Some OpenGL functions do not load proprerly.

[chronozphere]

Hey guy's

I'm trying to learn OpenGL, but it's not going as fast as i hoped for. I want to render a quad using a VBO. I made the following class:

[pascal]
TVertexBuffer = class
private
fVBOVertices: TGLUInt;
fVBONormals: TGLUInt;
public
fVertices: array of TGLVector3f;
fNormals: array of TGLVector3f;

constructor Create();
destructor Destroy(); override;

procedure Update();
procedure Render();
end;

{ TVertexBuffer }
constructor TVertexBuffer.Create;
begin
glGenBuffersARB(1, @fVBOVertices);
glGenBuffersARB(1, @fVBONormals);
end;

destructor TVertexBuffer.Destroy;
begin
glDeleteBuffersARB(1, @fVBOVertices);
glDeleteBuffersARB(1, @fVBONormals);

inherited;
end;

procedure TVertexBuffer.Render;
begin
//Enable client states
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_NORMAL_ARRAY);

//bind vertices
glBindBufferARB(GL_ARRAY_BUFFER_ARB, fVBOVertices);
glVertexPointer(3, GL_FLOAT, 0, nil);

//bind normals
glBindBufferARB(GL_ARRAY_BUFFER_ARB, FVBONormals);
glNormalPointer(GL_FLOAT, 0, nil);

//Render it now!
glDrawArrays(GL_TRIANGLES,0,Length(fVertices)-1);

//Disable client states
glDisableClientState(GL_VERTEX_ARRAY);
glDisableClientState(GL_NORMAL_ARRAY);
end;

procedure TVertexBuffer.Update;
begin
//load vertices
glBindBufferARB(GL_ARRAY_BUFFER_ARB, fVBOVertices);
glBufferDataARB(GL_ARRAY_BUFFER_ARB, Length(fVertices)*sizeof(TGLVector3f),
fVertices, GL_STATIC_DRAW_ARB);

//Load normals
glBindBufferARB(GL_ARRAY_BUFFER_ARB, FVBONormals);
glBufferDataARB(GL_ARRAY_BUFFER_ARB, Length(fNormals)*sizeof(TGLVector3f),
fNormals, GL_STATIC_DRAW_ARB);

SetLength(fVertices,0);
SetLength(fNormals,0);
end;

[/pascal]

It's simple. User fills the vertex and normal array's and calls update. The VBO is rendered every frame.

But as soon as i try to call a routine like glGenBuffersARB, an AV pops up with adress 00000000. I know this means the function-variable is not assigned.

I'm using the latest version of the dglOpenGL.pas header and the very first thing i do in my application is this:

[pascal]
InitOpenGL();
ReadImplementationProperties;
ReadExtensions;
[/pascal]

ReadExtensions calls Read_GL_ARB_buffer_object which loads the routines i'm using here. But they appear not to be assigned. I even called glGetString to get a list of the extensions, and GL_ARB_vertex_buffer_object is on that list. But somehow, the routines don't seem te be assigned. :cry:

What is happening here? I have a nice 8600GT with fairly recent drivers. How come i can't create/use any VBO's?

Can anyone help me?

Thanks.

[Luuk van Venrooij]

What delphi are you using? The latest headers give problems with Delphi 2009 and unicode.

[chronozphere]

I just discovered something that might have caused this.

I was calling:

[pascal]
ReadImplementationProperties;
ReadExtensions;
[/pascal]

while no rendercontext was activated. glProcedure, who assigns adresses to all the procvars failed miserably. So tons of procs weren't initialized.

I tried to manualy load the functions by using:

[pascal]
type
PFNGLBINDBUFFERARBPROC = procedure(target: GLenum; buffer: GLuint); stdcall;
PFNGLDELETEBUFFERSARBPROC = procedure(n :GLsizei; const buffers: PGLuint); stdcall;
PFNGLGENBUFFERSARBPROC = procedure(n :GLsizei; buffers: PGLuint); stdcall;
PFNGLBUFFERDATAARBPROC = procedure(target: GLenum; size: integer; const data: pointer; usage: GLenum); stdcall;

const
GL_ARRAY_BUFFER_ARB = $8892;
GL_STATIC_DRAW_ARB = $88E4;

var
glGenBuffersARB: PFNGLGENBUFFERSARBPROC = nil;
glBindBufferARB: PFNGLBINDBUFFERARBPROC = nil;
glBufferDataARB: PFNGLBUFFERDATAARBPROC = nil;
glDeleteBuffersARB: PFNGLDELETEBUFFERSARBPROC = nil;

{....}
//PROCVAR ASSIGNMENTS
glGenBuffersARB := wglGetProcAddress('glGenBuffersARB');
glBindBufferARB := wglGetProcAddress('glBindBufferARB');
glBufferDataARB := wglGetProcAddress('glBufferDataARB');
glDeleteBuffersARB := wglGetProcAddress('glDeleteBuffersARB');
[/pascal]

And it worked, but it's a messy workaround. During the last tests i outcommented the procvar-assignments and continued debugging. I should have outcommented all the code shown above, because the procedure-variables hid the variables in dglOpenGL.pas, because they had the same name. The variables in my app never got initialized, so the AV kept popping up. Basicly i created my own bug by not cleaning up the mess. :shock:

[Luuk van Venrooij]

personally i call

ReadImplementationProperties;
ReadExtensions

after i have initializedmy window and context.