An ofSketch showing that the order in which transparent objects are drawn in openGL matters

TransparencyOrder.sketch

ofEasyCam cam;

void setup() {
    ofSetWindowShape(800, 400);    
	ofSetRectMode(OF_RECTMODE_CENTER);
}

void draw() {	
    ofEnableBlendMode(OF_BLENDMODE_DISABLED);
	ofBackground(ofColor::white);
	
    ofEnableBlendMode(OF_BLENDMODE_ALPHA);	
	cam.begin();
	    // Center the camera over the rects
	    ofTranslate(-150, 0, 0);
		
		// Draw red on blue
    	ofSetColor(255, 0, 0, 127);
    	ofRect(0, 0, 100, 200, 200);		
    	ofSetColor(0, 0, 255, 127);
    	ofRect(0, 0, 0, 200, 200);
    	
		// Draw blue on red
    	ofSetColor(0, 0, 255, 127);
    	ofRect(300, 0, 100, 200, 200);	
    	ofSetColor(255, 0, 0, 127);
    	ofRect(300, 0, 0, 200, 200);	
    cam.end();
}