Drawing to an offscreen canvas

In this recipe, we will learn how to draw in an offscreen canvas using the OpenGL Frame Buffer Object (FBO).

We will draw in an FBO and draw it onscreen as well as texture a rotating cube.

Getting ready

Include the necessary files to work with OpenGL and the FBOs as well as the useful include directives.

Add the following code to the top of the source file:

#include "cinder/gl/gl.h"
#include "cinder/gl/Fbo.h"

using namespace ci;

How to do it…

We will use a ci::gl::Fbo object, a wrapper to an OpenGL FBO, to draw in an offscreen destination.

1. Declare a ci::gl::Fbo object as well as a ci::Vec3f object to define the cube's rotation:

   gl::FbomFbo;
   Vec3f mCubeRotation;

2. Initialize mFbo with a size of 256 x 256 pixels by adding the following code in the setup method:

   mFbo = gl::Fbo( 256, 256 );

3. Animate mCubeRotation in the update method:

   mCubeRotation.x += 1.0f;
   mCubeRotation.y += 1.0f;

4. Declare a method where we will draw to the FBO:

   void drawToFbo();

5. In the implementation of drawToFbo...