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

[Hallgren, Johan]

Hello

I have had a question last year related to performance when using transparency. Steve mentioned that there are plans to support feature-level transparency. Do we have any progress at that issue? When can I count on that feature?

/Johan



___________________________________



Johan Hallgren



Logica

Pelle Bergs backe 3

Box 1938, 791 19 Falun

Tel (och mobil): 023-547 46 (int: +46-2354746)

johan.hallgren at logica.com

http://www.logica.se



-----Original Message-----
From: UMN MapServer Developers List [mailto:MAPSERVER-DEV at LISTS.UMN.EDU] On Behalf Of Steve Lime
Sent: den 19 december 2007 20:31
To: MAPSERVER-DEV at LISTS.UMN.EDU
Subject: Re: [UMN_MAPSERVER-DEV] Performance transparency



Hi Johan: I've never quantified the performance hit but it is certainly expected. Layer-level transparency works like this:



  - a temporary image is created to render the transparent layer into, it is initialized to be completely transparent

  - rendering proceeds as normal in the temp image

  - the temp image is then "merged" into the base image, so for every non-transparent pixel in the temp image alpha blending is done and the base image pixel is modified

  - the temporary image is discarded



So, the processing time will increase with 1) image size and 2) vector layer density.



There are plans to support feature-level transparency but it won't work in all cases so layer level transparency will remain an option.



So, the results you are seeing are expected although I can't say if double is too much or not.



Steve





>>> On 12/19/2007 at 8:49 AM, in message

<D93CFEAA72FA764885CC1FDA94A1D89C035462F2 at WMRI000166.corp.wmdata.net>, Hallgren

Johan E <jhhal at WMDATA.COM> wrote:

> Hello Friends

>

> I a question regarding performance when using a transparent vectorlayer

> on top of a rasterlayer. The output is quite large (1400 * 1000 px) and

> vectordata is a shapefile with polygons.

>

> When turning the transparency on the vector layer the performance goes

> down quite much. It takes maybe double as long time to produce the map.

>

> Is there any knowledge about that?

>

> /Johan

>

> ___________________________________

>

>

> Johan Hallgren

>

> WM-data, Logica CMG

> Pelle Bergs backe 3

> Box 1938, 791 19 Falun

>

> Tel (och mobil): 023-547 46 (int: +46-2354746)

>

> johan.e.hallgren at wmdata.com

> <blocked::mailto:johan.e.hallgren at wmdata.com>

>

> http://www.wmdata.se

> <blocked::https://webaccess.wmdata.com/exchweb/bin/redir.asp?URL=http://

> www.wmdata.se/>

>

>
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