Opens a GUI to open files. Fully supports the folder system etc.
As of Doors CS 6.4 beta, it uses the new RunProg Chaining system to operate. It puts away any open program before opening a new program, so be aware that pointers in memory might have moved around. It is strongly recommended to re-chkfindsym any RAM (and ROM) variables after calling this function. Note that this function will also move the gui7 AppVar back above any newly-opened files. Doors CS will handle closing any open AP files when your program quits. Note that unlike Doors CS 6.4 beta and lower, Doors CS 6.5 and higher may return pointers to an AP file even if the FileOpen was canceled, ie, the pointers to an already-open file. Nevertheless, it is mandatory that any time FileOpen is called, any open AP file(s) is/are ready to be written back and closed.
a = zero to only show files of the type(s) defined in this AP's header, or nonzero to show all oncalc files
hl = 0 if no file was returned, or the first byte of data if a file was returned
de = pointer to the size word of the data for updating. Please note: the size at the size word is not the same as the size word in bc. bc is 8 bytes smaller than (de) due to the AP header ($BB,$6D,$C9,$31,$80,type,type,type)
bc = size of the pure data section of the file.
If necessary, you should also check hl-3 through hl-1 (3 bytes) to see if it's a valid type for this program.
a, bc, de, hl, Op1, iMathPtrs, GUI Memory Areas