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Tangent to Beziers (Tangiers?)

From: David Turner <novalis@fsf.org>
Date: Thu, 05 Aug 2004 12:34:27 -0400
To: www-svg@w3.org
Message-Id: <1091723666.23804.6559.camel@banks>

I'm trying to implement proper direcionality for path
markers in Inkscape (the current version is entirely
nonconforming).  

Here's what 11.6.2 tells me:

"(a) if there is a path segment coming into the vertex and
another path segment going out of the vertex, the marker's
positive x-axis should point toward the angle bisector for
the angle at the given vertex, where that angle has one side
consisting of tangent vector for the path segment going into
the vertex and the other side the tangent vector for the
path segment going out of the vertex ..."

Question: What is the tangent vector to the initial point of
a curve, when the first control point is identical to the
initial control point?  My guess (based on eyeballing the
curves onscreen) would be to devolve to the direction from
the initial point to the second control point, then to the
end point, then to the rules for zero-length path segments
(in the implementation notes).

Is this correct?

I'm not subscribed to the mailing list, so please CC me on
replies.
-- 
-Dave Turner
GPL Compliance Engineer
Support my work: http://svcs.affero.net/rm.php?r=novalis&p=FSF
Received on Thursday, 5 August 2004 12:38:39 UTC

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