Updating an SDL/OpenGL context...

sealfin

Moderator

Posts: 675
Joined: 2002.04

Post: #1

Sep 10, 2003 — 05:05 AM

...or, "how are you supposed to?"
At the moment, the context is only update if it receives an external event (ie. resizing the context) - I've tried to force it to update by SDL_UnlockSurface followed by SDL_UpdateRect, but this merely crashes the app... any suggestions?

Mark Bishop

sealfin

Moderator

Posts: 675
Joined: 2002.04

Post: #2

Sep 10, 2003 — 05:08 AM

The source might be helpful...

Code:

int main(int argc,

         char *argv[])

{

  SDL_Surface  *theSurface;

  SDL_Event       theEvent;

  const Uint32 theInitialisationFlags = ( SDL_INIT_VIDEO ),

               theVideoFlags = ( SDL_OPENGL );

  const Uint16 theWidth = 640,

               theHeight = 480;

  const Uint8  theDepth = 16;

  Uint8           whetherFullscreen = false;

  if( SDL_Init( theInitialisationFlags ) != 0 )

    goto label_quit;

  if(( SDL_GL_SetAttribute( SDL_GL_DOUBLEBUFFER, 1 ) != 0 )

  || ( SDL_GL_SetAttribute( SDL_GL_DEPTH_SIZE, 16 ) != 0 )

  || ( SDL_GL_SetAttribute( SDL_GL_RED_SIZE, 5 ) != 0 )

  || ( SDL_GL_SetAttribute( SDL_GL_GREEN_SIZE, 5 ) != 0 )

  || ( SDL_GL_SetAttribute( SDL_GL_BLUE_SIZE, 5 ) != 0 ))

    goto label_quit;

  label_video_initialisation:

  if(( theSurface = SDL_SetVideoMode( theWidth, theHeight, theDepth, ( theVideoFlags | ( SDL_FULLSCREEN * whetherFullscreen )))) == NULL )

    goto label_quit;

    //    Sets the fill-colour to a RGBA colour, and fills the context with that colour.

  glClearColor(0.30, 0.38, 0.60, 1.0);

  glClear(GL_COLOR_BUFFER_BIT);

    //    The context is not updated until the 'glFinish()'.

  glFinish();

    //    we like to crash you...

  SDL_UnlockSurface( theSurface );

  SDL_UpdateRect( theSurface, 0, 0, 0, 0 );

    //

  label_loop:

  while( SDL_PollEvent( &theEvent ))

    if( theEvent.type == SDL_KEYDOWN )

      switch( theEvent.key.keysym.sym )

      {

        case SDLK_ESCAPE:

          goto label_quit;

        case SDLK_f:

          whetherFullscreen ^= true;

          SDL_FreeSurface( theSurface );

          goto label_video_initialisation;

        default:;

      }

  goto label_loop;

  label_quit:

  SDL_Quit();

  return 0;

}

Yes, I know, lots of labels, bad bad sealfin...

Mark Bishop

sealfin

Moderator

Posts: 675
Joined: 2002.04

Post: #3

Sep 10, 2003 — 06:13 AM

Found the error - a slight oversight, I'd created a double buffered context, but never swapped the buffers...

Mark Bishop

Possibly Related Threads...

Thread:		Author	Replies:	Views:	Last Post
	Full screen context doesn't remain the current context	Malarkey	3	2,966	Feb 1, 2007 05:27 PM Last Post: OneSadCookie
	cocoa for nibbies [OpenGL context creation/ Initializing a PixelFormat]	Byron Clarke	7	3,565	Jun 23, 2005 01:23 AM Last Post: Byron Clarke
	Screenshot of OpenGL context	aarku	6	6,328	Jul 23, 2004 07:05 PM Last Post: aarku
	Placing Quesa Objects in an OpenGL Context?	lpetrich	2	2,484	Feb 13, 2003 06:53 AM Last Post: -dair
	OpenGL context and Windows/Dialogs	oxenos	4	3,064	Dec 30, 2002 06:25 AM Last Post: oxenos