J'ai initialise directdraw avec cette fonction:

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static int
_directdraw_init (HWND                 window,
		  LPDIRECTDRAW        *object,
		  LPDIRECTDRAWSURFACE *surface_primary,
		  LPDIRECTDRAWSURFACE *surface_back,
		  int                 *depth,
		  int width,
		  int height)
{
   DDSURFACEDESC2      surface_desc;
   DDPIXELFORMAT       pixel_format;
   LPDIRECTDRAWCLIPPER clipper;
   LPDIRECTDRAW        o;
   DDSURFACEDESC2     *sd;
   HRESULT             res;

   res = DirectDrawCreateEx (NULL, (void **)&o, &IID_IDirectDraw7, NULL);
   if (FAILED(res))
     return 0;

   res = IDirectDraw7_SetCooperativeLevel (o, window, DDSCL_NORMAL);
   if (FAILED(res))
     {
	IDirectDraw7_Release (o);
	return 0;
     }

   res = IDirectDraw7_CreateClipper (o, 0, &clipper, NULL);
   if (FAILED(res))
     {
	IDirectDraw7_Release (o);
	return 0;
     }

   res = IDirectDrawClipper_SetHWnd (clipper, 0, window);
   if (FAILED(res))
     {
	IDirectDrawClipper_Release (clipper);
	IDirectDraw7_Release (o);
	return 0;
     }

   memset(&surface_desc, 0, sizeof(surface_desc));
   surface_desc.dwSize = sizeof(surface_desc);
   surface_desc.dwFlags = DDSD_CAPS;
   surface_desc.ddsCaps.dwCaps = DDSCAPS_PRIMARYSURFACE;

   sd=&surface_desc;
   res = IDirectDraw7_CreateSurface (o, &surface_desc,
				     surface_primary, NULL);
   if (FAILED(res))
     {
	IDirectDrawClipper_Release (clipper);
	IDirectDraw7_Release (o);
	return 0;
     }

   res = IDirectDrawSurface7_SetClipper (*surface_primary, clipper);
   if (FAILED(res))
     {
	IDirectDrawClipper_Release (clipper);
	IDirectDrawSurface7_Release (*surface_primary);
	IDirectDraw7_Release (o);
	return 0;
     }

   memset (&surface_desc, 0, sizeof(surface_desc));
   surface_desc.dwSize = sizeof(surface_desc);
   surface_desc.dwFlags = DDSD_CAPS | DDSD_HEIGHT | DDSD_WIDTH;
   surface_desc.ddsCaps.dwCaps = DDSCAPS_OFFSCREENPLAIN;
   surface_desc.dwWidth = width;
   surface_desc.dwHeight = height;

   sd=&surface_desc;
   res = IDirectDraw7_CreateSurface (o, (DDSURFACEDESC *)sd,
				     surface_back, NULL);
   if (FAILED(res))
     {
	IDirectDrawClipper_Release (clipper);
	IDirectDrawSurface7_Release (*surface_primary);
	IDirectDraw7_Release (o);
	return 0;
     }

   ZeroMemory(&pixel_format, sizeof(pixel_format));
   pixel_format.dwSize = sizeof(pixel_format);
   IDirectDrawSurface7_GetPixelFormat(*surface_primary, &pixel_format);

   *object = o;
   *depth = pixel_format.dwRGBBitCount;

   return 1;
}
j'ai mis mon affichage en 16 bits, et cree une surface de taille 400x400 (width et height dans la fonction ci-dessus).

A priori, le pitch devrait etre de width * depth / 8, ou depth est le nombre de bits de l'affichage. Donc le pitch devrait etre de 800.

Mais quand j'affiche la valeur de surface_desc->lPitch, ou surface_desc est la description de ma surface, j'obtiens 832.

quelqu'un voit-il pourquoi ?

merci