CMU CS Regular Poygons and Stars

CMU CS 1.3.3 Regular Polygons and Stars

​Regular Polygons

We know how to draw a square -- we use Rect and make the width and height the same. But what about a triangle? Or a pentagon (with 5 sides) or a hexagon (with 6 sides), and so on? These are called regular polygons, and we draw these using

RegularPolygon.

​We draw a regular polygon similarly to a circle -

- with an (x,y) center and a radius.

We just need one more argument: the number of points (or sides, if you prefer, since there are the same number of points as sides). Here is how we draw a hexagon centered at (200, 100) with a radius of 75:

​RegularPolygon( 200, 100, 75, 6 )

​We can see that this fits just inside a circle:

​Circle(200, 100, 75, fill='cyan') RegularPolygon(200, 100, 75, 6)

Multiple Choice

What happens if you run the previous code with 100 sides?

• It looks like a square.

• It looks like a line.

• It looks like a circle.

• It crashes (you cannot draw a 100-sided regular polygon).

​Circle(200, 100, 75, fill='cyan')

RegularPolygon(200, 100, 75, 100)

​Stars

We draw a star in the same way that we draw a RegularPolygon:

​Star(200, 100, 75, 5)

​We can see that this, too, fits just inside a circle:

​Circle(200, 100, 75, fill='cyan')

Star(200, 100, 75, 5)

​Roundness

You probably have a clear idea what a 5-sided star should look like -- basically, like it does on any flag. Same goes for a 6-sided star. But a 7-sided star is less obvious.

Which of the following is the right shape for a 7-sided star? 7-sided stars of different roundnesses. We see that there are many different kinds of 7-sided stars, some are more circular or rounder than others. The same is true for all stars. When we create a star, we can set its roundness to any value between 0 and 100. For example:

​Star( 80, 130, 35, 7, roundness=20) Star(160, 130, 35, 7, roundness=40) Star(240, 130, 35, 7, roundness=60) Star(320, 130, 35, 7, roundness=80)

Dropdown

Complete the code for the center diamond.

Star (​

Select answer

,​

Select answer

,​

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,​

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, fill='crimson', roundness=​

Select answer

)

Dropdown

Complete the code for the diamond beneath the number 2.

Star (​ ​

Select answer

,​ ​

Select answer

,​ ​

Select answer

,​

Select answer

, fill='crimson', roundness=​

Select answer

)