coordinate system of computer screen figure - the cartesian coordinate system on computer screen it is common that computer screens use coordinate system that has the origin ( at the top left corner of the screenwhich increases going down and to the right this is shown in figure there are no negative coordinates most computer graphics use this coordinate systemand you will use it in this book' games summary most programming doesn' require understanding lot of math up until this we've been getting by on simple addition and multiplication cartesian coordinate systems are needed to describe where in two-dimensional area certain position is coordinates have two numbersthe -coordinate and the -coordinate the -axis runs left and right and the -axis runs up and down on computer screenorigin is in the topleft corner and the coordinates increase going right and down the three tricks you learned in this make it easy to add positive and negative integers the first trick is that minus sign will eat the plus sign on its left the second trick is that two minuses next to each other will combine into plus sign the third trick is that you can swap the position of the numbers you are adding for the rest of the bookwe will use the concepts from this in our games because they have two-dimensional areas in them all graphical games require understanding how cartesian coordinates work post questions to