Re: [pygame] Rotate image around another point?

[John Eriksson <john@xxxxxxxxxxxx>]

Wher reading Ulfs answer a little more carefully I thinks that it's just
what he is sugesting. *smile*

/John

tor 2007-04-19 klockan 12:31 +0200 skrev John Eriksson:
> But maybe it'll work if you first rotate the imagedata around the
> centerpoint using pygame.transform.rotate(...) and then rotate the
> centerpoint around the wanted rotation point? Havn't tried it yet
> though. Sounds reasonably but what do you think?
> 
> /John
> 
> tor 2007-04-19 klockan 12:24 +0200 skrev altern:
> > john is talking about the actual image surface data not just the sprite 
> > location. i guess you might need something like PIL library, but i would 
> > not really know how to do this.
> > 
> > John Eriksson(e)k dio:
> > > But that is not what I'm trying to do.I want to rotate the actual
> > > imagedata (like rotating an image using PohotSshop or GIMP). Not just
> > > the location where the image is drawn. 
> > > 
> > > The pygame.transform.rotate(...) function does that but always rotates
> > > the imagedata about it's center.
> > > 
> > > /John
> > > 
> > > tor 2007-04-19 klockan 11:02 +0200 skrev Ulf EkstrÃm:
> > >> On 4/19/07, John Eriksson <john@xxxxxxxxxxxx> wrote:
> > >>> Well, no.
> > >>>
> > >>> I'm looking for a way to rotate the imagedata (like
> > >>> pygame.transform.rotate(...)) but your example rotates the image
> > >>> location. Right?
> > >> It is actually the same thing. Rotation around some arbitrary point
> > >> can be decomposed into a rotation around some other point followed by
> > >> a translation. Suppose you have a function R which rotates things
> > >> around the origin. To write a function Rp which rotates around the
> > >> point p (p and q are vectors), you do
> > >>
> > >> Rp(q) = R(q-p)+p
> > >>
> > >> Since R is a linear function you can do
> > >>
> > >> Rp(q) = R(q) + p - R(p)
> > >>
> > >> So rotating around p is the same as rotating around the origin and
> > >> then translating by p - R(p).
> > >>
> > >> Ulf
> > > 
> > >