簡単なプログラムです。(動作未検証)
ACLS
VAR APPWPOS[2,4]
APPWPOS[0,0] = 200
APPWPOS[0,1] = 100
APPWPOS[0,2] = 100
APPWPOS[0,3] = 100
WHILE TRUE
GCLS
GBOX APPWPOS[0,0]-1,APPWPOS[0,1]-1,APPWPOS[0,0]+APPWPOS[0,2]+1,APPWPOS[0,1]+APPWPOS[0,3]+1,#BLACK
GFILL APPWPOS[0,0],APPWPOS[0,1],APPWPOS[0,0]+APPWPOS[0,2],APPWPOS[0,1]+APPWPOS[0,3],#WHITE
VSYNC 1
WEND