Re: [Opengrads-devel] Partial transparency (alpha channel)

[Jennifer A. <jm...@co...>]

Hi, Arlindo --

On Nov 20, 2011, at 5:32 PM, Arlindo da Silva wrote:

> Brian, Jennifer:
>
>    In GrADS 2.1, would you consider extending "set rgb" to accept an  
> extra "alpha" channel? Since, you now use cairo for rendering,  
> taking advantage of the channel is really trivial, you can take a  
> look at what we did in gxyat. Partial transparency is very useful to  
> create plots like this one: 153722. If you wish I can contribute a  
> reference implementation once the 2.1 sources are available.
Brian did some testing with partial transparency using gd, and found  
some subtleties that we need to think about. I have some stand-alone  
code to handle semi-transparency in cairo, but we haven't integrated  
anything into the GrADS code base yet. We are still working on the  
changes to the structure of the metafile buffer, then we will add the  
new features on top of those changes.

>
>    We could also have gxyat built in (gxyat is nothing more than  
> "gxpng" modified to use cairo).  Because gd is much faster than  
> cairo, there always will be a place for printim as we know it, don't  
> you think?
The rendering with X11 will remain an option, as well as speedy  
generation of image output with the gd library via printim. But we are  
no longer going to support any metafile translators, so that we have  
the freedom to change the metafile structure without having to worry  
about supporting all the external utilities too. The ability to write  
out the contents of the metafile buffer to a file will be removed, so  
gxps, gxeps, gxtran, gxyat, and gv32.exe will all die with version  
2.1. The creation of all vector graphics output formats will only be  
supported inside GrADS via cairo.

--Jennifer