Set up a framebuffer object (refer to the Rendering to a texture recipe in Chapter 5, Using Textures) that has the same dimensions as the main window. Connect the first color attachment of the FBO to a texture object in texture unit zero. During the first pass, we'll render directly to this texture. Make sure that the mag and min filters for this texture are set to GL_NEAREST. We don't want any interpolation for this algorithm.

Provide vertex information in vertex attribute zero, normals in vertex attribute one, and texture coordinates in vertex attribute two.

The following uniform variables need to be set from the OpenGL application:

• Width: This is used to set the width of the screen window in pixels
• Height: This is used to set the height of the screen window in pixels
• EdgeThreshold: This is the minimum value of g squared required to be considered on an edge
• RenderTex: This is the texture associated with the FBO

Any other uniforms associated with the shading model should also be set from the OpenGL application.