[Mapserver-users] alpha blending

Frank Warmerdam warmerdam at pobox.com
Tue May 11 16:02:59 EDT 2004

bartvde at xs4all.nl wrote:
> Hi list,
> what are the current alpha blending capabilities of Mapserver?
> I saw an e-mail from Frank Warmerdam from 2002 in which he states:
> "I would like to see Map file color keywords be able to specify an RGBA
> color, instead of just RGB but even then alpha blending can only practically
> be done on 24bit output, not colormap output files."
> But AFAIK nothing has been pursued in this direction. The current state of
> GD would make this possible.
> So my impression is that alpha blending is only possible for raster layers
> at the moment and not for vector layers. Is this impression correct? Are
> there any plans to support the RGBA colors in the MAP file?


As far as I know Paul is right.  Transparency/alpha blending is currently
only supported at the layer level for all layers types "TRANSPARENCY" keyword,
and for rasters via various mechanisms.  I am not aware of any plans to extend
the colorObj and .map file to handle alpha values though I still think it is
a natural idea.

Perhaps Tyler-the-poll-meister will do a poll on most-wanted-new-snazzy-feature
and include full alpha support as an option.

Best regards,

I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent

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