## Display Device Driver Reference for OS/2

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### New Background Mix Support

The background mix, BM_SRCTRANSPARENT, is used in calls to GpiBitBlt and GpiDrawBits so that pels in a source bit map that match pels in the target presentation space background color are not copied to the output bit map. Where source bit-map pels match the background color, target bit-map pels are left unchanged, which provides a transparent overlay function.

The background mix, BM_DESTTRANSPARENT, also is used in calls to GpiBitBlt and GpiDrawBits, to permit pels from the source bit map to be copied to only the target pels that match the background color of the presentation space. Pels in the target are changed where the source bit-map pels match the background color of the target, thus providing a transparent underlay function.