Flowers and Other Curves

We have seen that is is useful for methods to accept functions as parameters. In this section we'll see that it is useful for methods to return functions. In doing so we'll create the flower-like pictures that were our goal going into this chapter.

We've seen all the basic steps we need to make our flowers. Now we just need to know the curve that makes the flower shape! The shape I used is known as the rose curve. One example is shown below.

Here's the code for the parametric curve.

// Parametric curve for rose with k = 7
val rose7 = (angle: Angle) =>
  Point((angle * 7).cos * 200, angle)

You may wonder why I called this function rose7. It's because we can vary the shape by changing the value 7 to something else. We could make a method or function to which we pass the value of this parameter and this function would return a particular rose curve. Here's that idea in code.

def rose(k: Int): Angle => Point =
  (angle: Angle) => Point((angle * k).cos * 200, angle)

The rose method describes a family of curves. They all look similar, and we create individual curves by choosing a particular value for the parameter k. Below we show more rose curves, this time with k as 5, 8, and 9 respectively.

Let's look at some other interesting curves. Below we show examples of a family of curves called Lissajous curves.

The code for this is

def lissajous(a: Int, b: Int, offset: Angle): Angle => Point =
  (angle: Angle) =>
    Point(100 * ((angle * a) + offset).sin, 100 * (angle * b).sin)

The examples use values of a and b of 1, 2, or 3, and the offset set to 90 degrees.