World: r3wp

Can you describe what the iterator does so I may translate the concept 
to rebol ?

Oh, it's been a while, since I did C++, but it's something like:
6 private (internal) variables: den, den_step ... nom_y_step
2 public: x and y
Constructor iterator_x without arguments does nothing.

Constructor iterator_x with 3 arguments (and a constant!? The constant 
is an 8D vector) does (REBOL code):
den: (m[6] * tx) + (m[7] * ty) + 1.0
...
y: nom_y / den

Then an operator ++, so you can write: iterator_x_object++;

And the operator runs the code in the function. End of class definition 
at the };

Then some sort of begin situation!? I think, if you make an object 
of class iterator_x, you give 3 arguments: x, y and step. Then m_mtx 
is added from somewhere. m_mtx must be defined somewhere else, I 
guess.

So in all, an instance of the class iterator_x is made giving 3 arguments, 
and the constant m_mtx is added from somewhere. The iterator is used 
by using the operator ++, and the 2 variables x and y can be seen 
from the outside world.

(The instance is not made here, but can be made. This is just definition 
code.)

My REBOL code is wrong. :-) It should be:
den: (m/6 * tx) + (m/7 * ty) + 1.0

It's a bit weird, that m_mtx is 2 dimensional [8][1]. It's like in 
REBOL:
m_mtx: [[1.0] [2.0]Ê[3.0].... [8.0]]
where you could just do:
m_mtx: [1.0 2.0 3.0 ... 8.0]

If you choose the first way, you have to write:
den: (m/6/1 * tx) + (m/7/1 * ty) + 1.0

I think it helps in operations with other matrices, eg: [8][8]

Probably.

(don't forget to add 1  -->> m[6][0] --> m/7/1

oh yes, you're right. Did it help with your c++ -> REBOL conversoin?

but thanks for your overview. What's confusing to me was the constructor 
variable initialisation after the : (colon). I remember that notation 
now, and I think it looks so stupid, like they're function calls.

I haven't converted this yet, but about to..

Yes, confusing. It's like they want everything to be classes, even 
basic datatypes like double. So you can initialize a double with 
something looking like a function call. Pure object-orientation is 
not good. :-)

:) Here is how I will translate it:
	iterator-x: context [
		den: none
		den-step: none
		nom-x: none
		nom-x-step: none
		nom-y: none
		nom-y-step: none

		x: none
		y: none

		init: func [tx ty step m][
			den: 
		]

		++: func [][
			den: den + den-step
		]
	]

Full translation like this (checking for bugs):
	iterator-x: context [
		den: none
		den-step: none
		nom-x: none
		nom-x-step: none
		nom-y: none
		nom-y-step: none

		x: none
		y: none

		init: func [tx ty step m][
			den: m/7/1 * tx + (m/8/1 * ty) + 1.0
			den-step: m/7/1 * step
			nom-x: m/1/1 + (m/2/1 * tx) + (m/3/1 * ty)
			nom-step: m/2/1 * step
			nom-y: m/4/1 + (m/5/1 * tx) + (m/6/1 * ty)
			nom-y-step: m/5/1 * step
			x: nom-x / den
			y: nom-y / den
		]

		++: func [][
			den: den + den-step
			nom-x: nom-x + nom-x-step
			nom-y: nom-y + nom-y-step
			d: 1.0 / den
			x: nom-x * d
			y: nom-y * d
		]
	]

	iterator-x-begin: func [x y step][
		make iterator-x [init x y step m-mtx]
	]

Now to figure out how to use these functions...

It looks good to me.

Holy crap I think it's working !

First test...
do %agg-simul-eq.r
do %agg-trans-perspective.r

; test
trp: make trans-perspective [

 init reduce [10 10 200 100 [10 10 200 10 200 300 10 300]] ; [x1 y1 
 x2 y1 x2 y2 x1 y2]
	probe transform 50 50
]
==> [50.0 138.888888888889]

Excellent... :) Transforming a grid of points works. >:D

Grats! :-)

in plain English, what's the breakthrough here?

My guess is, that Anton made a function in REBOL like IMAGE used 
in the DRAW dialect. It takes 4 points and do some calculations producing 
a modified image. Like what I do in Canvas, when you use perspective. 
I'm using DRAW for that, Anton is converting the routine from AGG 
C++-source.

Maybe something like this:

view layout [box 400x400 effect [draw [image logo.gif 20x20 380x50 
300x380 40x100]]]

because we can
?

Not quite, although I think I could. What I have done is made a function 
which can transform a point from one space into another. Eg, for 
Geomol's example above, it maps from the image (logo.gif) space into 
the final rendered space shown on screen. So I could ask for any 
point in the image and find out where it is rendered to at the end.

It's good because it matches exactly the algorithm AGG uses to draw 
the image (I am pretty sure anyway .:)

Yep, locked on solid :)

Anton, what is your plan with it? For what use do you need such a 
space-transformation routine?

Ahaha.... :)

Think - reverse transform.

You have a "twisted" image and want the original one!? :-)

not image - individual points, one at a time

Why View should not admit defeat.
http://home.wilddsl.net.au/anton/rebol/virtual-face_xvid.avi

anton, ahhh, so that's what you needed it for :-) very, very good 
demo

that is pretty neat anton!

actually that is almost slashdottable

but I wouldn't do that to anton's server...

where's the source?

somewhere in the Australian wilderness?

I wouldn't call Melbourne a wilderness!

Not that I would ask a user to use a rotated and skewed gui..!

Why not ? Novell with their XGL on the rotated desktop thinks it's 
useful.

Actually Melbourne is a bit of a wilderness, in a way.

source coming... hang on

Not familiar with Novell/XGL.  Got a link?

it's a linux thing

Here, but there is a video somewhere...
http://www.novell.com/linux/xglrelease/

I"m trying to install Suse on a new AMD motherboard and it doesn't 
recognise the video on the motherboard, and so get some rather disturbing 
effects.