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Re: [svg2] radialGradient @fr constraints

From: Dr. Olaf Hoffmann <Dr.O.Hoffmann@gmx.de>
Date: Wed, 29 Aug 2012 14:20:28 +0200
To: www-svg@w3.org
Message-Id: <201208291420.28505.Dr.O.Hoffmann@gmx.de>
Looks like the canvas approach is incompatible with the SVG approach.
To avoid backwards incompatibilities one could use 'fr' to trigger the
behaviour for the problematic cases:

If 'fr' is not set or 0, use the old SVG approach to automatically correct
'fx' and 'fy' to be not outside the circle (this has the advantage for 
authors, that they do not have to calculate this manually - and the result
is stable, does not depend on differences of the calculation of the author 
and the viewer, because the author is not required to calculate).

If 'fr' is not set to 0, do not correct 'fx' and 'fy', following the new
'canvas' approach.

Advantage - does not break current content (I have for example such
files - and it was annoying to see in the past, that some viewers did not
manage to do the correction, resulting in a nonsense display).
Minor disadvantage - the 'canvas' approach cannot be used with exactly
fr="0", but because this is usually not noticable different from something 
like fr="1e-20" this should be no restriction for authors wanting to get such
an effect.

What could be the intended effect for a negative 'fr'? 
Define, that the absolute value has to be used, if there is no intended 
effect known.
This is better as to disallow, because if the viewer fixes this, the authors
cannot fail by accident anymore ;o)


By the way, define what this means (by formula), Figure 8:
'a fill equal to the weighted average of the colors in the gradient vector'
- especially define in detail the weight factor (proportional to the radius
difference between to colours stops or to the area of between two stops?
else?)

And define an accuracy level for the question, whether the focal point
is on the circle or inside or outside, else the rules for the weight factor
remains for very exotic cases like fx="0" or fy="0", because for other
cases typically due numerical rounding issues the questionable 
corrected point will not be exactly on the circle.
Maybe even for fx="0" or fy="0" there will be rounding issues, if the
object or the gradient is somehow transformed.


Olaf
Received on Wednesday, 29 August 2012 12:21:01 GMT

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