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Canvas MapStructure: Difference between revisions
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→SymbolLayer Controller
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For MultiSymbolLayers: this is also responsible for the searchCmd (mandatory!), which handles searching for the model objects used by symbols, and returns a current list of models. The models are compared to the previous list, and models are added/removed to match the new list. If custom equality comparison is needed (i.e. outside of <tt>id(a) == id(b)</tt>), set layer.searcher._equals(a,b) to an appropriate function during construction. | For MultiSymbolLayers: this is also responsible for the searchCmd (mandatory!), which handles searching for the model objects used by symbols, and returns a current list of models. The models are compared to the previous list, and models are added/removed to match the new list. If custom equality comparison is needed (i.e. outside of <tt>id(a) == id(b)</tt>), set layer.searcher._equals(a,b) to an appropriate function during construction. | ||
For SingleSymbolLayers: this is responsible for the mandatory getModel() to provide a model object. This is called once and used for the lifetime of the layer, so the object should be dynamic (this works particularly well with a simple property node that supplies position/latitude-deg + position/longitude-deg or latitude-deg + longitude-deg -- this can of course be extended, see [https://gitorious.org/fg/fgdata/source/4732a3b620cd0df36ebffdba76a3872c43539bf8:Nasal/canvas/MapStructure.nas#L243-246]). If the returned object has an update() method, this is called before the position is retreived. | |||
{{Note|the _equals line adds a new function to the layer's searcher hash - we need to provide a way to check for "equality", i.e. for navaids that could be position and/or the ID (name). For custom/new layers, we need to provide a custom equality check function. What you are doing there is just adding a custom equality check function that always returns "false" (not equal). This is used by MapStructure to "smartly" identify and differentiate between old and new objects, i.e. to reduce workload and improve performance - imagine the "FIX" layer, which may have hundreds of fixes - while flying, a few dozen will be "new" ones, while most others will be "old" - we'll only remove the old ones, and only add new ones. If the custom definition is not provided, you should get an error suggesting that you add a corresponding method so that the underlying logic can check all objects for equality - see the bottom of the MapStructure article for details, or search for "_equals"}} | {{Note|the _equals line adds a new function to the layer's searcher hash - we need to provide a way to check for "equality", i.e. for navaids that could be position and/or the ID (name). For custom/new layers, we need to provide a custom equality check function. What you are doing there is just adding a custom equality check function that always returns "false" (not equal). This is used by MapStructure to "smartly" identify and differentiate between old and new objects, i.e. to reduce workload and improve performance - imagine the "FIX" layer, which may have hundreds of fixes - while flying, a few dozen will be "new" ones, while most others will be "old" - we'll only remove the old ones, and only add new ones. If the custom definition is not provided, you should get an error suggesting that you add a corresponding method so that the underlying logic can check all objects for equality - see the bottom of the MapStructure article for details, or search for "_equals"}} | ||
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