Still image (single frame) or how to stop opengl?
lazarus / 39-Graphics

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Peiman · 2011-07-13 20:57

Hi,

Opengl refreshes the scene automatically by a certain FPS. I wonder if
it is possible to render just one frame. Is there any function to stop
its working? I even used destroy destructor. though rendering stopped
but the cpu usage remained high until I stopped the main application.

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Leledumbo · 2011-07-14 04:44

QuoteOpengl refreshes the scene automatically by a certain FPSAre you
sure? Coz in my app, the main loop does it. And without, the scene
doesn't get refreshed at all. Would you mind showing some code?

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Peiman · 2011-07-14 06:01

This is the code,
TT and C are depth-sorted arrays of triangles and their respective
colors.
I used the bool variable Q to assure only once the paint is done and
on the second time it destroys the openglcontrol1. After calling the
destroy method, it does not render any more, but the cpu core #4 keeps
its 40% performance.

urender, geotypes and geofunc are my units for geometrical
calculations

Code: [Select]uses
  Classes, Windows,SysUtils, LCLProc, LResources, Forms, Controls,
Graphics, Dialogs,
  OpenGLContext, GL, GLU, urender, geotypes, geofunc;

type

  { TForm1 }

  TForm1 = class(TForm)
    procedure FormCreate(Sender: TObject);
    procedure OpenGLControl1Paint(Sender: TObject);
  private
  public
    OpenGLControl1: TOpenGLControl;
  end;

var
  Form1: TForm1;
  Q : boolean = true;
implementation

{$R *.lfm}



{ TForm1 }

procedure TForm1.FormCreate(Sender: TObject);
begin

  OpenGLControl1:=TOpenGLControl.Create(form1);
  with OpenGLControl1 do begin
    Name:='OpenGLControl1';
    Align:=alClient;
    Parent:=Self;
    OnPaint:=@OpenGLControl1Paint;
    AutoResizeViewport:=true;
  end;
end;

procedure TForm1.OpenGLControl1Paint(Sender: TObject);
var
  i,j,N : integer;
  r : single;
begin
if Q then
  begin
  glClearColor(1.0, 1.0, 1.0, 1.0);
  glClear(GL_COLOR_BUFFER_BIT);
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  gluPerspective(45.0, double(width) / height, 0.1, 100.0);
  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();
  gluLookAt(5,5,5,0,0,0,0,1,0);
  glEnable(GL_BLEND);
  glBlendFunc (GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA);


// opengl geometry
  n := 10;
  for i := 0 to n-1 do
    begin
    glBegin(GL_TRIANGLES);
    glColor4f(C[i].x,C[i].y,C[i].z,0.15);
      for j := 0 to 2 do
        glVertex3f( TT[i,j].x, TT[i,j].y, TT[i,j].z); 
    glEnd();
    end;

  OpenGLControl1.SwapBuffers;
  Q := not(Q);
  end
else
  OpenGLControl1.destroy;
end;

end.

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User137 · 2011-07-15 00:52

You shouldn't need to call .Destroy at all. TForm frees all its child
components automatically when program ends, such as TButton, TPanel...
and TOpenGLControl, one of which you assigned to form1.

Anyway, it also looks weird code for 2 reasons:
1) You are calling OpenGLControl1.destroy instead of
OpenGLControl1.free (or rather better FreeAndNil(OpenGLControl1) ).
You should never call .Destroy directly... I do not know the
difference exactly but that is basic.

2) Also destroying an object from within the object itself. Imagine
this kind of internal code flow:
Code: [Select]procedure TOpenGLControl.HandleEvents
begin
  ...
  case Event of
    event_Paint:
      DoPaint(self); // <-- Here would be called OpenGLControl1Paint()
        // from which you are destroying this object, and propably
this whole code block that calls it
    ...
  end;
  ...
  DoSomethingElse; // Now if the object is destroyed, everything
happening here
    // would be undefined and prone to Access violation
end;

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Leledumbo · 2011-07-15 04:36

Instead of having Q, you can simple assign nil to OnPaint of
OpenGLControl1. I have no idea which code takes 40% cpu, I'll try
debugging your code tonight.