Opacity does not work

[idontgetoutmuch]

In this example all circles have the same opacity

import Diagrams.Prelude
import Diagrams.Backend.Postscript
import Diagrams.Backend.Postscript.CmdLine
import Data.Colour (withOpacity)

colors  = map (blue `withOpacity`) [0.1, 0.2 .. 1.0]
example = hcat' with { catMethod = Distrib, sep = 1 }
                (zipWith fcA colors (repeat (circle 1)))

main :: IO ()
main = defaultMain example

[byorgey]

This is a known problem, e.g. see the description at http://hackage.haskell.org/package/diagrams and also http://projects.haskell.org/diagrams/backend-tests/all-index.html . The problem is simply that Postscript does not support transparency, so there is no way for the diagrams-postscript backend to support the opacity attribute.

It would probably be good to document this better in the diagrams-postscript package itself. I will leave this ticket open for now as a reminder to improve the documentation.

[idontgetoutmuch]

Thanks for this. It is indeed documented but hard to find (or at least I didn't find it). It's not obvious how one could make it clearer though.

BTW with Safari the SVG output in http://projects.haskell.org/diagrams/backend-tests/all-index.html is messed up. I think this is a known issue. I can send a screenshot if necessary.

Dominic Steinitz
[email protected]
http://idontgetoutmuch.wordpress.com

On 14 Sep 2013, at 11:09, Brent Yorgey [email protected] wrote:

This is a known problem, e.g. see the description at http://hackage.haskell.org/package/diagrams and also http://projects.haskell.org/diagrams/backend-tests/all-index.html . The problem is simply that Postscript does not support transparency, so there is no way for the diagrams-postscript backend to support the opacity attribute.

It would probably be good to document this better in the diagrams-postscript package itself. I will leave this ticket open for now as a reminder to improve the documentation.

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[fryguybob]

I don't know how everyone feels about it but we could emit warnings on stderr when we encounter a color with transparency.