Re: drop shadow

[Hans Breuer <hans breuer org>]

Am 26.07.2008 09:37, Lars Clausen schrieb:
> On Jul 26, 2008, at 1:27 AM, Abhijit Menon-Sen wrote:
[...]
> > I need drop shadows too, and although I'm not really familiar with Dia
> > or GTK, I would like to at least try to implement them, if anyone has
> > advice about how best to proceed.
>
> Take a look at how highlighting is done, you may be able to adapt the 
> method to drop shadows, i.e. have a round of drawing drop shadows for 
> those objects that have them before the round of drawing the objects 
> themselves. 
I have added something conceptionally similiar to dia-renderer.dia. But IMO 
future enhancements in this direction should be encapsualted in dedicated 
renderers. One could think of a renderer chain of resposibilities [1] where 
the DropShadowRenderer modifies the calls from normal rendering to add the 
shadow and translates/modifies them to what the contained 'standard' 
renderer understand.

There is no code allowing this yet.

> However, some exporters may have a different idea of how 
> drop shadows are best represented. Since highlighting isn't exported, 
> the highlight algorithm doesn't have that problem.
I think the that most of the highlightning could have been implemted by 
simple delegation, but for the special text editing highlighting it 
wouldn't have worked with existing interfaces.

> > Could it be done with a Python plugin, perhaps?
>
> I'll leave that for Hans to answer.
It is possible to implement complete renderers in Python, see diasvg.py [3] 
for a complex example. It should be possible to implment a complete cairo 
renderer including drop shadow with pydia and pycairo [4]. First step would 
be to 'translate' the existing cairo renderer [5] to Python (basically just 
diacairo-renderer.c)

It is not yet possible to reuse existing DiaRenderers from pydia, but the 
above mentioned renderer chain is not implemented in C either.

        Hans

[1] http://en.wikipedia.org/wiki/Chain-of-responsibility_pattern
[2] http://en.wikipedia.org/wiki/Decorator_pattern
[3] http://svn.gnome.org/viewvc/dia/trunk/plug-ins/python/diasvg.py?view=markup
[4] http://www.cairographics.org/pycairo/
[5] http://svn.gnome.org/viewvc/dia/trunk/plug-ins/cairo/

-------- Hans "at" Breuer "dot" Org -----------
Tell me what you need, and I'll tell you how to
get along without it.                -- Dilbert