7 replies to this topic

[Ussyless]

Greetings, so i'm trying to use vertex buffer objects, however, glGenBuffers is throwing me an access violation

 

Checklist time:

i have glew installed.

i have freeglut installed

included in this order

 

#include <GL/glew.h>

#include <GL/wglew.h>

#include <GL/freeglut.h>

i have a linkers to the appropriate libraries, (glew32, freeglut) unless i missed something

i have run glewinit (both before and after glutinit on seperate attempts)

genbuffers is run as follows

...

GLuint VBO = 0;

void init(){    

    float temp[]={10,10,20,10,10,20};

    glGenBuffers(1,&VBO);

...

according to the utilities included in glew, my open gl version is

version string: 4.2.11931

 

 

any help?

 

i can provide more code if needed

Edited by Ussyless, 19 February 2013 - 08:43 PM.

[BitMaster]

Have you called glewInit() once before calling glGenBuffers in your program and did it return GLEW_OK? If you did, how does the driver identify itself (name/version/possibly the extension string)?

[Ussyless]

yeah, i have run glewinit, i'll check that other stuff in a sec and see how it is

[BitMaster]

Have you called glewInit and verified its return value? Just calling glewInit won't be enough, there are plenty of things that can go wrong (most often calling it before an OpenGL context exists or when no context is current).

[Ussyless]

i have tried calling it both before and after the context exists, though currently it's being called before, wasn't sure when it needed to be initialised since it's included before and DevIL is initialised before also

 

anyway, currently if i run 

 

    GLenum errr= glewInit();    

    GLenum x;

    x=GLEW_OK;

    glutInit(&argc,argv);

glewinit returns a 1, and GLEW_OK returns a 0 so i assume they are different enums

 

ah there we go, after moving it to after the context, it works fine, both enums return 0, so it's GLEW_OK, and glgenbuffers no longer send a access violation

 

i feel stupid now, i swear i did try this, but thanks for asking the right questions

 

 

perhaps a small side-question ( perhaps not ), are there any standard libraries/functions i can use to pop up a window in case of for example, a error or a specific scenario easily? (ideally something along the lines of windows::showSplashScreen() or showSplashScreen("An error!") or something like that, doesnt even need text or anything, just some external indicator that something has happened without breakpoints.)

 

edit: messagebox

 

thanks

Edited by Ussyless, 20 February 2013 - 04:50 AM.

[Brother Bob]

The rendering context is created when you call glutCreateWindow, so you cannot call glweInit before that.

[BitMaster]

perhaps a small side-question ( perhaps not ), are there any standard libraries/functions i can use to pop up a window in case of for example, a error or a specific scenario easily? (ideally something along the lines of windows::showSplashScreen() or showSplashScreen("An error!") or something like that, doesnt even need text or anything, just some external indicator that something has happened without breakpoints.)

For any non-trivial program I would suggest having a decent logging mechanism in place (at least writing stuff to the console, better to both the console and a file). With a simple macro all logging overhead can be completely removed by #undefing a single define (like _DEBUG which is already prepared for you with MSVC default configurations).
Apart from that asserts are also extremely useful because they will reliably trigger an attached debugger in debug builds but will be completely compiled out in release builds.

That said, for something as fundamental as basic initialization, I would not hesitate to use exceptions. Wrap everything in main() inside a suitable try/catch block, place a constant breakpoint into the catch part and rigorously check all initialization steps, throwing a suitably descriptive std::runtime_error when anything fails in an unrecoverable way. Obviously a published program needs to do something smarter, but "std::cout << exc.what() << std::endl" will do during development.

[BornToCode]

glewInit uses the render context that is current. So until you have OpenGL initialize and have wglMakeCurrent set up with a render context glewInit will fail