80-Bus News

Graphpac Command Manual	Page 7

It is possible to place the CAP on the circumference of a circle after it has been drawn by using the PLOT command, with the circle radius given as the plot distance. Obviously the same RATIO value must be used for the PLOT and CIRCLE commands for the result to be correct.

DOCAP

Graphpac format:

DOCAP

Purpose:

To alter a single pixel at the CAP co-ordinates dependent on the current PEN mode.

Example:

The following is a BASIC program that follows the actions taken by the CIRCLE command. Execution is slower as the CIRCLE command is a machine code subroutine and does not involve any of the overheads associated with a BASIC program.

10 STARTAT X,Y : REM THE MIDDLE OF THE SCREEN
20 FOR A=0 TO 360
30 PENUP
40 PLOT A,R : REM RIS THE RADIUS OF THE CIRCLE
50 PENDOWN : DOCAP : PENRET
60 NEXT A

CAP

Graphpac format:

CAP

Purpose:

The CAP command has been added to assist the programmer. It reports the CAP co-ordinates, allowing a programs action to be investigated.

Remarks:

CAP reports the co-ordinates on the screen at the current cursor location in much the same way as a normal print statement.

CAP‰

Graphpac format:

CAP‰ CC,RR

Purpose:

CAP‰ CC,RR reports the co-ordinates on the screen at the specified CC,RR screen co-ordinates. This action does not effect the cursor address so that subsequent print statements will act correctly.

LCAP

Graphpac format:

LCAP

Graphpac Command Manual	Page 8

Purpose:

This reports the CAP co-ordinates on a printer allowing a program’s action to be investigated.

Remarks:

LCAP will report the CAP co-ordinates to a printer (or the current LST: device if running under CP/M).

CLS

Graphpac format:

CLS

Purpose:

To clear the screen of all graphics and alpha-numeric characters.

GCLR (Graphics Clear)

Graphpac format:

GCLR

Purpose:

To clear the screen of graphic characters.

Remarks:

A search is made in the screen memory for any graphic characters. If any are found they are replaced with a space character. (20 hex.)

CLEOL (CLear To End Of Line)

Graphpac format:

CLEOL

Purpose:

To clear the display from the current cursor position to the end of the current line.

SCROLL

Graphpac format:

SCROLL n

Purpose:

To cause scrolling to affect a number of lines (n) on the video display.

Remarks:

The number of lines specified in the scroll command will be situated at the bottom of the screen, allowing a display area above to be fixed for graphics plotting. Alpha-numerics can still be used on the display area with the use of the SCREEN command. If it is wished to return scrolling to normal, use the command SCROLL 25. Scrolling will only take place on receipt of a line feed while the cursor is on the bottom line of the display.