I can't understand Double Buffer the example of Actors

[LoranceChen]

Graphic example is great! But I can't comprehend why this code would be "see a slap in the frame after it was actually slapped". void Stage::update() { for (int i = 0; i < NUM_ACTORS; i++) { actors_[i]->update(); }

for (int i = 0; i < NUM_ACTORS; i++) { actors_[i]->swap(); } } example: I have three actors a,b and c,and then,I put them into stage's array,just like: array.add(c,0); array.add(a,1); array.add(b,2); The update function also update slap action in seq frame rather then once. It's also depend on their order in the stage’s array.What's the matter?