Bf Em
x
Ef
A horizontal position.
Bf Em
y
Ef
A vertical position.
Bf Em
w
Ef
A width.
This function appears to allow setting the video
display rectangle to a sub-rectangle of the
hardware buffer.
Bf Sy
x
Ef
and
Bf Sy
y
Ef
are apparently the
upper left corner, and
Bf Sy
w
Ef
and
Bf Sy
h
Ef
are the width
and height of the rectangle.
It is not clear what should be done if the values
are invalid (negative
Bf Sy
x,
Ef
for example).