Re: avoiding drawing tiny objects in foocanvas

[Rob Clack <rnc sanger ac uk>]

Jody Goldberg wrote:
> On Wed, May 12, 2004 at 04:26:00PM +0100, Rob Clack wrote:
>
> > I'm drawing tens of thousands of rectangles, using foocanvas to 
> > (successfully - thanks Jody!) speed things up, but when zooming out I 
> > would like there to come a time when rectangles too small to be 
> > correctly rendered are not drawn at all.
> >
> > At present there seems to be a minimum size beyond which they don't 
> > shrink, so eventually they all merge into each other.  It's as though 
> > the code says "OK, this is as small as this one gets" and keeps drawing 
> > it that size, whatever the zoom factor.  I want it to say "This one's 
> > too small to bother with, so I won't draw it at all"
> >
> > I accept I'm going to have to hack the foocanvas source code, but so far 
> > can't find where it is that this decision is being made.
> >
> > Anyone know where I should be looking?
>
>
> libfoocanvas/foo-canvas-rect-ellipse.c : foo_canvas_rect_draw 
>
> Throw in some tests to see whether it is useful to draw something
> small, or even if it is useful to draw the inside of something
> overlapped by it's outline
My apologies for asking the wrong question and this post includes both 
the right question and what I think is the right answer, just to tie up 
the loose thread.

What I wanted to know was how to hide objects that were too small to be 
worth drawing, but still have them appear when you zoomed in far enough.

In foo-canvas-rect-ellipse.c I put a test into foo_canvas_rect_update() 
to determine whether or not I wanted the rectangle visible, then used
foo_canvas_item_hide() and foo_canvas_item_show() as appropriate.

Thank you Jody for yet more help!
Rob
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 Rob Clack                        Acedb Development,  Informatics Group
 email: rnc sanger ac uk                Wellcome Trust Sanger Institute
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