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Written By Ian S. Gibson


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Game Screenshot

Turtles

Ian S. Gibson, Maidstone, Kent

This program enables the BBC B or Electron to perform several features associated with Turtle graphics. When you run the program, the micro's name appears with a prompt. Electron users should change Mode 7 statement to Mode 6 when typing in. The following commands are available in memory from the start. They can be used to build up other user-defined words. These resident words are as follows:

Word Abbreviation Meaning
Circle C Draws a circle, centre graphics cursor, radius R. F is 0 for unfilled, 1 for filled.
Fill - Fill area of screen above and below graphics cursor.
Left X L Rotate cursor X degrees left - anti-clockwise.
Right X R Rotate X degrees right - clockwise.
Forward X F Draw line forward X units.
Pencil X P Change colour of graphics, 0-3
Clean - Clear the screen.
Save X$ - Save all user-defined words under the name, X$
Load X$ - Load program marked X$
New - Erases all user-defined words.
Move X - Move cursor forward X units without drawing.
Plot - Plot cursor position.
Home - Return cursor to bottom left-hand corner.
Colour XY - Change logical colour X to actual colour Y.
Wait X - Pause for X units.
Triangle X T Make a triangle; the third point is X units ahead, and the other two are the last two points plotted or moved to.
Scale X - Changes the scale of future drawing - 1 is default.
Dot - Makes future lines dotted.
Line - Makes future lines undotted.
Forget X$ - Forgets the user defined word, X$
Text X$ - Writes text at graphics cursor.

The following commands may not be used in user-defined words.

List - Lists all user-defined words
Goodbye Bye Returns to Basic.
Build X$ B Creates or edits a user-defined word with the name X$.

Save Completed Picture

To save a completed picture without the user-defined words, type Bye and RETURN followed by:

*SAVE "name" 5800 7FFF

and re-loading by:

*LOAD "name"

To create a user-defined word, X$, the following procedure should be used.

BUILD X$ - where X$ is a name.

Select a line number 1-20.

The contents of that line may be any user-defined, or resident word in Turtle's dictionary, for example F 100. In addition, after selecting a line number, Insert F0 or Delete F9 are available. Insert moves all lines after and including the selected line up one place. Line 20 is lost. Delete deletes the selected line thus moving all subsequent lines down one place. Return exits the editor when used instead of a line number.

Here is an example of a user-defined word:

BUILD STEP
1 (RETURN)
FORWARD 50 (RETURN)
2 (RETURN)
RIGHT 90 (RETURN)
3 (RETURN)
FORWARD 50 (RETURN)
4 (RETURN)
LEFT 90 (RETURN) (RETURN)

Type:

HOME (RETURN)
STEP (RETURN)

should produce a step.

User-Defined Words Repeated

User-defined words can be repeated by putting a number after them. For example Step 5 and RETURN produces five more steps. Once a word has been defined, it may be used in any other user-defined word. For example:

BUILD STEPS (RETURN)
1 (RETURN)
HOME (RETURN)
2 (RETURN)
STEP 5 (RETURN) (RETURN)
STEPS (RETURN)

produces five steps.

Complex patterns can be built up in this way very easily. Programs may be merged simply by loading and running two sets of saved words to produce a final picture.