> xRel, yRel = self.relPoint # The rotation should be relative to this Shouldn't it be
x -= xRel y -= yRel xR = x * cos(phi) - y * sin(phi) yR = x * sin(phi) + y * cos(phi) then? Regards Franz GEIGER "Karl Max" <[EMAIL PROTECTED]> schrieb im Newsbeitrag news:[EMAIL PROTECTED] > Hi all, > > I'm new here. Name's Max from tuscany, and I don't speak english very well > :-) I am not veteran at coding, I am most like an "artisan coder" since > commodore 64 times. > > Now the problem: > I would like to have a little 2d engine to calculate and trace segments and > poly's and their collisions, rotations and trasformations. I didn't > understand too much in tutorials (you're all high school coders, well > informed in maths and programming theory!!! :-))) so I took my old school > books on Cartesian space and had a refresh. Proceeding in this not too > optimized way of coding my needs, I took down some generic classes to > describe primitive objects in space (vertexes, segments, poly's etc...). > > Now I try to make a point rotate around another point. > Here's my piece of code: > > def rotate(self, w): > # This method belongs to the class Vertex > # w = angle expressed in radiants > x, y = self.coords > xRel, yRel = self.relPoint # The rotation should be relative to this > sin, cos = math.sin(w), math.cos(w) > x = x * cos - y * sin - xRel * cos + yRel * sin + xRel > y = x * sin + y * cos - xRel * sin - yRel * cos + yRel > self.coords = (x,y) > > I know the style isn't professional, and if you should have some piece of > advice, you're welcome... but that's not the question. > When I render it graphically, using pygame 1.6, the point tends to fall > towards the center of rotation round after round. I mean if I have a loop > rotating the point by a fixed angle, the point is like "attracted" by the > center every round it does, like in a vortex. > I think it depends from float representation inside python, but I have no > clear idea about how to resolve it. Maybe should I use Decimal module? Or is > there any trick on this subject (2D vector graphics?) that I can't even > imagine? > Thanks you all, > Max > > -- http://mail.python.org/mailman/listinfo/python-list
