GRAPHPAC COMMAND MANUAL Page 11
To re-activate the graphics format screen.
To select the low resolution graphics mode for all subsequent graphics
To select the high resolution graphics
mode for all sub
graphics plotting. ubsequent
Line clipping and error trapping.
On systems where it has been possible to implement a wrap around
affect, the commands WRAP and CLIP have been included (to enable the wrap
around affect or clip lines at the edge of the screen respectively). As an
alternative where this has not been possible the commands, FCON and FCOFF have
been implemented so that the user has the choice of
vequired of error trapping if
To cause subsequent line plotting that leaves the edge of the
to wrap around and re-enter the screen on the opposite side. 8
This command together with CLIP are only implemented on systems where
the screen resolution allows a wrap around effect to take place.
To disable the wrap around feature of the graphics
GRAPHPAC COMMAND MANUAL Page 12
Lines that leave the screen in any direction are clipped and do not
re-appear on the opposite side of the screen. Any graphic statement that
attempts to act on an X,Y co-ordinate outside the. specified screen range will
have no effect, however the CAP will still be updated. This command disables
the wrap around effect caused by WRAP. It should be noted that CLIP only acts
on PLOT,DRAW, DRAWTO and CIRCLE commands, normal pixel control using
PSET,PRESET and PTEST will always act on the screen the wrap around feature
always being operational.
To enable error trapping when a Graphpac command is asked to act on an
X,Y co-ordinate that ig not on the screen.
After FCON has been executed any attempt to use X,Y co-ordinates that
are not on the screen will cause an illegal function call error. FCON is
active when the package is first executed.
To disable error trapping when X,Y co-ordinates that are off the
screen are used.
Graphpac commands which are called to act on X,Y co-ordinates that are
off the screen may be executed. No physical change to the screen contents will
occur however, the CAP will be updated where applicable.
SPOKE (Screen POKE)
To POKE a location inside the video screen memory.
Where the design of the hardware causes the video memory to be outside
the normal Z80 64K memory map, SPOKE has been implemented. The normal BASIC
POKE statement cannot reach the video RAM. SPOKE has been included to give
this facility. The syntax is the same as the POKE statement. “A” represents a
location in the video memory, the value represents an offset (in characters)
from the start of the display. “v” ia the byte to be POKE’d.