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This page uses a turtle-based language called Logo to make simple patterns.
A turtle is a robot which can move a certain distance, and turn through an angle. It is programmed using a language called Logo. The turtle has a pen which draws a line wherever it moves. This pen can be raised or lowered, depending on whether you want the line or not. A real turtle has certain draw-backs. It is rarely accurate, so when you draw a square, it doesn't return to where it started. Also, it's hard to let everyone have their own turtle.
But the turtle concept has certain advantages. It does give a simple introduction to angles, as something that you turn through, rather than the corner of a shape. It also helps people to think of this turn from the point of view of the turtle rather than the onlooker. If the turtle wants to go to the top of the screen and is facing to the left, then it must turn right, but if it is facing to the right, it must turn left. Finally, you program a turtle. This is not a true computer program, as there are no choices. But you can try writing a few instructions, and seeing if they do what you expect!
This page uses a simplified form of Logo, the turtle programming language. It uses entirely buttons and drop-down menus to control an arrow represnting the turtle. If you click on Left 90°, the arrow will do this. If you click on Move 2, the arrow will move 2 squares in the direction that it is facing. As it moves, it colours in the squares that it has left (but not the square that it is on). These are complete squares rather than the line of the original turtle concept, which makes the 45° look a little odd! The initial colour is red, but you can change this. If you click on Pen up, then the arrow becomes a different shade, and will no longer leave a trail behind it. (This is when you want to draw shapes that don't touch.) Pen - none means that the arrow disappears altogether. You can do this at the end of the pattern to get rid of the arrow. It won't let you do anything else until you put the pen in again.
The universe (where the arrow can move) is wrap-round. That means that when you go off one edge, you reappear on the opposite edge.
The arrow starts in the centre. You might prefer to start somewhere else, so there is a drop-down menu to offer some other starting positions. These are starting positions only. If you change this mid-pattern, it will redraw the pattern from the new starting position.
As you click on buttons, you will see the program building up on the right. At any time, you can click on Run Program, and it will rerun the program for you. Only 25 instructions are allowed in the program. You can do more instructions than this, but you won't be able to rerun them - it will only redo the first 25. You can click on Remove last instruction if you decide that you don't like what you've just selected. There is no other way to change the instructions that you have already entered.
Once you think thatyou understand how the instructions work, try selecting Run program when button clicked rather than Run program immediately. This means that nothing happens when you click on Move or Turn buttons, although they get listed in the program. However, when you click on the Run program button, it will run the program, and you will see if it does what you want!
New program cleas everything down to start again.
Click here to try the turtle pattern maker.
© Jo Edkins 2008 - Return to index