If you have two points, you can calculate the angle and from the angle and two points you can draw the line. Now you just have to implement this math things in java and write a algorithm which draw a line from the angle. Am i right?

You're right that you can calulcate the angle from the two points. But how would you draw the line from the angle and two points? There are ways to do it, but they tend to either be potentially imprecise (will miss pixels in some circumstances) or slow. If you think you know a way, try implementing it to see if it works.

Your lines seem to be unusually thick o.O Especially when the angle of the line is 45 degrees. There is an incredibly fast (integer arithmatic only!) line drawing algorithm called the Bresenham's line algorithm that might work better in this situation.

Thanks, Builderboy, the Bresenham's line algorithm looks good. Though I do not understand why we need to know how to draw a line in java, since java.awt.graphics makes this easy.

The answer to Builderboy2005 and MatheMagician is the same: I used Wu (which gives thick lines) rather than Bresenham because the same algorithm can be used to do things like shooting: http://sinepost.wordpress.com/2012/05/29/robotic-outlaws/ and visibility calculation: http://sinepost.wordpress.com/2012/06/08/lines-of-sight/ the latter of which is used again in the raycasting 3D example: http://sinepost.wordpress.com/2012/06/16/raycasting/ Bresenham is not very suitable for these other purposes because it would let the shot/visibility pass through walls -- not so good!

Very good point! I wonder if it would be cool to have a button you could press to switch between the two algorithms, that was you could see how they differ :D

@Builderboy2005 You're right: Bresenham has super fast algorithms (including one for a circle!). I've put them in my Fast graphics scenario, do you want to give some feedback?