When you draw you need a space to draw on to. We call this space
a Canvas. A Canvas is made up of tiny colored blocks called pixels.
Typically a pixel is about 1/72th of an inch square. You can
specify how many pixels wide and high your Canvas is.
If you are drawing onto the Canvas you need to specify where you
want your drawing to take place. You do this by giving the distance
from the top left of the Canvas. You need a horizontal offset and a
vertical offset (often called the x and y
coordinates respectively). These offsets are measured in
numbers of pixels starting at zero. Together these two coordinates
are called a Point.
The point at the top left of a Canvas is always 0,0 and is often
called the Origin.
Often you need to use groups of points to specify what you want
drawn and where. Say you want to draw a line. To describe where you
it to be you need to state a start Point and an end Point. Many
shapes are described using sets of Points. For instance, a
rectangle only needs two Points to describe it (just like the