11 ms·

How hard would it be to solve this deterministically? Can someone comment on the game's physics? I am assuming: - constant horizontal velocity - gravity

by potash 13y ago

How hard would it be to solve this deterministically? Can someone comment on the game's physics? I am assuming: - constant horizontal velocity - gravity - flapping implemented via impulse - collisions are handled with bounding boxes Maybe someone who knows something about optimal control (ODE) say whether this is analytically solvable? Of course there's still the practical stuff (numerical integration, I/O lag) to deal with but I'm optimistic.

kenferry 13y ago
If you play the game, it's actually quite trivial to program deterministically. :-) Flapping is not implemented as an impulse. It's more like jumping in Mario - it instantaneously fires a canned "flap" movement that is always the same. Set flap_height = bottom of next pipe + constant. If bird height < flap_height, flap. Done!
- userbinator 13y ago
  It also looks like you'd want to avoid flapping into the top of the pipe.
  - kenferry 13y ago
    Perhaps I should have said "threshold_height". threshold_height = bottom_of_pipe_height + 10 pixels; // or something if (current_height < threshold_height) flap else don't flap If you never flap when above the threshold, you will not hit the top.
tripzilch 13y ago
In another Flappy Bird thread (the MMO one), somebody posted this formula: Let distance between ground and top of screen=100. Bird position after a flap at y=y0, time=t0: y(t) = y0 + 13.8 - 147 * (t - t0 - 0.288)^2 (https://news.ycombinator.com/item?id=7229018 https://news.ycombinator.com/item?id=7229018 -- note the original comment had "+ 0.288", but if you plot the graph this was obviously a mistake) I tried it out in my own HTML5/JS Flappy clone (mine's not at all interesting or even done, but I felt I had to give it a try), and the movement seems really accurate. I have no idea how they got to those numbers, however.

by potash 13y ago

kenferry 13y ago

If you play the game, it's actually quite trivial to program deterministically. :-) Flapping is not implemented as an impulse. It's more like jumping in Mario - it instantaneously fires a canned "flap" movement that is always the same. Set flap_height = bottom of next pipe + constant. If bird height < flap_height, flap. Done!

userbinator 13y ago
It also looks like you'd want to avoid flapping into the top of the pipe.
- kenferry 13y ago
  Perhaps I should have said "threshold_height". threshold_height = bottom_of_pipe_height + 10 pixels; // or something if (current_height < threshold_height) flap else don't flap If you never flap when above the threshold, you will not hit the top.

tripzilch 13y ago

In another Flappy Bird thread (the MMO one), somebody posted this formula: Let distance between ground and top of screen=100. Bird position after a flap at y=y0, time=t0: y(t) = y0 + 13.8 - 147 * (t - t0 - 0.288)^2 (https://news.ycombinator.com/item?id=7229018 https://news.ycombinator.com/item?id=7229018 -- note the original comment had "+ 0.288", but if you plot the graph this was obviously a mistake) I tried it out in my own HTML5/JS Flappy clone (mine's not at all interesting or even done, but I felt I had to give it a try), and the movement seems really accurate. I have no idea how they got to those numbers, however.