Hiya,

Im trying to experiment with VBO's and Ive come a bit unstuck, I found
a tutorial and tried to get it to work with glut but i keep getting the
error "instruction at "0x00000000" referenced to memory at
"0x00000000". the memory could not read"

ive tried using printf to help me debug it, and I think the error is on
this line "glGenBuffersARB(1, &buffer);" as it crashes at this line

can anyone tell me what im doing wrong??

thanks

David


[CODE]

#include <GL/glut.h>
#include <stdlib.h>
#include <stdio.h>
#include <GL/glu.h>
#include "glext.h"

GLfloat data[] = { -1.0f, 1.0f, 0.0f,
				 -1.0f, -1.0f, 0.0f,
				 1.0f, -1.0f, 0.0f };

GLuint buffer;

PFNGLBINDBUFFERARBPROC glBindBufferARB = NULL;
PFNGLGENBUFFERSARBPROC glGenBuffersARB = NULL;
PFNGLBUFFERDATAARBPROC glBufferDataARB = NULL;

void init(void)
{
	// enable depth testing
	glEnable(GL_DEPTH_TEST);
	glDepthFunc(GL_LEQUAL);
	glEnableClientState(GL_VERTEX_ARRAY);
	glClearColor(0.5f, 0.5f, 1.0f, 1.0f);
}

void display(void)
{
		glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
		glMatrixMode(GL_MODELVIEW);
		glLoadIdentity();
		glTranslatef(0, 0, -3);
    	        glBindBufferARB(GL_ARRAY_BUFFER_ARB, buffer);
		glVertexPointer(3, GL_FLOAT, 0, 0);
		glDrawArrays(GL_TRIANGLE_STRIP, 0, 3);
}

void reshape(int w, int h)
{
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	gluPerspective(45, (float) 640 / (float) 480, 1, 512);
}

int main(int argc, char **argv)
{
   	glBindBufferARB =
(PFNGLBINDBUFFERARBPROC)wglGetProcAddress("glBindBufferARB");
	printf("1\n");
    glGenBuffersARB =
(PFNGLGENBUFFERSARBPROC)wglGetProcAddress("glGenBuffersARB");
	printf("2\n");
    glBufferDataARB =
(PFNGLBUFFERDATAARBPROC)wglGetProcAddress("glBufferDataARB");
    printf("3\n");

    glGenBuffersARB(1, &buffer);
	printf("4\n");
    glBindBufferARB(GL_ARRAY_BUFFER_ARB, buffer);
	printf("5\n");
    glBufferDataARB(GL_ARRAY_BUFFER_ARB, sizeof(data), data,
GL_STATIC_DRAW_ARB);
    printf("6\n");
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGB);
    glutInitWindowSize(640, 480);
    glutInitWindowPosition(100, 100);
    glutCreateWindow(argv[0]);
    init();
    glutDisplayFunc(display);
    glutReshapeFunc(reshape);
    glutMainLoop();
    return 0;
}

[/CODE]

googlinggoogler@hotmail.com wrote:

> Hiya,
> 
> Im trying to experiment with VBO's and Ive come a bit unstuck,
> I found a tutorial and tried to get it to work with glut but i
> keep getting the error "instruction at "0x00000000" referenced
> to memory at "0x00000000". the memory could not read"
> 
> ive tried using printf to help me debug it, and I think the
> error is on this line "glGenBuffersARB(1, &buffer);" as it
> crashes at this line
> 
> can anyone tell me what im doing wrong??

You're not checking the function pointer returned by
wglGetProcAdress for being not NULL. Additionally you need a
valid context which is _after_ a GLUT Window has been created
with glutCreateWindow. The best is to do such stuff immediately
before calling glutMainLoop();

-- 
Wolfgang Draxinger

<googlinggoogler@hotmail.com> wrote in message 
news:1112037518.964258.239230@z14g2000cwz.googlegroups.com...
> Hiya,
>
> Im trying to experiment with VBO's and Ive come a bit unstuck, I found
> a tutorial and tried to get it to work with glut but i keep getting the
> error "instruction at "0x00000000" referenced to memory at
> "0x00000000". the memory could not read"
>
> ive tried using printf to help me debug it, and I think the error is on
> this line "glGenBuffersARB(1, &buffer);" as it crashes at this line
>
> can anyone tell me what im doing wrong??
>
> thanks
>
> David
>
>
> [CODE]
>
> #include <GL/glut.h>
> #include <stdlib.h>
> #include <stdio.h>
> #include <GL/glu.h>
> #include "glext.h"
>
> GLfloat data[] = { -1.0f, 1.0f, 0.0f,
> -1.0f, -1.0f, 0.0f,
> 1.0f, -1.0f, 0.0f };
>
> GLuint buffer;
>
> PFNGLBINDBUFFERARBPROC glBindBufferARB = NULL;
> PFNGLGENBUFFERSARBPROC glGenBuffersARB = NULL;
> PFNGLBUFFERDATAARBPROC glBufferDataARB = NULL;
>
> void init(void)
> {
> // enable depth testing
> glEnable(GL_DEPTH_TEST);
> glDepthFunc(GL_LEQUAL);
> glEnableClientState(GL_VERTEX_ARRAY);
> glClearColor(0.5f, 0.5f, 1.0f, 1.0f);
> }
>
> void display(void)
> {
> glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
> glMatrixMode(GL_MODELVIEW);
> glLoadIdentity();
> glTranslatef(0, 0, -3);
>            glBindBufferARB(GL_ARRAY_BUFFER_ARB, buffer);
> glVertexPointer(3, GL_FLOAT, 0, 0);
> glDrawArrays(GL_TRIANGLE_STRIP, 0, 3);
> }
>
> void reshape(int w, int h)
> {
> glMatrixMode(GL_PROJECTION);
> glLoadIdentity();
> gluPerspective(45, (float) 640 / (float) 480, 1, 512);
> }
>
> int main(int argc, char **argv)
> {
>   glBindBufferARB =
> (PFNGLBINDBUFFERARBPROC)wglGetProcAddress("glBindBufferARB");

You are not checking for errors here.

> printf("1\n");
>    glGenBuffersARB =
> (PFNGLGENBUFFERSARBPROC)wglGetProcAddress("glGenBuffersARB");
> printf("2\n");
>    glBufferDataARB =
> (PFNGLBUFFERDATAARBPROC)wglGetProcAddress("glBufferDataARB");
>    printf("3\n");
>
>    glGenBuffersARB(1, &buffer);

what is 'buffer'?

Allan

Allan Bruce wrote:

> ... 
>> GLuint buffer;
>>
>> PFNGLBINDBUFFERARBPROC glBindBufferARB = NULL;
>> PFNGLGENBUFFERSARBPROC glGenBuffersARB = NULL;
>> PFNGLBUFFERDATAARBPROC glBufferDataARB = NULL;
>>
>> void init(void)

>  [...]

>>>    glGenBuffersARB(1, &buffer); 
> 
> what is 'buffer'?

It's the variable defined a few lines above init(). No problem
there. The real problem is, that the call to wglGetProcAddress
happens at a point, where no context has been created yet.

-- 
Wolfgang Draxinger

Thank you! thats great ive moved a step further...

im having a new problem now though....

basically ive moved the "wglGetProcAddress" commands into my init()
function and ive dropped the "glGenBuffersARB, glBindBufferARB,
glBufferDataARB" to above the call to glutMainLoop()

Now im presented with a window that doesnt display anything and
basically crashes grabbing the screen from behind and holding this
within the frame and not displaying anything useful

Sorry to pesters I can't see the error thats all :-)

cheers!

David

googlinggoogler@hotmail.com wrote:

> Thank you! thats great ive moved a step further...
> 
> im having a new problem now though....
> 
> basically ive moved the "wglGetProcAddress" commands into my
> init() function and ive dropped the "glGenBuffersARB,
> glBindBufferARB, glBufferDataARB" to above the call to
> glutMainLoop()
> 
> Now im presented with a window that doesnt display anything and
> basically crashes grabbing the screen from behind and holding
> this within the frame and not displaying anything useful

How about a glutSwapBuffers() at the end of display()? Also I'd
create a window with a depth buffer, since depth test is quite
useless without it, so
glutInitDisplayMode(GLUT_RGB|GLUT_DEPTH|GLUT_DOUBLE).

Also I suspect you want a lot model (because without you will
just see a "flat" silouhette). Then remember, that ligting
ignores glColor and expects the use of glMaterial, however for
conveniece you can link the call of glColor to one of the
glMaterial parameters, which can be quite usefull in combination
with glColorPointer.

I also recommend to set glViewport to the dimensions of the
window in reshape(). I very complex rendering situations you
normally do nothing else as this in reshape() and set the proper
projection, the depth test and other stuff in the display()
function. The reason is, that you might render different layers
with different rendering settings.

-- 
Wolfgang Draxinger

> Now im presented with a window that doesnt display anything and
> basically crashes grabbing the screen from behind and holding this
> within the frame and not displaying anything useful

> 
> David

Try Swapping the buffers ;-)

#include <GL/glut.h>
#include <stdlib.h>
#include <stdio.h>
#include <GL/glu.h>
#include <GL/glext.h>

GLfloat data[] = { -1.0f, 1.0f, 0.0f,
     -1.0f, -1.0f, 0.0f,
     1.0f, -1.0f, 0.0f };

GLuint buffer;

PFNGLBINDBUFFERARBPROC glBindBufferARB = NULL;
PFNGLGENBUFFERSARBPROC glGenBuffersARB = NULL;
PFNGLBUFFERDATAARBPROC glBufferDataARB = NULL;

void init(void)
{
 glClearDepth(1.0f);								// Depth Buffer Setup
 glEnable(GL_DEPTH_TEST);							// Enables Depth Testing
 glDepthFunc(GL_LEQUAL);							// The Type Of Depth Testing To Do

 glClearColor(0.5f, 0.5f, 1.0f, 1.0f);
 glBindBufferARB = (PFNGLBINDBUFFERARBPROC)wglGetProcAddress("glBindBufferARB");
 glGenBuffersARB = (PFNGLGENBUFFERSARBPROC)wglGetProcAddress("glGenBuffersARB");
 glBufferDataARB = (PFNGLBUFFERDATAARBPROC)wglGetProcAddress("glBufferDataARB");
 if ((glBindBufferARB == NULL) || (glGenBuffersARB == NULL) ||
(glBufferDataARB == NULL)) {
	printf("Does not support!");
	exit(1);
 }
 glGenBuffersARB(1, &buffer);
 glBindBufferARB(GL_ARRAY_BUFFER_ARB, buffer); 
 glBufferDataARB(GL_ARRAY_BUFFER_ARB, sizeof(data), data,
GL_STATIC_DRAW_ARB);
 glBindBufferARB(GL_ARRAY_BUFFER_ARB, NULL);
}

void display(void)
{
  glDrawBuffer(GL_BACK);
  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
  glTranslatef(0, 0, -3);
  glColor3ub(0, 0, 0);
  glEnableClientState(GL_VERTEX_ARRAY);
  glBindBufferARB(GL_ARRAY_BUFFER_ARB, buffer);
  glVertexPointer(3, GL_FLOAT, 0, 0);
  glBindBufferARB(GL_ARRAY_BUFFER_ARB, NULL);
  glDrawArrays(GL_TRIANGLES, 0, 3);
  glDisableClientState(GL_VERTEX_ARRAY);  

  glutSwapBuffers(); // <----------------------
}

void reshape(int w, int h)
{
	glViewport(0,0,w,h);								// Reset The Current Viewport

	glMatrixMode(GL_PROJECTION);						// Select The Projection Matrix
	glLoadIdentity();									// Reset The Projection Matrix

	gluPerspective(45, (float) 640 / (float) 480, 1, 512);

	glMatrixMode(GL_MODELVIEW);							// Select The Modelview Matrix
	glLoadIdentity();									// Reset The Modelview Matrix
}

int main(int argc, char **argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGB);
    glutInitWindowSize(640, 480);
    glutInitWindowPosition(100, 100);
	glutCreateWindow("Test");
    init();
    glutDisplayFunc(display);
    glutReshapeFunc(reshape);
    glutMainLoop();
	glutPostRedisplay();
    return 0;
}

Cheers! im very gratefull :-) thats helped me no end, now I can do what
ive been wanting to do!

thank you!

David