​The Canvas

To understand what is going on, we first have to talk about the canvas. In this course, all drawing is done on a canvas.

The canvas is made up of tiny colored points, or pixels. We use (x,y) coordinates to talk about pixels on the canvas, like so:

• (0, 0) is the left-top corner of the canvas (not the middle!).

• As x increases, you head right.

• As y increases, you head down, not up!

• Our canvas is a 400 x 400 square, so (200, 200) is the middle of the canvas, and (400, 400) is the right-bottom corner.

• ​As x increases, you head right.

• As y increases, you head down, not up!

• Our canvas is a 400 x 400 square, so (200, 200) is the middle of the canvas, and (400, 400) is the right-bottom corner.

​(200, 200)

​(400, 400)

​Python is very picky. Here are some rules to follow:

1. Case matters, so Rect is not the same as rect.

2. A command must have the right number of values after it.

   For Rect, that's left, top, width, and height. These values are called arguments. Here are some rules about arguments:

   • They must be in the right order.

   • They must be inside parentheses.

   • They must be separated by commas.

If any of these rules are not followed, you have an error, and your code will not run correctly until you fix the error.