How to access OpenGL rendering context on Android with Delphi XE5?

Question

How to create OpenGL rendering context on Android device when developing an application with Delphi XE5?

Basically I don't know where to start. There are no OpenGL examples yet.

What I would expect to exist:

• Some kind of event (Panel.OnRender) that would provide an existing context in which I could call OpenGL calls.

• Generic TOpenGLSurface control that could be placed in forms designer

• A way to create context on main form in runtime.

From my research so far I that TWindowManager.Render has access to OpenGL calls and uses them to render popup windows.

EDIT: Adding a Timer to a form and calling this procedure fills the screen with green, so that means GL context is already there:

procedure TForm1.Timer1Timer(Sender: TObject);
begin
  glClearColor(0, 1, 0, 0);
  glClear(GL_DEPTH_BUFFER_BIT or GL_STENCIL_BUFFER_BIT or GL_COLOR_BUFFER_BIT);
  eglSwapBuffers(TCustomAndroidContext.SharedDisplay, TCustomAndroidContext.SharedSurface);
end;

The question is - how to properly handle it, cos rendering on Timer in controlled environment is definitely a bad idea.

Answer 1

I'm going to append to this answer as new details reveal.

Attempt 1

Adding a Timer to a form and calling this procedure fills the screen with green, so that means GL context is already there:

procedure TForm1.Timer1Timer(Sender: TObject);
begin
  glClearColor(0, 1, 0, 0);
  glClear(GL_DEPTH_BUFFER_BIT or GL_STENCIL_BUFFER_BIT or GL_COLOR_BUFFER_BIT);
  eglSwapBuffers(TCustomAndroidContext.SharedDisplay, TCustomAndroidContext.SharedSurface);
end;

Of course rendering on Timer in controlled environment is definitely a bad idea. The app kept on flickering on minimize/maximize.

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Attempt 2

I have overridden TContextAndroid class (made a copy of Delphi unit and placed it into my app folder). I was able to inject custom code into DoEndScene method and it has successfully executed it - for this test just a simple glClear(GL_COLOR_BUFFER_BIT);. This has filled the entire application area with color. This time the application did not flickered and behaved just like normal.

---

Attempt 3

Here's the code that made it to work and that does not looks hacky:

types
  TMyForm = class(TForm3D)
    procedure Form3DRender(Sender: TObject; Context: TContext3D);
  end;

implementation

//Event handler for TForm.OnRender
procedure TMyForm.Form3DRender(Sender: TObject; Context: TContext3D);
begin
  glClearColor(1, 1, 0, 1);
  glClear(GL_COLOR_BUFFER_BIT);
end;