Delphi OpenGL Drawing

Question

I'm setting up my window like this:

glMatrixMode (GL_PROJECTION);
glLoadIdentity ();
glOrtho (0, form1.Width, form1.height, 0, 0, 1);
glMatrixMode (GL_MODELVIEW);
glDisable(GL_DEPTH_TEST);

And my drawing routine looks like this:

tempdist:=0.3 / distance(i,0,1,2);
xunit:=1 div 90;
zunit:=1 div 74;
glBegin(GL_LINE_LOOP);
case players[i].isteam of
2:glcolor3f(1.0,0.0,0.0); //Terrorist
3:glcolor3f(0.0,0.0,1.0); //Counter-Terrorist
end;
glvertex2f((thetax / 100)*xunit,(thetaz / 100)*zunit);
glvertex2f((thetax / 100)*xunit+tempdist,(thetaz / 100)*zunit);
glvertex2f((thetax / 100)*xunit+tempdist,(thetaz / 100)*zunit+tempdist);
glvertex2f((thetax / 100)*xunit,(thetaz / 100)*zunit+tempdist);
glEnd();
SwapBuffers(wglGetCurrentDC);

No sign of drawing whatsoever. Any help?

Answer 1

As we don't know what the value of thetax is from your code is it possible you're drawing outside the clipping boundary?

Getting your first drawing up with OpenGL is quite often half of the battle. I would suggest going to DelphiGL and finding an example that is close to what you want and working from there. The site is in German by default, but there's an extensive English translation. In particular they have a useful set of default templates.

Answer 2

I don't know, but while comparing with some opengl code I made long ago:

• I miss defining a viewport with glViewport(0, 0, Width, Height); // Set the viewport for the OpenGL window
• are you sure glortho takes pixel coordinates (instead of opengl relative coordinates?)
• what range is thetax and thetaz?

I also used a different way of setting up dc:

 fdc:=getdc(<windowhandle of control we are displaying on  >);
 FRC := wglCreateContext(FDC);
 b:=wglMakeCurrent(FDC, FRC);

and to finish

 wglMakeCurrent(0, 0); 
 wglDeleteContext(frc);  

Answer 3

Setting up the context correctly is quite hard.

For a re-usable control with decent performance, you'll most likely want a control with it's own DC, but if you can acquire one each time you paint, you might be okay.

Take a look at http://glscene.cvs.sourceforge.net/viewvc/glscene/Source/Platform/GLWin32Viewer.pas?view=log to see how GLScene creates a control that's usable with OpenGL.

The key part in acquiring it's own DC, is overriding the CreateParams procedure + adding:

   with Params do begin
      Style:=Style or WS_CLIPCHILDREN or WS_CLIPSIBLINGS;
      WindowClass.Style:=WindowClass.Style or CS_OWNDC;
   end;

You can then get the DC to use in CreateWnd, and release in DestroyWnd

Once you've got the DC, you'll need to make sure the PixelFormat supports OpenGL + has the details you want:

const pfd: PIXELFORMATDESCRIPTOR = (
    nSize: sizeof(PIXELFORMATDESCRIPTOR);
    nVersion: 1;                       // version
    dwFlags: PFD_DRAW_TO_WINDOW or PFD_SUPPORT_OPENGL or PFD_DOUBLEBUFFER;
    iPixelType: PFD_TYPE_RGBA;
    cColorBits: 24;                    // 24-bit color depth
    cRedBits: 0;
    cRedShift: 0;
    cGreenBits: 0;
    cGreenShift: 0;
    cBlueBits: 0;
    cBlueShift: 0;
    cAlphaBits: 8;                     // alpha bits
    cAlphaShift: 0;
    cAccumBits: 0;                     // accumulation buffer
    cAccumRedBits: 0;
    cAccumGreenBits: 0;
    cAccumBlueBits: 0;
    cAccumAlphaBits: 0;
    cDepthBits: 32;                    // z-buffer
    cStencilBits: 16;                  // stencil buffer
    cAuxBuffers: 0;                    // auxiliary buffer
    iLayerType: PFD_MAIN_PLANE;        // main layer
    bReserved: 0;
    dwLayerMask: 0;
    dwVisibleMask: 0;
    dwDamageMask: 0
);
var
  pf: Integer;
begin
  pf := ChoosePixelFormat(dc, @pfd);
  if not SetPixelFormat(dc, pf, @pfd) then
    Assert(false);//failed, could retry with other settings 
  rc := wglCreateContext(dc);
  if not wglMakeCurrent(dc, rc) then
    Assert(false);// failed
  // we should now have a rc so to test, we'll just clear
  glClearColor(1, 0.5, 0, 1);
  glClear(GL_COLOR_BUFFER_BIT);
  // If we're double-buffered, then swap
  SwapBuffers(dc);
  wglMakeCurrent(0, 0);

After you've finished using the RC, you should also clean up by calling wglDeleteContext.