Re: TODO item: proportional scaling

On Wed, 1 May 2002, Titus J. Anderson wrote:
I was looking through the TODO file for dia and ran across the following:

* If you hold down shift while moving the handle of an 'Element',
  scale while keeping same proportions.

So, I thought I'd try my hand at it. 

Excellent!  Somebody is actually *reading* that list:)

It only works for boxes right now, but shouldn't be too difficult to make
it work for the other basic objects.  Here's the patch for v0.88.1 (I'm
not working with the CVS version at this point.)

Thank you!  We may hold off on applying it until the shortly upcoming new
release, as we're trying to stabilize Dia.

I don't know that this is the best way to do this, but it does work.  The
basic idea is in addition to the width and height, keep a copy of the
aspect ratio of an element in the element object.  Then, when resizing,
if the shift key is pressed, call the element_move_handle_aspect function
rather than element_move_handle.  The element_move_handle function
updates the aspect ratio when it's finished while
element_move_handle_aspect does not, since it should be the same.  That's
about it.  Just have to make sure that the aspect ratio is calculated
anytime the height or width changes. 

Putting the aspect ratio calculation into foo_update_data is probably the
safest way.

The only real trouble comes when
the height or width is 0.  This is a little tricky and I used some ugly
hacks to make it work.  Oh, I have to keep track of the ratio in the
element (I guess you could keep it in the box, but then it can't be used
in other objects) because if an object ever gets a width or height of
zero, you don't want to recalculate the ratio.  Also, if you calculate
the ratio everytime the move_handle method gets called, if the width goes
to zero, the aspect ratio does as well, and then weird things start
happening (I had what looked like 5 unconnected handles stuck to the side
of the window.)

Here's a slightly alternative approach: Only keep the aspect ratio around
while resizing with ratio fixed.  Initialize the aspect ratio to -1, then
if we move with Shift, calculate the aspect ratio.  When changing the
coordinates, use the aspect ratio if != -1.  When moving stops, reset the
ratio to -1.  That should make sure that the aspect ratio is current
without needing changes all over.


Lars Clausen (| Hårdgrim of Numenor
"I do not agree with a word that you say, but I   |----------------------------
will defend to the death your right to say it."   | Where are we going, and
    --Evelyn Beatrice Hall paraphrasing Voltaire  | what's with the handbasket?

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