Using FBO for offscreen drawings

FBO in computer graphics stands for frame buffer object. This is an offscreen raster buffer where openFrameworks can draw just like on the screen. You can draw something in this buffer, and then draw the buffer contents on the screen. The picture in the buffer is not cleared with each testApp::draw() calling, so you can use FBO for accumulated drawings.

In openFrameworks, FBO is represented by the class ofFBO.

The typical scheme of its usage is the following:

1. Declare an ofFbo object, fbo, in the testApp class declaration.

   ofFbo fbo;

2. Initialize fbo with some size in the testApp::setup() function.

   int w = ofGetWidth();
   int h = ofGetHeight();
   fbo.allocate( w, h );

3. Draw something in fbo. You can do it not only in testApp::draw() but also in testApp::setup() and testApp::update(). To begin drawing, call fbo.begin() . After this, all drawing commands, such as ofBackground() and ofLine(), will draw to fbo. To finish drawing, call fbo.end(). For example, to fill fbo with...