J2ME in a Nutshell

Translating the Graphics Origin

The origin of the Graphics object that you get in the paint( ) method is initially placed at the top left of the Canvas. However, you can move it to any location you choose using the translate( ) method:

public void translate(int x, int y)

This method relocates the origin to the point (x, y) as measured in the coordinates that apply before this call is made. If the paint( ) method begins with the following statements:

g.drawLine(0, 0, 20, 0);
g.translate(10, 10);
g.drawLine(0, 0, 20, 0);

a line is first drawn along the top of the Canvas from (0, 0) to (20, 0), the origin is shifted so that (0, 0) is at the point (10, 10) relative to the top left corner of the Canvas, and finally another line is drawn. This line stretches from (0, 0) to (20, 0) in the new coordinate system, which is the same as (10, 10) to (30, 10) relative to the the Canvas itself. Figure 5-12 illustrates the effect of moving the origin.

Figure 5-12. Translating the Graphics origin

Once you have moved the origin, the effect of another translate( ) call is cumulative with respect to the first. This means that, for example, the following code results in the origin being moved to (10, 10) and then back to its initial location:

g.translate(10, 10);
g.translater(-10, -10);

The following code moves to the origin to (15, 15) relative to the top left-hand corner of the Canvas:

g.translate(10, ...