14.2.6 Remote Desktop Protocol: GDI Acceleration Extension
The Remote Desktop Protocol: Graphics Device Interface (GDI) Acceleration Extension (as specified in [MS-RDPEGDI]) extends the Remote Desktop Protocol: Basic Connectivity and Graphics Remoting (as specified in [MS-RDPBCGR]) by adding advanced drawing-order capabilities and compression techniques. The aim of Remote Desktop Protocol: GDI Acceleration Extension is to reduce the bandwidth associated with graphics remoting by encoding the drawing operations that produce an image instead of encoding the actual image.
For example, instead of sending the bitmap image of a filled rectangle from server to client, an order to render a rectangle at coordinate (X, Y) with a given width, height, and fill color is sent to the client. The client then executes the drawing order to produce the intended graphics result.
In addition to defining how to encode common drawing operations, the Remote Desktop Protocol: GDI Acceleration Extension also facilitates the use of caches to store drawing primitives such as bitmaps, color tables, and characters. The effective use of caching techniques helps to reduce wire traffic by ensuring that items used in multiple drawing operations are sent only once from server to client (retransmission of these items for use in conjunction with future drawing operations is not required once the item has been cached on the client).