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http://www.openoffice.org/issues/show_bug.cgi?id=54144
Issue #:|54144
Summary:|Ellipsoid gradiens are not "ellipsoid"
Component:|Drawing
Version:|680m125
Platform:|All
URL:|
OS/Version:|All
Status:|UNCONFIRMED
Status whiteboard:|
Keywords:|
Resolution:|
Issue type:|DEFECT
Priority:|P3
Subcomponent:|viewing
Assigned to:|wg
Reported by:|haui
------- Additional comments from [EMAIL PROTECTED] Fri Sep 2 03:45:41 -0700
2005 -------
Ellipsoid gradients have their name from ellipsoids, which are affine images of
a sphere, haven't they? They are called ellipsoid gradients, because their color
isobars (lines of equal color) correspond to the isobars of an ellipsoid (lines
of equal height), aren't they? If this is the case, ellipsoid gradients are
broken.
The color isobars of "ellipsoid" gradients do not correspond to the isobars of
ellipsoids. I ever wondered, why these gradients look so strange in
(s|ooo)office, but I never found out why, until I now had a closer look at
gradients in general in the context of SVG import (Issue 2497). The document,
which I'll attach, shows that the color isobars of "ellipsoid" gradients in
(s|ooo)office correspond to the isobars of an object, that has the contour of an
ellipse, if looking from the top, but it has the contour of a diamond when
looking from left and right, and the contour of a doubled parallelogram, when
looking from front and back. Instead, the contours of ellipsoids are ellipses,
no matter from which side one looks.
The color isobars of ellipsoid gradients currently are ellipses, but ellipses
with varying eccentricity. This is not the case for isobars of ellipsoids.
Isobars of an ellipsoid are scaled versions (with constant aspect ratio) of the
contour ellipse. There are two mistakes: in the current implementation, both
axes (!) of the color isobar ellipses (instead of the scaling factor *1) are
varied linearly with the same slope (instead of elliptically *2). In
consequence, "ellipsoid" gradients are not even affine images of radial
gradients (what I would have expected). The attached document shows how to
construct a "truly" ellipsoid gradient.
*1) Scaling the outermost contour ellipse instead of varying its axes
with constant slope is a must to fix. It is the main reason, why
those gradients look so strange.
*2) Varying the color elliptically instead of linearly in optional
(IMO). When only two color stops are given in SVG, the color is
also varied linearly there. Of cause, elliptical variation (to get
a truly ellipsoid gradient) can be accomplished by providing
multiple color stops that approximate the contour of the color
ellipse.
This problem existed from the beginning of the time (in the beginning
StarDivision created StarOffice...). It was inherited by OpenOffice 1.0 and
handed down to OpenOffice 1.1 and 2.0 beta.
This is also an OpenDocument problem.
1) A problem of the specification, since it does not (to the best of
my knowledge) specify, how those "ellipsoid" gradients should look like.
2) A problem of compatibility with other OpenDocument applications.
Please, do not close this as WONTFIX, with the justification that is was so from
the beginning!
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