INFO: Differences Between Full Screen and Windowed Mode Palettes (140588)

SUMMARY

You can use the Game SDK function CreatePalette() to create a DIRECTDRAWPALETTE object for a DirectDraw object.

When in full screen mode, you have control over the complete physical palette except for the first and last colors, black and white. When in full screen mode, the first and last entries of the palette will be set to black and white no matter what the user has specified for these entries.

You can over-ride this feature by specifying DDPCAPS_ALLOW256 in the flags field for the CreatePalette() call. This flag should be used with caution. On some video cards, setting palette entry 0 to a color other than black could change the color of the overscan region, the area of the display tube outside of the normal video display. When you are running in windowed mode (DDSCL_NORMAL), you will not be able to change the first and last 10 colors of the physical palette. This means that when your application goes between the full screen and windowed modes, you need to change the bits of your bitmap data before you will be able to display them properly.

MORE INFORMATION

Use the following code to create a gray-scale palette with 256 colors:

   for( i=0; i<256; i++ )

   {
   ape[i].peRed   = (BYTE)i;
   ape[i].peGreen = (BYTE)i;
   ape[i].peBlue  = (BYTE)i;
   ape[i].peFlags = 0;
   }

   ddrval = IDirectDraw_CreatePalette(lpDD, DDPCAPS_8BIT, ape,

                                      &ppal, NULL);

Now, when in full screen mode, all 256 colors will be set -- the larger the palette index number, the brighter the color. All of your offscreen surfaces (bitmaps) will contain bytes that map to these 256 colors correctly.

However, when you go into windowed mode, your bitmaps will no longer map to the colors correctly because the 256 palette entries you specified in "ape" are mapped to the physical palette like a GDI logical palette is mapped to the physical palette when RealizePalette() is called.

In windowed mode, there is no way to know how your 256 colors will get mapped unless you use the PC_NOCOLLAPSE flag for your entries. This way, you can ensure that entry 1 will map to physical entry 10, entry 2 will map to physical entry 11, entry 3 will map to physical entry 12, and so on. You should rely only on the first 236 colors, though, because there are only 236 free entries in the physical palette when in windowed mode.

For example, you could call the following code when your application switches to windowed mode:

   for( i=0; i<256; i++ )

   {
   ape[i].peRed   = (BYTE)i;
   ape[i].peGreen = (BYTE)i;
   ape[i].peBlue  = (BYTE)i;
   ape[i].peFlags = PC_NOCOLLAPSE;
   }

   ddrval = IDirectDraw_CreatePalette(lpDD, DDPCAPS_8BIT, ape,

                                      &ppal, NULL);

Now you need to add 10 to all of the bytes in all of your bitmap data because all colors are now offset by 10. Once you have done so, your bitmap images will display correctly.