[Thuban-list] RFC: Layer Rendering

[Jan-Oliver Wagner]

we discussed this IRL.

Currently the Layers should neither know how to store itself in
a file nor should it do the rendering.

Layer currently is a quite stupid class that just
holds the necessary information. Storing the infos to a file is
kept central in order to have a central point where different file formats
(or specific versions of the same format) are be read/written.
A single object (like Layer) does not know about the file format in
general and thus should not write small portions of it.

For the time being, we also keep the rendering in place, but this might
eventually change.

On Thu, Jan 16, 2003 at 11:16:25AM +0100, Jonathan Coles wrote:
> I've noticed that the MapRenderer class contains all the logic to draw
> the layers and shapes. I think that most of this can and should be moved
> to another class, either Layer or LayerRenderer. When work on the layer
> classification begins (see RFC: Layer Classification) there will need to
> be a lot of type checking to determine what kind of shape is being
> drawn, what shape property is being used for classification, and so on.
> A function like layer.render(dc, ...). would clean a lot of this up and
> just let the system handle what Layer to draw. 
> 
> Which leads into creating several subclasses of Layer for each type.
> Each subclass would know how to draw itself and what data values are
> stored in its classification data structure. This allows new types of
> Layers to be drawn more easily. Ideally, Layers would know how to load
> and save themselves (although the exact hierarchy for this needs some
> thought; I wouldn't want to overload the class with too much work). It
> seems that Layers do know how to load themselves, but a different class
> is saving them. Putting all this is the same or related class has the
> advantage of easily adding Layers that are stored in different formats.
> Perhaps Layer loading could be a plug-in feature (I believe that this is
> easy to do in Python?). 

-- 
Jan-Oliver Wagner               http://intevation.de/~jan/

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