On 12/7/2010 9:53 AM, John Nagle wrote: > On 12/5/2010 2:49 PM, Martin Manns wrote: >> Hello, >> >> I am looking for a Python library for 2D collision checks of rotated >> rectangles. Currently, I have found vizier 0.5b that is based on pygame. >> >> Since I do not want to add a pygame dependency to my app, I replaced the >> pygame.rect.Rect by a wxPython wx.Rect (see code below). >> >> However, collision checks do not work correctly, i. e. identical rects >> are not found to be colliding: > > Probably because you seem to be trying to compute the intersection > point for coincident lines, which is not well-defined. > > I don't have time to debug this, but you might want to get some > basic books on game programming and graphics. > > Incidentally, a dictionary lookup in Python is far more expensive > than computing trig functions. If you need to speed this up > for large numbers of rectangles, there are algorithms that are > several orders of magnitude faster. Realistically, though, > this is the kind of problem that runs slow in CPython. > That appears to be (from a rather limited investigation) a wild-assed assertion unjustified by anything other than preconceptions.
With d as a dict containing 100 random numbers from (0,1) I see this: >>> def fm(): ... x = random.random() ... return math.sin(x) ... >>> def fd(): ... x = random.random() ... return x in d ... >>> timeit.timeit(fm) 0.58099985122680664 >>> timeit.timeit(fd) 0.55200004577636719 >>> Of course it's possible that the random number generation is dominating, but I'd still like to see some proof. I know for a fact that dict lookup has been extensively optimized, and while I am no longer involved in numerical computing it seems to me there's still a lot to do to compute a sin unless your CPU will do it for you. regards Steve > This is why you don't write your own collision library. > (I once did, for 3D, but that was in 1996, when it was > cutting-edge technology.) > > John Nagle -- Steve Holden +1 571 484 6266 +1 800 494 3119 PyCon 2011 Atlanta March 9-17 http://us.pycon.org/ See Python Video! http://python.mirocommunity.org/ Holden Web LLC http://www.holdenweb.com/ -- http://mail.python.org/mailman/listinfo/python-list
