In Chapter 12, Filters and Postprocessing Effects, we saw how the FogFilter class could be used to add a fog effect to the scene. It was also noted that those 3D objects that were behind the last layer of fog were not rendered at all, providing an increase in performance.
Two additional filters are also included in the away3d.core.filter package: MaxPolyFilter and ZDepthFilter. Neither adds a visual effect to the scene, but they can both be used to reduce the number of mesh elements that get drawn to the screen.
Both filters can be applied like the FogFilter class from Chapter 12, Filters and Postprocessing Effects, by assigning them to the filters property available on both the BasicRenderer and QuadrantRenderer classes. Or they can be passed into either the BasicRenderer or QuadrantRenderer constructors, with the resulting render class then assigned to the renderer property from the View3D class.
The ZDepthFilter class defines a maximum z depth for mesh elements. Those that lie beyond that maximum depth are not drawn to the screen. This provides the same performance benefits as the FogFilter class, but without the fog effect.
The ZDepthFilter constructor takes one parameter, maxZ, which defines the distance from the camera after which mesh elements are culled. In the following example, a new instance of the ZDepthFilter class has been created that will cull all mesh elements that are more than 200 units away from the camera.
var zDepthFilter:ZDepthFilter = new ZDepthFilter(200); view.renderer = new BasicRenderer(zDepthFilter);
Tip
In Away3D 3.6, there is a bug in the ZDepthFilter class that prevents it from working correctly. By using the FrustumClipping class, from the away3d.core.clip package, you can achieve the same visual effect as the ZDepthFilter class, but there is no performance benefit.
view.clipping = new FrustumClipping({maxZ:200});
The MaxPolyFilter filter will only allow a set number of mesh elements to be drawn to the screen. It does this by retaining only the specified number of mesh elements from the collection that would be drawn to the screen. Since this collection is sorted by depth, this has the effect of discarding those mesh elements that represented the furthest 3D objects in the scene.
The ZDepthFilter constructor takes one parameter, maxP, which defines how many mesh elements will be rendered. The following code creates a new instance of the MaxPolyFilter class that will draw only the closest 500 mesh elements.
var maxPolyFilter:MaxPolyFilter = new MaxPolyFilter(500); view.renderer = new BasicRenderer(maxPolyFilter);