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Custom Style Renderers

Summary

Mapsui 2.0 supports custom style renderers. This means a user can create a custom style and associate this with a custom style renderer to allow full freedom in rendering a feature the way the user would like.

How it works

  • Create a custom style by deriving a class from IStyle.
  • Assign that style to an ILayer.Style or IFeature.Styles.
  • Create a custom renderer by deriving a class from ISkiaStyleRenderer and implement the Draw method.
  • Register the association of the custom style to the custom style renderer as in the line below. The consequence will be that if the Mapsui renderer detects this style it will call the Draw method on the style renderer.

This is how you register the association of a custom style to a custom style renderer

mapControl.Renderer.StyleRenderers.Add(typeof(CustomStyle), new SkiaCustomStyleRenderer());

This is the ISkiaStyleRenderer interface that you need to implement:

public interface ISkiaStyleRenderer : IStyleRenderer
{
  bool Draw(SKCanvas canvas, IReadOnlyViewport viewport, ILayer layer, IFeature feature, IStyle style, ISymbolCache symbolCache);
}

The IFeature has a Geometry field. The renderer is responsible to cast the IFeature.Geometry to the type it intends to render. The IStyle is the custom style the user defined. It could contain extra style information not present in the default style classes. The user will need to cast that IStyle to the custom style to use this extra information.

Code sample

Look in the Mapsui source code for CustomStyleSample.cs.

custom stye renderer

This is the most relevant code. In this sample the custom style contains no extra information, it is just an indication to use the associated custom renderer. It would be possible to add extra field like EarColor and NoseSize to the custom style which could be used in the renderer.

Remarks

Note, that the renderer depends on the technology we use for the rendering implementation which is SkiaSharp. Theoretically we could change this implementation or add other implementations but there are no plans for that.