ODF specification regarding multistop/-color gradients

[Regina Henschel]

Hi Heiko,

Heiko Tietze schrieb:
> Hello all,
>
> the LibreOffice conference gave me the chance to present some ideas regarding Draw and shapes in general. One of the most wanted features is the multistop gradient. Today we can define gradients between two colors, either linear, radial, or whatever. It would be nice to have a) non-linear multistop gradients, for example to illustrate a sundown with a small red and a larger yellow section, and b) a gradient over more than two colors, e.g. in order to add blue sky to the sundown.
>
> Since Calligra offers multicolor gradients, Armin and me checked how it is saved (the rendering is build-in right now). And it turns out that they hack SVG into the ODF.

That is no "hack SVG into ODF ". The feature "svg-gradient is in ODF 
from the beginning. In ODF 1.1 it is in "14.14.2 SVG Gradients", and in 
ODF 1.2 it is in 16.40.2<svg:linearGradient>, 
16.40.3<svg:radialGradient> and 16.40.4<svg:stop> and its attributes in 
chapter 19. Only OpenOffice.org had no implementation for it.

The request for LO is in
https://bugs.documentfoundation.org/show_bug.cgi?id=94588

  For the (predefined) rainbow-like gradient the style.xml looks like this:
>
> <svg:linearGradient draw:name="gradient1" svg:spreadMethod="pad" svg:x1="0.000000%" svg:x2="100.000000%" svg:y1="0.000000%" svg:y2="100.000000%">
> <svg:stop svg:offset="0" svg:stop-color="#ff0000"/><svg:stop svg:offset="0.183575" svg:stop-color="#ffe100"/><svg:stop svg:offset="0.347826" svg:stop-color="#00ff00"/><svg:stop svg:offset="0.516908" svg:stop-color="#00ffff"/><svg:stop svg:offset="0.68599" svg:stop-color="#0000ff"/><svg:stop svg:offset="0.845411" svg:stop-color="#ff00fb"/><svg:stop svg:offset="1" svg:stop-color="#ff0004"/>
> </svg:linearGradient>

A true "rainbow" is not possible, because that needs a HSB color model. 
So using stops is the only way to do it as SVG gradient. The quoted 
snippet is all valid ODF.

ODF has some restrictions compared to SVG. But starting with that, what 
is currently possible in ODF, would help a lot. And I personally see no 
problem in getting further SVG features into ODF1.3 if needed and an 
implementation exists.

>
> As an UX evangelist I don't care too much about the implementation

But I do. I prefer a solution with clean ODF.

Therefore I do not want an isolated, workaround solution for OOXML 
import as touched upon in 
https://bugs.documentfoundation.org/show_bug.cgi?id=76682 and was 
proposed in https://gerrit.libreoffice.org/#/c/12056/

  and have rather the workflow and interactions in mind.

It needs another UI. The linear bar as in PowerPoint is not the only 
possible solution. I like more the two dimensional way, where you define 
a way in a color area. (I just don't remember, where I saw it.)

  Ideally the multi-gradient works with all features, and not as another 
type next to linear, radial etc. (There might be a problem that result 
in this sub-optimal solution).

It is another kind of gradient. The <draw:gradient> kind 'rectangle' and 
'square' are not possible with SVG.

>
> And finally we have to take interoperability into account as well as the conformity to the ODF specs (no idea if and how it is defined).

See above.

>
> So how do we make multistop/multicolor gradients possible?

There exists already rendering solutions in rendering SVG-images.


>
> Cheers,
> Heiko
>
> PS: Suggestions on how to implement this feature in the UI are existing.

Where?

Kind regards
Regina