[Newbies] Skewing Forms in Squeak V2

[Iulian Wande Radu]

You're right about the timing.
I'm fairly new to Smalltalk and had already hooked in a DLL for other
things, so found it much easier to work matrix math in C :)

On Mon, Sep 22, 2008 at 7:58 PM, Matthias Berth <
matthias.berth at googlemail.com> wrote:

> Hi Iulian,
>
> I'm glad to hear that it worked for you. I wonder why you implemented
> it in a C DLL... As far as I can see, the manipulations with the
> parameters would be done only once for every quad you want to
> transform. The computation time for that should be negligible compared
> to the time it takes to actually transform all the pixels in the quad
> / rectangle. At least that's what I was thinking, maybe i am wrong?
>
> Cheers
>
> Matthias
>
> On Tue, Sep 23, 2008 at 1:08 AM, Iulian Wande Radu
> <infinite.flow at gmail.com> wrote:
>  > Thank you for the guidelines for skewing forms.
> >
> > I've followed Matthias' instructions (and the associated math doc) and
> > skewing works well this way through WarpBlt. (The code linked by Yoshiki
> was
> > too slow and didn't work fully).
> >
> > I wrote the math conversions in a C DLL, and it would probably be useful
> for
> > people. Is there any place where I could put the code so the community
> can
> > use it ?
> >
> > Cheers,
> > Iulian
> >
> > ---------- Forwarded message ----------
> > From: Matthias Berth <matthias.berth at googlemail.com>
> > Date: Tue, Jul 22, 2008 at 7:10 PM
> > Subject: Re: [Newbies] Skewing Forms in Squeak V2
> > To: "A friendly place to get answers to even the most basic questions
> about
> > Squeak." <beginners at lists.squeakfoundation.org>
> >
> >
> > So it comes down to this:
> >
> > given a projective transformation T from a rectangle (your form) to a
> > quad Q (what you want to draw on screen), how can you express the same
> > transformation in terms of mapping a quad to a rectangle (what WarpBlt
> > needs)?
> >
> > One possible plan is:
> >
> > 1) determine the transformation's parameters
> >
> > 2) take the bounding box of Q (a rectangle R) and transform it by the
> > inverse of T, giving you a quad Q'
> >
> > 3) use WarpBlt to transform pixels in Q' (should be a superset of your
> > form) to R
> >
> > 4) mask the result with your original quad Q, using pixel-by-pixel
> > operations on Forms
> >
> > I think all you need in terms of mathematics for this is in
> > http://www.cs.cmu.edu/~ph/869/www/notes/proj/proj.pdf
> >
> > Hope this helps, feel free to ask about the details,
> >
> > Matthias
> >
> >
> >
> >
> > On Thu, Jul 24, 2008 at 1:39 AM, Yoshiki Ohshima <yoshiki at vpri.org>
> wrote:
> >>
> >> At Tue, 22 Jul 2008 13:53:21 -0400,
> >> Iulian Wande Radu wrote:
> >> >
> >> > Hi, I'd like to skew the graphics of a Form, is there an easy way to
> do
> >> > this in v2 ?
> >> >
> >> > What I want is to take the rectangle from a normal form, transform it
> >> > into an arbitrarily-defined quadrilateral, and
> >> > then paint on the screen. I saw that WarpBlt does something like
> this..
> >> > but it maps a quadrilateral section of a form
> >> > onto a rectangle.
> >>
> >>  There was similar a discussion on this a while ago:
> >>
> >>
> >>
> http://lists.squeakfoundation.org/pipermail/squeak-dev/2001-February/013402.html
> >>
> >> -- Yoshiki
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