Some problems of using opengl es in qt

[halftone]

when I ported my code which is developed by opengl es from windows framework to qt framework, some run errors occured in functions such as "glDrawElements" .
Are there some differences between qt framework and windows in using buffer objects or kind of "glDrawElements" function ?

[ixSci]

I'm sure you will have the more appropriate advices when others can see your code and what is wrong with it.

[halftone]

when I was using qt with opengl es, in my render code, I used VBO in the way just like in win32 project, the code is the following:

@
void DrawMesh()

{
#if 1
glDisableClientState(GL_NORMAL_ARRAY);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);
GLuint buf1,buf2;
glGenBuffers(1,&buf1);
glBindBuffer(GL_ARRAY_BUFFER,buf1);
GLfloat a[]={
0.0f, 0.0f, 0.0f, 0.0f,
1.0f, 0.0f, 0.0f, 1.0f,
0.0f, 1.0f, 0.0f, 2.0f
};

GLushort index[] = {
0,1,2
};
glBufferData(GL_ARRAY_BUFFER,12sizeof(GLfloat),a,GL_STATIC_DRAW);
glEnableClientState(GL_VERTEX_ARRAY);
glVertexPointer(3,GL_FLOAT,4sizeof(GL_FLOAT),0);
glGenBuffers(1,&buf2);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER,buf2);
glBufferData(GL_ELEMENT_ARRAY_BUFFER,3*sizeof(GLushort),index,GL_STATIC_DRAW);
glDrawElements(GL_TRIANGLES,3,GL_UNSIGNED_SHORT,0);
glDisableClientState(GL_VERTEX_ARRAY);
#endif
}
@

when run to "glDrawElements(GL_TRIANGLES,3,GL_UNSIGNED_SHORT,0);" error occured "Unhandled exception at 0x0239faec in hellogl_es2.exe: 0xC0000005: Access violation reading location 0x00000000. "
I want to know why this happened?

here if I remove VBO parts, no error occured, how to use VBO in QT?

[olihey]

Hej,

I am not sure if that helps you with your problem but I had a similar problem when using VBOs in the QGLWidget on Windows. It worked fine on the Mac ;)

Anyway seems like you have to get the function pointers to some OpenGL calls before you can use them.

Here are some snippets from my code

In the header:
@#ifdef WIN32
#include <windows.h>
#include <GL/gl.h>

#include "OGL/glext.h"

extern PFNGLGENBUFFERSPROC glGenBuffers;
extern PFNGLBINDBUFFERPROC glBindBuffer;
extern PFNGLDELETEBUFFERSPROC glDeleteBuffers;
extern PFNGLBUFFERDATAPROC glBufferData;
#endif
@

and when initializing OpenGL do that (UIWidgetScene is my subclass of QGLWidget

@void UIWidgetScene::initializeGL()
{
#ifdef WIN32
// get the pointer to the GL functions
glGenBuffers = (PFNGLGENBUFFERSPROC) wglGetProcAddress("glGenBuffers");
glBindBuffer = (PFNGLBINDBUFFERPROC) wglGetProcAddress("glBindBuffer");
glDeleteBuffers = (PFNGLDELETEBUFFERSPROC) wglGetProcAddress("glDeleteBuffers");
glBufferData = (PFNGLBUFFERDATAPROC) wglGetProcAddress("glBufferData");
_canVBO = (NULL != glGenBuffers) && (NULL != glBindBuffer) && (NULL != glDeleteBuffers) && (NULL != glBufferData);
#else
// Mac supports VBO out of the box, GET A MAC!!!!
_canVBO = true;
#endif

..... do the other OpenGL stuff .....

@

Hope that helps,
Oli

[halftone]

but error occured that "PFNGLGENBUFFERSPROC , PFNGLBINDBUFFERPROC , PFNGLDELETEBUFFERSPROC , PFNGLBUFFERDATAPROC not defined" , I searched in the network, it said that these defines in gl/glext.h , so I download opengl files including glext.h , put it into "C:\Program Files\Microsoft Visual Studio 9.0\VC\include\gl" , but it doesn't work

[olihey]

Well, I'didn't put the glext.h in the path you did!
I just placed it in the subdirectory "OGL" in my project root!

I am not sure why they aren't defined.

I have the first snippet of code at the top of my header file before including any other files.