Output transparent figures

[Arlindo da Silva]

On Wed, Jun 24, 2009 at 10:58 AM, Stephen R McMillan <
smcmillan at planalytics.com> wrote:

> Wang,
>
> Try using the "-t" (transparent) option with printim.  For example,
>
> 'printim image.png -t 0' should produce an image with a transparent
> background (assuming background is color 0).
>
> Reference from GrADS Documentation Index:
> http://grads.iges.org/grads/gadoc/gradcomdprintim.html
>
> Note:  I believe the transparent option will work only with versions 1.9 or
> later.
>

Recently Pablo Romero implemented additional transparency functionality in
the gxyat extension. For example, you can specify a transparency level for
each color with the set_rgba command extension.  You will need the latest
OpenGrADS bundle release available from http://opengrads.org. Notice that
you have to use "gxyat" instead of "printim" for enabling this feature; this
will also give you smoother fonts.   A manual page is built in:

ga-> set_rgba

NAME
     set_rgba - define color including alpha channel

SYNOPSIS
     set_rgba color red green blue alpha [mask]

DESCRIPTION
     This User Defined Command (UDC) defines *color* given its
     RGB triplet along with its *alpha* channel.

     color   integer in the range [16-255]
     red,
     green,
     blue    integers in the range [0-255]
     alpha   float, with alpha ranging from 0.0 (fully transparent)
             to 1.0 (fully opaque).

    The optional parameter *mask* determines whether the color below
    it is visible or not.

    mask=0  --- if alpha<1, *color* will be semi-transparent and the
                colors below it will be visible (default)
    mask=1  --- if alpha<1, *color* will be semi-transparent but the
                colors below it will *not* be visible

EXAMPLE
    In order to emulate the -t option in printim

       ga-> set rgb 60 125 125 125
       ga-> printim img.png -t 60

       Specify alpha=0 and mask=1

       ga-> set_rgba 60 125 125 125 0 1
       ga-> gxyat img.png



--
Arlindo da Silva
dasilva at alum.mit.edu
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