In addition to the features discussed in DirectDraw, DirectDraw also supports transparent blitting and overlays.
In transparent blitting, a bitmap is transferred to a surface and a certain color, or range of colors, in the bitmap is defined as transparent. Transparent blits are achieved by using color keying. Source color keying operates by defining which color or color range on the bitmap is transparent and therefore not copied during a transfer operation. Destination color keying operates by defining which color or color range on the surface will be covered by pixels of that color or color range in the source bitmap. For more information about color keying, see Color Keying.
Finally, DirectDraw supports overlays in hardware and by software emulation. Overlays present an easier means of implementing sprites and managing multiple layers of animation. Any DirectDrawSurface object can be created as an overlay with all of the capabilities of any other surface, in addition to the extra capabilities associated only with overlays. These capabilities require extra display memory. If there are no overlays in display memory, the overlay surfaces can exist in system memory.
Color keying works in the same way for overlays as for transparent blits. The z-order of the overlay automatically handles the occlusion and transparency manipulations between overlays.