Bitmap

A bitmap is a two-color image where each bit in the image determines which of two specified colors appears on the screen.

opaque bitmap

a bitmap that is expanded to a specified foreground color for each set bit and a background color for each clear bit in a bitmap.

transparent bitmap

a bitmap that is expanded to a foreground color pixel for a set bit and no pixel drawn or modified for a clear bit.

The X Window interface requires support for both opaque and transparent bitmaps. X requires that, after each bit is expanded to a full pixel depth, the raster op mix (alu) occur with the destination pixel and that the hardware planemask be applied to the result when the destination pixel is written.

Most recent graphics chips can achieve all these tasks. Exceptions to this are the Weitek P9000 that cannot apply a raster operation to a transparent expanded pixel and the Cirrus GD5426 which does not support a planemask.

The NFB interface supports the following routines to manipulate bitmaps:

Routine	Description
DrawMonoImage(D3nfb)	draws transparent bitmaps
DrawOpaqueMonoImage(D3nfb)	draws opaque expanded bitmaps