3.1.1.1.5 Offscreen Bitmap Cache

The Offscreen Bitmap Cache is used to store writable offscreen bitmap surfaces. There is only one cache for all offscreen bitmaps. The bitmap sizes are variable and depend on the dimensions specified by the Create Offscreen Bitmap (section 2.2.2.2.1.3.2) Alternate Secondary Drawing Order.

The total cache size and cache entries are capped by the values specified in the Offscreen Bitmap Cache Capability Set (see [MS-RDPBCGR] section 2.2.7.1.9). The default size of the cache is 2.5 MB for 8 bpp, 5 MB for 16 bpp, or 7.5 MB for 24 bpp. The default number of allowed cache entries is 100.

The Create Offscreen Bitmap (section 2.2.2.2.1.3.2) and Switch Surface (section 2.2.2.2.1.3.3) Alternate Secondary Drawing Orders are used to manipulate the offscreen cache. Images stored in the Offscreen Bitmap Cache are rendered with the MemBlt (section 2.2.2.2.1.1.2.9) and Mem3Blt (section 2.2.2.2.1.1.2.10) Primary Drawing Orders.