## Display Device Driver Reference for OS/2

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### PixBltThroughClipsViaPhunk (PIXBLT.C) and PixBltThroughClips (PIXBLT.C)

PixBltThroughClipsViaPhunk and PixBltThroughClips have similar functions. Both enumerate through the clipping rectangles passed in from the graphics engine (GRE), batch up a number of them, and then call the blt function specified in SPad.BltFunction with those rectangles. This process is repeated until all clipping rectangles have been exhausted. The two differ in that PixBltThroughClips is designed to deal with bit maps that are either both in VRAM, or both in system memory. PixBltThroughClipsViaPhunk is used when the source is in system memory and the destination is in video memory. PixBltThroughClipsViaPhunk is also used when the source is in video memory and the destination is system memory. If the source and destination are both in system memory, only PixBltThroughClips is called. Likewise, if the source and destination of the blt are in video memory, only PixBltThroughClips needs to be called. There is one special case. In PixbltThroughClipsViaPhunk, if the source is in system memory and the destination is video memory, it is possible that the source might fit into bit map cache. If the source will fit, PixBltThroughClipsViaPhunk copies the source into the cache. Once the source has been cached, both the source and the destination are in video memory. This means that PixBltThroughClipsViaPhunk can call PixBltThroughClips to perform the blt.

If the source bit map will not fit in the cache, PixBltThroughClipsViaPhunk copies the source bit map into the Phunk in 64KB chunks. It calls CopyChunkToPhunkForPixBltSource to put the source into the Phunk. CopyChunkToPhunkForPixBltSource uses eddf_MESS to copy a portion of the source bit map into the Phunk. For the XGA, this allowed the bit map to be blted to VRAM by way of the bus-master. For the S3 chip, the Phunk is just another 64KB of system memory. PixBltThroughClipsViaPhunk is used when the source is in system memory and the destination is in video memory. PixBltThroughClipsViaPhunk is also used when the source is in video memory and the destination is system memory. If the source and destination are both in system memory, only PixBltThroughClips is called. Likewise, if the source and destination of the blt are in video memory, only PixBltThroughClips needs to be called. There is one special case. In PixbltThroughClipsViaPhunk, if the source is in system memory and the destination is video memory, it is possible that the source might fit into bit map cache. If the source will fit, PixBltThroughClipsViaPhunk copies the source into the cache. Once the source has been cached, both the source and the destination are in video memory. This means that PixBltThroughClipsViaPhunk can call PixBltThroughClips to perform the blt.