InstancedMeshGeometryVisual3D Class

InstancedMeshGeometryVisual3D is a WPF Visual3D object that can be used to define a MeshGeometry3D that will be rendered multiple times as instances where each instace can have its own color and its own world matrix (defines scale, rotation and translation).

When rendered with DirectX, InstancedMeshGeometryVisual3D provides the fastest way to render many MeshGeometry3D instances.

The MeshGeometry3D object that is rendered with this InstancedMeshGeometryVisual3D need to be specified in the InstancedMeshGeometryVisual3D constructor. In the constructor you can also specify the SpecularMaterial that can be used for all instances (but can be null).

The data about each instance that will be rendered are specified with InstancesData property. InstancesData is an array of InstanceData structs. Each InstanceData defines a Matrix and Color. Matrix can be used to position the object (by defining the M41, M42, M43 fields), scale of the object (by defining M11, M22, M33) and rotation (with using method on the Matrix class). Color defines the color of this instance - same as using DiffuseMaterial with SolidColorBrush. If color has alpha value less the 1 (is semi-transparent), then see below for more information on how to render semi-transparent objects.

To render back faces (back side of triangles) defined in the MeshGeometry3D, set the IsBackFaceMaterial to true.

By default the InstancedMeshGeometryVisual3D is not hit test visible - this means that by default you cannot use WPF hit testing or subscribe on mouse events (MouseOver, MouseClick, etc.) with EventManager3D from Ab3d.PowerToys. To enable hit testing, set the IsWpfHitTestVisible property to true.
IMPORTANT:
When IsWpfHitTestVisible is true then InstancedMeshGeometryVisual3D always creates WPF's GeometryModel3D objects (one for each instance) that are used by WPF's hit testing. This can greatly increase initialization time.

When GeometryModel3D objects are created with this InstancedMeshGeometryVisual3D, then a customInstanceIndexProperty property is set to each created GeometryModel3D object. This property can be read with using modelHit.GetValue(InstancedMeshGeometryVisual3D.InstanceIndexProperty) to get the instance index that was used to create the GeometryModel3D object.

When the values in the InstancesData are changed after the InstancedMeshGeometryVisual3D has been rendered, you need to call the Update or Update(Int32, Int32, Boolean) method (call the overload without parameters when data for all instances are changed, call Update with parameters when only some instances data are changed).

If you want to render many instances of Model3DGroup objects, you can use the InstancedModelGroupVisual3D.

When rendered with WPF, InstancedMeshGeometryVisual3D is rendered as multiple GeometryModel3D objects inside Model3DGroup.

Rendering semi-transparent instances

When instances use semi-transparent colors (color's alpha is less than 1), the UseAlphaBlend property must be set to true. This will use alpha bending to blend the semi-transparent colors with already rendered 3D objects.

If only some objects have transparent colors and the colors do not change, then it is recommended to split the instance objects into two InstancedMeshGeometryVisual3D objects - one with solid and the other with semi-transparent instances.

When rendering semi-transparent objects, you need to define the InstancedMeshGeometryVisual3D after opaque 3D objects (in the WPF's tree view). Note that TransparencyHelper from Ab3d.PowerToys does not work with InstancedMeshGeometryVisual3D - it always considers InstancedMeshGeometryVisual3D as opaque object.

Because semi-transparent objects are rendered with using alpha blending (blending semi-transparent color with already rendered objects), the order of positions need to be such, that the instances that farther away from the camera need to be added before those that are closer to the camera.

Reference