The DirectDraw object represents the display device. There can be one DirectDraw object for every logical display device in operation. An application development environment, for instance, might have two monitors, one running the application using DirectDraw and one running the development environment using GDI.
A DirectDrawSurface object represents a linear region of display memory that can be directly accessed and manipulated. These display memory addresses may point to visible frame buffer memory (primary surface) or to non-visible buffers (off-screen or overlay surfaces). These non-visible buffers usually reside in display memory, but can be created in system memory if required by the hardware design or if DirectDraw is doing software emulation. An overlay is a surface that can be made visible without altering the pixels it is obscuring. Overlays and sprites are synonymous. A texture map is a surface that can be wrapped onto a 3D surface.
A DirectDrawPalette object represents either a 16 or a 256 color-indexed palette. Palettes are provided for textures, off-screen surfaces, and overlay surfaces, none of which are required to have the same palette as the primary surface.
The DirectDraw object creates DirectDrawSurface, DirectDrawPalette, and DirectDrawClipper objects. DirectDrawPalette and DirectDrawClipper objects must be attached to the DirectDrawSurface objects they affect. A DirectDrawSurface may refuse the request to attach a DirectDrawPalette to it. This is not unusual because most hardware does not support multiple palettes.