1 building your own turtle functions for making really cool pictures!
Post on 13-Jan-2016
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1
Building Your Own Turtle Functions
For making really cool pictures!
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5 Cool Things…
1. Variables and Arithmetic
2. Branches for variety
3. Using Functions
4. Building your own Functions (Today)
5. Loops to repeat (Next class)
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Review:1) Variables and Arithmetic
var n = 4;
var y = 2;
var x = n + y;
y = n * 2;
document.write(“x=” + x + “, y=” + y);
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2) Using Functions
Math Functions:x = Math.sqrt(81);y = Math.sqrt(x);document.write(“x=” + x + “, y=” + y);
Turtle Functions:forward(20);left(90);forward(20);right(135);backward(40);
Identify the Function calls and the arguments
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Which command(s) uses “relative” positioning, and which “absolute”
forward -- move turtle forward some number of pixels
left – turn left some number of degrees
moveTo -- move to an x,y coordinate
turnTo – turn to a particular degree heading
home – send turtle back to center of screen, facing up
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Today—3) Building your own functions
Lets you “abstract” a collection of moves
For example, these lines make a square:forward(20); right(90);
forward(20); right(90);
forward(20); right(90);
forward(20); right(90);
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If you want to draw a lot of squares, put this Function Definition at the top of your script…
function square( )
{
forward(40); right(90);
forward(40); right(90);
forward(40); right(90);
forward(40); right(90);
}
This is a Function Definition
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Now you can ‘call’ your square function
square();
--------------------
left(30); square();
left(180); square();
moveTo(-300, -100);
left(30); square();
left(180); square();
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Functions help manage complexity
You can do interesting patterns without a lot of repetition of code
They save time and effort
Functions can use other functions
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What if you want different sizes of squares?
function square( n )
{
forward(n); right(90);
forward(n); right(90);
forward(n); right(90);
forward(n); right(90);
}
n is called a parameter
It’s a variable that receives
the size of the square
(given as the argument in the function call)
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Now when you call the square function, just say how big you want it to be
square(100);
square(50);
square(25);
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You can generate random sized squares…
var size, angle;size=rand(50,100); square(size);angle=rand(0,180); turnTo(angle);size=rand(50,100); square(size);
rand(low, high) gives random number between low and high
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Every time you run the code from last slide, it gives a different result
It’s interesting to observe the variations and similarities
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ProgramStructure
Function Definitions
(in <head>)
Main program block
(in <body>)
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Functions Give “Vertical Structure”How to draw
this complicated mosaic of 120 triangles?
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“Bottom Up” Problem SolvingSolve this sequence of ever more complex problems using functions at each level.
triangle pattern line mosaic
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Solutions
function triangle(n)
{
forward(n); right(120);
forward(n); right(120);
forward(n); right(120);
}
function pattern(n)
{
turnTo(30);
triangle(n); right(90);
triangle(n); right(90);
triangle(n); right(90);
triangle(n); right(90);
turnTo(90);
}
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That’s all!
function line(n){pattern(n);jumpFwd(n*1.7);pattern(n); jumpFwd(n*1.7);pattern(n); jumpFwd(n*1.7);pattern(n); jumpFwd(n*1.7);pattern(n); }
function mosaic(n){jumpTo(-200,-100);line(n);jumpTo(-200+30*1.7, -100);line(n);jumpTo(-200+30*2*1.7, -100);line(n);jumpTo(-200+30*3*1.7, -100);line(n);jumpTo(-200+30*4*1.7, -100);line(n);jumpTo(-200+30*5*1.7, -100);line(n);}
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Not Quite!We need an initial function call to mosaic to kick it off:
mosaic(30);
Notice we give a size of 30…fills in for ‘n’ in all the other functions.
So…using functions we can draw 120 triangles (or 360 forward commands) with about 30 lines of JavaScript—powerful!
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Capture your images in a “screen shot”
Press Alt and PrtScr at same time
Open Paint
Edit/Paste
You can chop out image using select tool Dotted line box
Then paste into Microsoft Word
Or save as a .jpg file (project 2)
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That’s it! Have fun in lab
SUMMARY—Functions let you create your own building blocks to use in more complex programming problems
Functions abstract pieces of code—self documenting
Functions can call other functions
Functions are re-usable—save time and money in software development
Next week…branches and loops
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