| 110 | 112 | Now let's take this example further. Suppose the feature source for your layer contains multiple geometry types: points, polylines, and polygons. You need to be able to control the stylization for each of these types. You have some predefined symbols you'd like to use for each type: a symbol with a !PointUsage for the points (symbol A), one with a !LineUsage for the polylines (symbol B), one with a !LineUsage for the polygon edges (symbol C), and a final one with an !AreaUsage for the polygon fill (symbol D). To configure your layer you create !SymbolInstances referencing each of these symbols. As described above, you set the !UsageType on each !SymbolInstance to remove any redundancy about which usage in the symbol definition should be active. Now the code starts drawing features from the layer. The only applicable symbol for point features is symbol A, so those features draw as expected. For polyline features we have a problem though: symbols A, B, and C can all be used to style polyline features. The active usage for symbol A is Point, and therefore we could draw a single instance of symbol A at the polyline mid-point. The active usages for symbols B and C is Line, and therefore we would use those symbols as line styles for that polyline. (The active usage for symbol D is Area, and that doesn't apply to polylines.) The same problem happens with polygon features: in this case all four symbols can be used to style polygon features. The basic problem here is that there's no place in the schema to specify which geometry type a symbol instance should apply to. There's no way for the code to automatically determine which symbols should be used for different geometry types. |
