[mapserver-dev] RE: [UMN_MAPSERVER-DEV] Performance transparency

[thomas bonfort]

hi all,
code for AGG style level opacity is in the trunk (see
http://trac.osgeo.org/mapserver/ticket/1155 for limitations)
please report back if you see anything fishy going on...

On Fri, Mar 21, 2008 at 8:02 AM, Hallgren, Johan
<johan.hallgren at logica.com> wrote:
>  Have you seen any performance differences? I don't know if you have followed my question but the problem we had was that when the size of the image increased the performance decreased more than expected (when using transparency). We had a raster map in background and rendered a polygon layer on top. As you probably understand we need to see thru the polygons. We want to have the polygon layer semi transparent, like 40% transparent or so.
>
>  Do you think you work will affect us?

yes, you should gain performance-wise by using style rather than layer
level opacity.
you gain:
* creation of a temporary gd image (that's image_height mallocs the
way gd works)
* merging of the temporary image onto the main mapserver image
(width*height blending operations)
* destroying of the temp image

cheers.
thomas