Beginner has trouble with SDL in foll-screen mode.

[Hendrik Boom <hendrik@topoi.pooq.com>]

I have a small program that makes a time-varying pattern on the
screen. It works fine with SDL_RESIZABLE, but not with SDL_FULLSCREEN.

In full-screen mode everything is sheared off into wavy lines, as if the
screen geometry I'm using is not the actual one.

Now I understand that it may be unable to deliver the desired resolution,
but if so SDL_SetVideoMode should be returning error indication,
right?

Although I don't get an error return, i called SDL_GetError anyway and got
the following message:

  Failed loading DPMSDisable: /usr/lib/libX11.so.6: undefined symbol:    DPMSDisable
 
I don't know if that means anything important, because it happens
both with SDL_FULLSCREEN and with SDL_RESIZABLE.

Here's the code.  The #if is how I switch between full-screen and
resizable.  Am I doing something obviously wrong?


#include <SDL/SDL.h>
#include <stdio.h>
#include <stdlib.h>

Uint16 CreateHicolorPixel(
			  SDL_PixelFormat * fmt,
			  Uint8 red,
			  Uint8 green,
			  Uint8 blue)
{
  Uint16 value;
  value = ((red >> fmt->Rloss) << fmt->Rshift) +
    ((green >> fmt->Gloss) << fmt->Gshift) +
    ((blue >> fmt->Bloss) << fmt->Bshift);
  return value;
}

int main()
{
  SDL_Surface *screen;
  Uint16 *raw_pixels;
  int x, y, t;

  printf("At start GetError says: %s\n", SDL_GetError());
  if(SDL_Init(SDL_INIT_VIDEO) != 0)
    {
      printf("unable to initialize SDL: %s\n", SDL_GetError());
      return 1;
    }
  atexit(SDL_Quit);

  printf("After SDL_INIT GetError says: %s\n", SDL_GetError());
#if 1
  screen = SDL_SetVideoMode(640, 480, 16, SDL_FULLSCREEN);
#else
  screen = SDL_SetVideoMode(640, 480, 16, SDL_RESIZABLE);
#endif

      printf("after SetVideoMods GetError says: %s\n", SDL_GetError());
  if(screen == NULL)
    {
      printf("unable to set video mode: %s\n", SDL_GetError());
      return 1;
    }

  for(t = 0; t < 20; ++t)
    {
      SDL_LockSurface(screen);
      raw_pixels = (Uint16 *) screen->pixels;
      for(x = 0; x < screen->w; x++)
	{
	  for(y = 0; y < screen->h; y++)
	    {
	      Uint16 pixel_color;
	      int offset;
	      pixel_color = CreateHicolorPixel(screen->format,
					       (x * t) >> 4,
					       (x ^ y) + t,
					       (y * t) >> 4

					       );
	      offset = (screen->pitch / 2 * y + x);
	      raw_pixels[offset] = pixel_color;
	    }
	}
      SDL_UnlockSurface(screen);
      SDL_UpdateRect(screen, 0, 0, 0, 0);
      SDL_Delay(8);
    }

  SDL_Delay(3000);
  printf("success!\n");
  return 0;
}