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Graphpac Command Manual	Page 11

Purpose:

To re-activate the graphics format screen.

LOWRES

Graphpac format:

LOWRES

Purpose:

To select the low resolution graphics mode for all subsequent graphics plotting.

HIRES

Graphpac format:

HIRES

Purpose:

To select the high resolution graphics mode for all subsequent graphics plotting.

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 error trapping if required.

WRAP

Graphpac format:

WRAP

Purpose:

To cause subsequent line plotting that leaves the edge of the screen to wrap around and re-enter the screen on the opposite side.

Remarks:

This command together with CLIP are only implemented on systems where the screen resolution allows a wrap around effect to take place.

CLIP

Graphpac format:

CLIP

Purpose:

To disable the wrap around feature of the graphics

Graphpac Command Manual	Page 12

Remarks:

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.

FCON

Graphpac format:

FCON

Purpose:

To enable error trapping when a Graphpac command is asked to act on an X,Y co-ordinate that is not on the screen.

Remarks:

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.

FCOFF

Graphpac format:

FCOFF

Purpose:

To disable error trapping when X,Y co-ordinates that are off the screen are used.

Remarks;

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)

Graphpac format:

SPOKE A,V

Purpose:

To POKE a location inside the video screen memory.

Remarks:

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” is the byte to be POKE’d.