Re: GTK+3 - A common event handler - possible?

[Donn <donn ingle gmail com>]

On 22/05/2013 09:29, Bernhard Schuster wrote:
> In general factoring code is good (at least that's my opinion) - what
> you are trying to do is the reverse and will give you one very big
> function, hardly readable.
I take your very good point.

> I really suggest you to go with seperate handlers. If you need cross
> handler information, then you should create yourself a context object
> and store desired information into that and obtain it from that, you can
> simply pass the context object as the user_data gpointer.
I will attempt grokkage of this user_data thing. I've seen it in the C 
docs, but I'm newly into Vala, and it looks ... weird:
https://live.gnome.org/Vala/SignalsAndCallbacks (at end)


> Why do you want to disabel doublebuffering in the first case?
Two zones of reasons, both hopefully full of fail and new hope! :P

A:
As it seems now , in order to discover whether the cursor in inside a 
shape, I have to draw a path and use cr_in_fill().
This can only happen when I have a Cairo context! That only happens in 
the draw() signal handler!

 So, in order to simply discover this fact, I have to force a complete 
redraw (queue_draw()) and this then draws *all* my canvas objects again, 
from scratch. A very heavy burden for one mouse motion event.

(Add to this that the object which I am motioning over may be under 
several transforms. i.e. I have to transform several times before I get 
to draw that path in order to test in_fill)

B:
Also, I'm still struggling with the various options - I can draw every 
object from bottom to top, on every draw().
 I can draw each object to a memory surface  (cairo pattern) and then 
compose them all, back to front, every draw().

The thing is - *if* the canvas has *not* changed, *but* I have a tool or 
icon on the topmost layer that moves (I call it a sprite) by a few 
pixels, then it makes more sense to do a small blit of the old 
background and draw the sprite in a new position - rather than drawing 
all my canvas objects again just so I can draw the sprite in a new position.

Thus, the double-buffering that blanks the canvas screws the pooch ;)


> In case that is not really important to you, you could have a look at
> goocanvas..
I guess I'm just keen to see if I can do this (a canvas vector art zui 
draggy thing) on my own. I have the Goo source but it's just as 
confusing to me as the Inkscape source. Still, I do try.

Thanks for your mail, I'd love to hear any further thoughts.
\d