[mapserver-dev] GSoC projects for MapServer?

thomas bonfort thomas.bonfort at gmail.com
Fri May 3 13:04:34 PDT 2013

On 3 May 2013 18:14, Daniel Morissette <dmorissette at mapgears.com> wrote:

> On 13-05-02 9:58 AM, thomas bonfort wrote:
>> Daniel,
>> A self contained project doable by a gsoc student could be the ability
>> to add blend modes (additive, soft-light, etc..) and layer filters (e.g.
>> blurring) to mapserver.
> I saw this too late for GSoC, but I would still be interested in seeing
> examples of how this would be used if you have some (I am not sure to
> understand the use case).

allowing to blur a layer would also allow for some cool effects, e.g. with
land that bleeds out with a halo effect into the ocean.

In terms of implementation, you first render the layer to a temporary,
initially transparent image buffer, as we are actually doing when using
layer level opacity. Once that image is rendered, you apply the transforms
to it while merging it into the final map image.
For this to be usefull, you have to be able to chain/apply different
transforms e.g. something like:

 name "land"
     #here we want to blur the rendered layer, and merge it with 30%opacity
using the soft light operator
     transform "blur type=gaussian radius=50"
     opacity 30
     composite "soft-light"
    #intentionally left empty, we want the normal layer to be rendered on
top of the blurred one

for an overview of the composition operators, you can have a look at
http://mapbox.com/tilemill/docs/guides/comp-op/#color_blending . Supporting
all of them is easy to implement as they are available in cairo and agg. In
practice, only a few would be really useful for cartography output (/me
forgets the famous "640k should be enough for everyone" quote :) )


> --
> Daniel Morissette
> http://www.mapgears.com/
> Provider of Professional MapServer Support since 2000
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