transparent hatch

[Frank Warmerdam]

On 8/4/05, Richard Greenwood <richard.greenwood at gmail.com> wrote:
> Since Mapserver 4.4, when I want to output jpegs, if I want a simple
> vector hatch to be transparent (for underlying layer to show thru) I
> have to set IMAGEMODE PC256:
> 
> OUTPUTFORMAT
>   NAME jpeg
>   DRIVER "GD/JPEG"
>   MIMETYPE "image/jpeg"
>   IMAGEMODE PC256
>   EXTENSION "jpg"
> END
> 
> If I use IMAGEMODE RGB, the space between the vector lines is opaque white.
> 
> My symbol definition:
> 
> Symbol
>         NAME 'Diag_NE_SW'
>         TYPE VECTOR
>         POINTS
>                 0 1
>                 1 0
>         END
> END
> 
> And my class definition:
> 
> CLASS
>         NAME "FEMA 500 Year Flood Zone SHX"
>         EXPRESSION 'SHX'
>         STYLE
>                 COLOR 112 186 248
>                 OUTLINECOLOR 0 0 255
>                 SYMBOL 'Diag_NE_SW'
>                 SIZE 20
>         END
> END
> 
> Am I overlooking anything? I would prefer to use IMAGEMODE RGB.

Rich, 

Try adding a "TRANSPARENT ALPHA" line in your layer definition.
Amoung other things this enables the alpha blending needed for
raster symbols with transparency.  

I'm not really satisfied with this requirement, though it is organized
this way partly to avoid extra work in the common case where there
is no transparency.

Best regards,

-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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and watch the world go round - Rush    | Geospatial Programmer for Rent