Ok, I can do writing text to the screen and drawing lines in Business Basic.

The y coordinate is zero in the lower left.

emu.keypost doesn't work correctly, I get @ instead of ".

Code
emu.keypost([[
INVOKE "BGRAF.INV"
PERFORM GRAFIXMODE (%2,%1)  : REM 2 IS 560X192 B/W
PERFORM INITGRAFIX
PERFORM FILLCOLOR (%0)
PERFORM FILLPORT            : REM ERASE TO COLOR 0
PERFORM GRAFIXON
OPEN #1,".grafix"
FOR Y=0 TO 190 STEP 10
PERFORM MOVETO(%0,%0)
PERFORM LINETO(%320,%Y)
PRINT #1;"X,Y=(";EXFN%.XLOC:",";EXFN%.YLOC;")"
NEXT Y
]])

[Linked Image from i.imgur.com]
[Linked Image from i.imgur.com]