simple texture feedback example (untested)

gistfile1.cpp

//in your .h file if using one
ofShader shader;
ofFbo fbo;
int w, h;

//in .cpp file
void ofApp::setup(){
	w = 640; h=480;
 	ofEnableDataPath();
	ofSetWindowShape(w,h);
	ofEnableArbTex();
	shader.load(ofToDataPath("<name of your shader>"));
	fbo.allocate(w,h,GL_RGBA);
}

void ofApp::draw(){
    fbo.begin();
    shader.begin();
    shader.setUniformTexture("state", fbo.getTextureReference(), 0);
    //execute the shader for each pixel in fbo
    ofRect(0,0,fbo.getWidth(),fbo.getHeight());
    shader.end();
    fbo.end();

    //draw to the screen
    fbo.draw(0,0);
}