MOVE

Syntax MOVE [#ch,] distance
Location QL ROM

The QL supports a simplified means of drawing pictures known as turtle graphics. This was based upon an early educational tool, whereby simple commands could be entered into a computer to drive a small robot turtle which moved around the floor and held a pen. This pen could either be up in which case the turtle would just move around, or down in which case a line would be left by the turtle on the floor as it moved.

When a window is first opened, an invisible turtle appears at the graphics origin (altered with SCALE) facing to the right, with its pen in the up position.

The command MOVE forces the turtle in the specified window (default #1) to move in the current direction by the specified distance.

The actual distance moved on screen depends on the current SCALE applicable to that window. If distance is negative, the turtle will move backwards. MOVE always works from the current graphics cursor position, and after using this command, the current graphics cursor is placed at the turtle’s position on screen. MOVE is affected by the current INK colour, FILL and also OVER, just like any other graphics command.

Example

A simple procedure to draw a shape of a set number of equal length sides:

100 DEFine PROCedure POLYGON (chan, sides, side_length)
110   TURNTO #chan,0: PENDOWN #chan
120   FOR k = 1 TO sides
130     MOVE #chan, side_length
140     TURN #chan, 360 / sides
150   END FOR k
155   PENUP #chan
160 END DEFine

Try for example, POLYGON #2,5,10.

NOTE

The THOR XVI v6.40 tended to crash when using turtle graphics, especially if a channel number was specified.

CROSS-REFERENCE

PENDOWN forces the pen into the down position, leaving a trail on screen. PENUP allows the turtle to move without leaving a trail. TURN and TURNTO allow you to alter the direction of the turtle.