The SetSwapDrive function uses the current swap drive and path.
BL
Specifies the ASCII drive letter for the swap drive (such as A, B, or C). This register contains 0FFh if no swap drive is available.
DS
Specifies the segment address of the grabber (CS and DS registers are equal).
ES:DI
Points to the path template for Windows temporary-file format.
This function has no return value.
The next call to the following SaveScreen function uses the given swap drive letter to open the swap file, if needed. Failure to call this function at least once before SaveScreen may result in a failure to switch the video context. This drive and path information is stored as a static value and need not be set before every call to SaveScreen.