FW: transparent images using visad?

Hello all,

apologies - forgot to cc the list.


-----Original Message-----
From: Jim Koutsovasilis 
Sent: Tuesday, July 18, 2006 11:08 AM
To: 'Stuart Maclean'
Subject: RE: transparent images using visad?

Hello Stuart,

I haven't used VisAD in a while, but I remember that you need to add a
Display.Alpha scalar map to the display - this scalar map would then map
the alpha-values of your image to transparency on the screen. Can you
include the VisAD code you are using to add the scalar maps to the 2D


-----Original Message-----
From: owner-visad@xxxxxxxxxxxxxxxx [mailto:owner-visad@xxxxxxxxxxxxxxxx]
On Behalf Of Stuart Maclean
Sent: Tuesday, July 18, 2006 10:53 AM
To: visad@xxxxxxxxxxxxxxxx
Subject: transparent images using visad?

I am trying to use visad in a web app (Java servlets) to produce
transparent png responses. I build the DisplayImplJ2D in OFFSCREEN mode.

  I serialize to png using the javax.imageio.ImageIO routines.  For now,
the only data is a UnionSet of points, representing a 'route'.

  I cannot get the call to DisplayImplJ2D.getImage to produce a
'transparent' image.  I have replaced all calls in VisADCanvas2D which
build BufferedImage of type TYPE_INT_RGB with TYPE_INT_ARGB.  Maybe this
could be an options in future releases (??)

When I get the BufferedImage back from the call to
DisplayImplJ2D.getImage(true), it claims to have given me an ARGB type
of BufferedImage (using getType()) but when I view it I get a filled in
background color.

If  I replace the visad code in my servlet with this, I get a nice
transparent image (via the ImageIO calls):

        BufferedImage br = new BufferedImage( 500, 500,
BufferedImage.TYPE_INT_ARGB );
                Graphics2D g = br.createGraphics();
                g.setBackground( new Color( 0, 0, 0, 0 ) );
                g.setColor( Color.RED );
                g.clearRect( 0, 0, 500, 500 );
                g.drawLine( 100, 100, 200, 200 );

So some Visad code must be doing some other operation(s) to 'ruin' the
transparency of the composed BufferedImage ?? I have looked in
VisADCanvasJ2D somewhat but nothing is jumping out at me.

I confess I am no expert in graphics nor graphics files.

BTW: The underlying approach here is to use Visad as a 'data/map server'

which will produce one 'layer' of data in each image, e.g. a basemap or
a route or some other plot.  I am then using a web browser/Javascript's
z ordering to compose the whole 'picture'.  I have an app where the UI
must be a browser, so i cannot go with a jnlp solution.  If all goes
well, I will write up the architecture and post here.  As you can
imagine, I am stuck w/out transparent images.

Any help gratefully appreciated


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