Drawing basics

The screens of modern computers consist of a number of small squares, called pixels (picture elements). Each pixel can light in one color. You create pictures on the screen by changing the colors of the pixels.

The openFrameworks project can draw on the whole screen (when it is in fullscreen mode) or only in a window (when fullscreen mode is disabled). See how to set screen modes in the main.cpp and setup() sections in Chapter 1, openFrameworks Basics. For simplicity, we will call the area where openFrameworks can draw, the screen. The current width and height of the screen in pixels may be obtained using the ofGetWidth() and ofGetHeight() functions.

For pointing the pixels, openFrameworks uses the screen's coordinate system. This coordinate system has its origin on the top-left corner of the screen. The measurement unit is a pixel. So, each pixel on the screen with width w and height h pixels can be pointed by its coordinates (x, y), where x and y are integer values lying in the range 0 to w-1 and from 0 to h-1 respectively.

In this chapter, we will deal with two-dimensional (2D) graphics, which is a number of methods and algorithms for drawing objects on the screen by specifying the two coordinates (x, y) in pixels.