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Re[2]: [Gnash-dev] Re: point test

From: Udo Giacomozzi
Subject: Re[2]: [Gnash-dev] Re: point test
Date: Mon, 5 Nov 2007 13:44:38 +0100

Hello Sandro,

Monday, November 5, 2007, 12:05:23 PM, you wrote:
SS> Topologies are made of nodes, edges and faces.
SS> Two intersecting edges would be invalid (missing node info).
SS> Normalizing would mean finding all intersections and defining all faces
SS> by the edges that bound them.
SS> I'm not sure we need such a representation.

Hmm, Bastiaan's description is a bit different. Anyway, a Flash shape
should never have any intersecting edges, i.e. Flash itself normalizes
the shape.

SS> Scaling the query point would only mean reducing its precision to
SS> match the precision of the source coordinates (twips).
SS> Now the question would be: is it worth it to use higher precision ?
SS> At which cost ? I can't think of a real-world case in which this would
SS> be relevant.

Sure it is. I didn't look at the AGG (the core lib) implementation in
detail, but I'm pretty sure it works just like the rendering process

Say, you have a shape that's only 2 TWIPs wide. If you put the shape
at 1:1 scale on the stage it will be barely or not at all visible
(since it is only 0.1 pixels wide). A point test at that pixel might
fail (since the *renderer* might say 10% coverage is not enough). So
far so good.

Now, if you scale the same shape by factor 100x it becomes 200 TWIPs =
10 pixels wide. You have no problem clicking inside this shape with
the mouse but the renderer would still do the point test with the
normal-sized shape and thus won't give a positive result.

It's theoretical math versus practical implementation...

Solution: provide transformation matrix and check the transformed


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