Re: gnome-canvas, large items, and MOTION_NOTIFY handling question

[Lauris Kaplinski <lauris ximian com>]

Hello!

You have correctly tracked down the problem.
If you do not need events, then you should just modify canvas item, to return
some very large distance for ::point() method. You didn't specify, whether you
use stock items, or created customs ones - you cannot do that with stock items
unfortunately. But you can just very simple subclass, that overrides ::point
method.
Also, if you need events, you can probably still speed your code up by
modifying ::point(). In current canvas ::point() is supposed to return distance
from point to object - there is little need for exact distance - for most cases
it is sufficent to determine, whether point lies on item, or outside it. Just
check, whether point is inside (using art_svp_wind or something) and return either
0 or 1000000... depending on result.
Hope that helps.

Best wishes,
Lauris Kaplinski


On 22 Feb 2001 14:10:16 -0500, Jan Hlavacek wrote:
> 
> Hi everybody,
> 
> I hope this is the right place to ask.  I am writing a little
> application that uses AA gnome canvas with rulers to track mouse
> position.  It works fine as long as I don't use too complicated items.
> However, in my application I need to use lines with several hundreds
> control points.  Every time mouse cursor enters the bounding rectangle
> of such item, the rulers start seriously laging behind the actual mouse
> cursor.  If I move the cursor several times accross the bounding
> rectangle, I can see the marks on the rulers slowly move around several
> seconds after the mouse cursor stoped. 
> 
> >From what I could figure out, I believe that this is caused by the fact
> that gnome canvas is trying to figure out whether a mouse cursor is over
> the line or not,  which is slow for complicated lines.  What I would
> like to know is this:  Is there any way to stop canvas from trying to
> send mouse events to its items?  Or is there some other way how to speed
> the canvas mouse tracking?  
> 
> BTW, i was able to recreate the same problem in sodipodi.  When you
> create very compicated free-hand line a move mouse cursor over it, the
> marks on the rulers slow down considerably. 
> 
> Thanks for any advice.
> 
> -- 
> Jan Hlavacek                                            (219) 434-7566
> Department of Mathematics                             Jhlavacek sf edu
> University of Saint Francis               http://www.sf.edu/jhlavacek/
> 
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