[fpc-pascal] dglOpenGL <-> GL, GLu, GLExt

[Juha Manninen]

On Sun, Feb 17, 2013 at 11:12 PM, Marco van de Voort <marcov at stack.nl> wrote:
>> Q: how am I supposed to initialize OpenGL when using units provided by FPC?
>
> The unit does it at startup. That has as disadvantage that the filename
> can't be changed (or at least that first try can't be avoided).
>
> After that, you iirc need to do load<something with glversion> from unit
> glext to load the extensions for later versions.


Thanks Marco.

I didn't quite understand what is load<something with glversion>.

My experiments advance slowly. The original DeleD code validate OpenGL
by checking if
    @glActiveTextureARB, @glClientActiveTextureARB and @glMultiTexCoord2fARB
are assigned.

With dglopengl it stops working when I replace
  H_RC := wglCreateContext(H_DC);
with the cross-platform OpenGLContext:
  fOpenGLControl1:=TOpenGLControl.Create(Self);
and replace
  wglMakeCurrent(H_DC, H_RC);
with
  OpenGLControl1.MakeCurrent;

When using GLExt (provided by FPC), the test still fails but then I
can remove it and the code does not crash later.
So, maybe it is better to use GL and GLExt.
If I put the same test in the OpenGlControl demo in Lazarus, it does
not fail! I don't see what makes the difference.

Cross-platform OpenGL still does not work though. Deled 3-D uses form
inheritance and all forms needing OpenGL drawing window inherit from
TOGLForm. I copy below the Create method where I had to comment out
most code to make it compile.
I create fOpenGLControl1 the same way than in the Lazarus example, but
I don't know what to put into the OnPaint and OnResize event handlers.
Now the code does not crash but obviously does not draw anything either.

I guess I must study the topic more. I will commit my code to the
DeleD SVN branch although it is broken. Maybe someone could have a
look at it.

Regards,
Juha


----------------------------

constructor TOGLForm.Create(AOwner: TComponent);
//var PixelFormat: Integer;
           // our windows pixel format
//    PFD: PixelFormatDescriptor;
           // describes the pixel format
begin
    inherited;
    Initialize;
    Set8087CW($133f);    // disable fpu exceptions when doing OpenGL rendering

    //ZeroMemory(@PFD, SizeOf(PFD));
           // describe our Pixel Format Descriptor
    //with PFD do begin
    //    nSize := SizeOf(PFD);
    //    nVersion := 1;
    //    dwFlags := PFD_DRAW_TO_WINDOW or PFD_SUPPORT_OPENGL or
PFD_DOUBLEBUFFER or 0;
    //    iPixelType := PFD_TYPE_RGBA;
    //    cColorBits := 16;
    //    cDepthBits := 16;
    //end;

    // now set pixel format + initialize rendering context
    //H_DC := Canvas.Handle;
    //PixelFormat := ChoosePixelFormat(H_DC, @PFD);
           // choose a pixel format based on our description
    //if PixelFormat = 0 then begin
    //    KillWindow;
    //    MessageBox(0, 'Unable to choose pixel format', 'Error',
MB_OK or MB_ICONERROR);
    //    Exit;
    //end;
    //if not SetPixelFormat(H_DC, PixelFormat, @PFD) then begin
           // attach the pixel format to the window
    //    KillWindow;
    //    MessageBox(0, 'Unable to set pixel format', 'Error', MB_OK
or MB_ICONERROR);
    //    Exit;
    //end;
    //H_RC := wglCreateContext(H_DC);
           // get the rendering context handle
    //if H_RC = 0 then begin
    //    KillWindow;
    //    MessageBox(0, 'Unable to create rendering context', 'Error',
MB_OK or MB_ICONERROR);
    //    Exit;
    //end;
    //ActivateRenderingContext(H_DC,H_RC);
    fOpenGLControl1:=TOpenGLControl.Create(Self);
    with fOpenGLControl1 do begin
      Name:='OpenGLControl1';
      Parent:=Self;
      SetBounds(10,90,380,200);
      //OnPaint:=@OpenGLControl1Paint;
      //OnResize:=@OpenGLControl1Resize;
    end;
    if not fOpenGLControl1.MakeCurrent then begin
          // initialize the endering context
        KillWindow;
        MessageBox(0, 'Unable to activate rendering context', 'Error',
MB_OK or MB_ICONERROR);
        Exit;
    end;
end;