Re: [udig-devel] Question on Renderers

["Ugo Taddei" <ugo.taddei@xxxxxxxxxxxxxxxxxx>]

Hello, Emily,

Emily Gouge said:
> Ugo,
>
> Here is my attempt to explain some of the rendering stuff.
>
> Renderers are responsible for drawing data on an image.  Each Renderer
> has a RenderMetrics which is used to determine "how well" the
> corresponding renderer can render a given georesource.  The
> RenderMetricsFactories are used to create the RenderMetrics.
>
> Udig uses all this information to draw layers on the map.  When UDig
> opens a map it gets a list of all available RenderMetricsFactories by
> processing the extension point.
>
> When it goes to render a given layer (for example a shapefile layer); it
> goes though all the possible rendermetricsfactories; creates render
> metrics; and then rates the render metrics based on the information
> provided in that class.  Then the render metrics with the highest rating
> is used to create a renderer for that given layer.  (Some of this
> information is cached; so all this processing does not necessarily
> happen for each draw).
>
> So a layer can have multiple renderer, but by using the render metrics
> uDig determines which one to use.  In uDig there are multiple renderers
> that can render a shapefile: BasicFeatureRenderer and
> ShapefileFeatureRenderer; however because of the way the render metrics
> are set up for a shapefile the ShapefileFeatureRenderer will be picked
> over the other renderer to render shapefiles.
>
>
>  >I cannot see any other renderes.

Thanks for the explanation.
>
> My first guess would be to ensure the plug-ins for all renderers are
> included when you run your project.  If the RenderMetricFactories are
> not included when running then uDig won't know about them and won't be
> able to find any render metric factories when processing the extension
> point.

I think you hit the point, again ;-)

It was my service not being able to process the extension point for the
shapefile renderer. Meanwhile it's running again.

>
> I hope this is of some help.

Yes, off course!

>
> Emily
>

Cheers,

Ugo
>
>
> Ugo Taddei wrote:
>> Hello,
>>
>> I'm hopelessly trying to understand the rationale behind all those
>> Renderers, RenderMetrics and RenderMetricsFactories. For that, I've
>> adapted the code from StaticGISWidget and I'm trying to render onto an
>> image I created.
>>
>> I use ApplicationGIS.drawMap( drawParameters ) to render the image. It's
>> not working because
>>
>> Renderer renderer = decisive.getRenderer(context); (around line 855)
>>
>> returns a net.refractions.udig.project.internal.render.impl.PlaceHolder,
>> which apparently is some sort of dummy renderer, that is, does nothing.
>>
>> In my application I read a project, and try to render a map (with the
>> adapted code from StatcGisWidget). In the printlns I added, I only see a
>> MapGraphicRenderMetricsFactory (which I assume is always there, as I
>> don't have explicitely instantiated on or created one within the
>> project). I cannot see any other renderes.
>>
>> How does udig figures out, what sort of layer it has, say a shapefile,
>> and when does it do that?
>>
>> What renderer is responsible for the shapefiles, is it
>> ShapefileFeatureRenderer?
>>
>> Do I have to set the renderer myself?
>>
>> Thanks in advance,
>>
>> Ugo
>>
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