10.1 Calculator’s numbers

This theme is based on the fact that every calculator’s number could be drawn with the above schema:

• For example, to draw digit 4, we light rectangles 3,4,5,7.
• To draw digit 8, we light rectangles 1,2,3,4,5,6,7.
• To draw digit 3, we light rectangles 2,3,4,5,6.

10.1.1 Filling a rectangular

If we want to draw a filled rectangle with dimensions 100 by 200, a first idea could be to draw a rectangle 100 by 200 then to draw a rectangle 99 by 199, then a rectangle 98 by 198 ... until the rectangle is fully filled.
Let’s begin by defining a rectangle with two variables corresponding to width and height

To fill our rectangle, we have to run:
rec 100 200 rec 99 199 rec 98 198 ..... rec 1 101

Let’s define a procedure for this filled rectangle.

We test rectangular 100 200 and we can see there is a problem: The procedure doesn’t stop when the rectangle has been filled, it continues infinitely! We must add a breakout test that will detect if width or height is equal to 0. When this condition is realized, we’ll ask the program to stop with the primitive stop.

Note: Instead of using the primitive or, it’s possible to use the symbol |, the line becomes:

10.1.2 The program

We must reuse the precedent filled rectangle:

We suppose that the turtle starts from the bottom left corner. We’re going to define a procedure called number depending on 7 arguments :a, :b, :c, :d, :e, :f, :g. When :a is equal to 1, we draw the rectangle 1. If :a is equal to 0, we don’t draw this rectangle. Here is the main idea.

The code:

10.1.3 Creating an animation

In this part, we’ll define a countdown from 9 to 0.

Little problem: There is a flickering effect during each number drawing. To make the animation fluid, we’re going to use the three primitives animation, stopanimation and repaint.

• animation enables the mode “animation”. The turtle stops drawing on the screen but remembers all changes in cache. To display the image, it’s necessary to use the primtive repaint.
• stopanimation returns to the classic drawing mode.

Here is the new code for this procedure: