Hi!
I'm using Delphi 7.0. I tried to draw on a TPaintBox object but failed. Before trying this I have successfully drawn on TForm and TImage. I cannot find what the problem is. Can you help me to see the code?
Thank you!

This is the simplified code to identify the problem, when I runs the program, it immediately give the error message defined in OnCreate event.

unit testPaintBox1;
interfaceuses Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs, ExtCtrls, OpenGL;
type
TForm1 = class(TForm)
PaintBox1: TPaintBox;
procedure PaintBox1Paint(Sender: TObject);
procedure FormCreate(Sender: TObject);
private
{ Private declarations }
GLContext : HGLRC;
ErrorCode: GLenum;
public
{ Public declarations }
end;
var
Form1: TForm1;
implementation
{$R *.DFM}
procedure TForm1.PaintBox1Paint(Sender: TObject);
begin
ShowMessage('onPaint');
glClear(GL_COLOR_BUFFER_BIT or GL_DEPTH_BUFFER_BIT);
glFlush;
end;

procedure TForm1.FormCreate(Sender: TObject);
var
pfd: TPixelFormatDescriptor;
FormatIndex: integer;
begin
fillchar(pfd,SizeOf(pfd),0);
with pfd do
begin
nSize := SizeOf(pfd);
nVersion := 1; {The current version of the desccriptor is 1}
dwFlags := PFD_DRAW_TO_WINDOW or PFD_SUPPORT_OPENGL;
iPixelType := PFD_TYPE_RGBA;
cColorBits := 24; {support 24-bit color}
cDepthBits := 32; {depth of z-axis}
iLayerType := PFD_MAIN_PLANE;
end; {with}
FormatIndex := ChoosePixelFormat(Form1.PaintBox1.Canvas.Handle,@pfd);
SetPixelFormat(Form1.PaintBox1.Canvas.Handle,FormatIndex,@pfd);
GLContext := wglCreateContext(Form1.PaintBox1.Canvas.Handle);
wglMakeCurrent(Form1.PaintBox1.Canvas.Handle,GLContext);
errorcode:= glGetError;
if errorcode<>GL_NO_ERROR then
ShowMessage('gl error occurs');
end;
end.

Form1.PaintBox1.Canvas.Handle is the problem, cause you have to pass a device context and not the handle of a canvas (that are two totally different things). So you normally have to get a DC from an object via GetDC(Object.Handle), but the TPaintBox-Object has no Handle-Property. So you'll have to go for another object to draw, and I'd suggest you a TPanel instead of a TPaintBox. In the end there is no difference, as you draw GL on it.

_________________
www.SaschaWillems.de | GitHub | Twitter | GPU Datenbanken (Vulkan, GL, GLES)

SOS beliefe it or not, the handle of TCanvas is a DC, but the problem is the same.
TCanvas need a handle of a window to create it's own DC.



If you don't believe SOS, try the following code:

_________________
Danke an alle, die mir (und anderen) geholfen haben.
So weit... ...so gut