GRAPHPAC COMMAND MANUAL Page 5
PENERA or PE
All following DRAW, DRAWTO, DOCAP and PLOT commands will cause any
pixels the CAP passes through to be erased.
PENRET or PR
This allows the CAP to return to the co-ordinates that existed before
the last DRAW, DRAWTO or PLOT commands.
To draw, erase or invert a line based on co-ordinates specified in
The CAP co-ordinates are changed to those specified by X,Y and a line
may be drawn, erased or inverted (depending on the current PEN mode) to these
co-ordinates from the previous CAP. The previous CAP co-ordinates are saved in
case of a following PENRET command.
To draw, erase or invert a line based on relative co-ordinates.
The DRAW command has a similar syntax to the DRAWTO command however
the X,Y values supplied are added to the current CAP co-ordinates to produce a
new CAP. Draw is useful if an object or shape has to be produced several times
but at different screen co-ordinates. The shape is specified by a subroutine
using the DRAW command and whenever the routine is called, the shape will be
produced relative to the current CAP.
GRAPHPAC COMMAND MANUAL Page 6
fo adjust for the height to width ratio of the acreen when using PLOT
or CIRCLE. The argument passed with the RATIO command will be used to modify
the YY axis co-ordinates.
Normally the display on the screen is taller than it is wide and a
circle plotted on the screen would appear oval with the sharp ends in the
vertical plane. RATIO allows the user to introduce a correction factor
whenever PLOT or CIRCLE are used so that a circle does in fact appear as a
circle. RATIO is followed by a single argument. This argument should be in the
range 0 – 511. If 511 is exceeded the value will be MOD 512 (513 will be
treated as 1). A value of 512 (or zero) will cause no correction to take place
and a true (distorted) display will be produced. A value of one will cause
maximum correction to take place and in fact a circle will appear as a single
horizontal line on the screen. The optimum value is somewhere between the two
and should be decided by the user for his particular hardware configuration.
To draw, erase or invert a line based on co-ordinates given in polar
The new CAP co-ordinates are calculated, based on a specified angle
"A" and distance “D". “AY is an angle between 0 and 359 degrees, which is
calculated clockwise, zero degrees being towards the top of the screen. This
value can be exceeded as a wrap around effect takes place, 360 degrees being
the same as 0 degrees, 450 degrees being the same as 90 degrees etc. "D" is a
distance specifying the number of pixels. This distance is modified
automatically by a value dependant on the argument given in a previous RATIO
command and also the value of the angle A. As the argument given in the RATIO
command only modifies calculations in the Y axis, there will be no
modification to the length of lines plotted at angles 90 and 270 degrees,
however as the angle nears the vertical (0 or 180 degrees) the modification
will be at it’s greatest. The old CAP co-ordinates are saved in case of a
following PENRET command.
To draw a circle or are on the screen.
A circle or arc is drawn the centre of which is the CAP and radius is
R. Al and A2 must be positive values with A2 greater than A‘. An are will be
drawn from angle 1 (A!) to angle 2 (A2) in a clockwise direction. If angle 1
is zero and angle 2 is 360 a circle will be drawn. The maximum radius is 511
and if this is exceeded the radius will be MOD $12 as for the distance in the