?
“Off by one” is a “more common than it should” programming error where somebody created a memory buffer, say, from 0 to 9 - but the actual code slips and thinks it is from 1 to 10, bites at the end of the buffer and dies with a segfault.
I think that I have found the problem. The scroll wheel sends mouse buttons 4 and 5, but an array of menu ids in the window structure only allowed for a 3 button mouse. Scrolling forward in a subwindow will effectively try to use the window’s parent pointer as a menu id. Scroll back would try to use a child window pointer if any.
I sent a bug report and we’ll see what official fix comes of it. For a quick hack (if you don’t mind recompiling glut) you can either:
- try changing the ‘#define GLUT_MAX_MENUS 3’ in glutint.h to 5
- validate the index of menu in glut_event.c line 425 (menuNum = window->menu[event.xbutton.button - 1]
I did the second and it ‘seems’ to work.
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