Dear Kuba,
> There is a comment in svg.c that stipples are really just a fill-in for
> transparency:
>
> /* Since we can't do stipples in SVG, and since the whole stipple thing
> */
> /* was only put in because we can't (easily) do transparency effects */
> /* in X11, we convert stipples to transparency when the stipple is a */
> /* mask, and do a color blend with white when the stipple is opaque. */
>
> Since Qt has RGBA colors and you can paint with semi-transparent pens and
> brushes, should I just drop all stipple functionality and simply allow using
> arbitrary colors with arbitrary transparency for interior fills?
Yes, please do that.
> This would make the outline and interior color selection a little bit saner
> -- both
> would use a color list.
However, note that alpha transparency is not a PostScript option, so
correctly handling transparency in the display view is a step away from
WYSIWYG. However, in this day and age, writing on trees is not necessarily
the intended target, and perhaps it is more important to mainting
consistency between the screen view and the SVG format output.
> Now the usability options:
>
> 1. How is transparency (alpha value) shared?
> 1a. Fixed per-object alpha -- applies to both outline and fil.
> 1b. Outline and fill colors each have their own alpha.
> 1c. Only fill color has alpha, outline has fixed 100% opaqueness
I prefer method 1c, which is consistent with the existing use of
stipple patterns. If you make it easy for people to make semi-
transparent outlines, or mismatch outline and fill color, or boxes
with rounded edges, or every font ever invented, then people automatically
tend to go wild and produce the most horrid drawings that would make
Edward Tufte's hair curl. I prefer to make such things possible, but
difficult enough that it will coerce people into making simpler, sparer
drawings.
One could make an argument for transparent outlines, but the effect is
rather subtle and it doesn't seem to me necessary to provide the option.
> 2. How are the color lists handled?
> 2a. Separate fill and outline color lists.
> 2b. Shared fill and outline color lists.
Using the same arguments as above, option 2b is preferred.
> I presume that postscript supports transparency for both pens and brushes?
> I have a postscript greenbook somewhere IIRC, I have to find it :)
Display PostScript (DPS) might be able to deal with it (but nobody uses
DPS since the decline and fall of SunView), but standard PostScript
doesn't---a serious fault of Adobe's which I have never been able to
understand.
---Tim
+--------------------------------+-------------------------------------+
| Dr. R. Timothy Edwards (Tim) | email: [email protected] |
| Open Circuit Design, Inc. | web: http://opencircuitdesign.com |
| 22815 Timber Creek Lane | phone: (301) 528-5030 |
| Clarksburg, MD 20871-4001 | cell: (240) 401-0616 |
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