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@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@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.pdfhttp://www.cs.cmu.edu/%7Eph/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@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....
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