PlanarShadowRenderingProvider Class

PlanarShadowRenderingProvider provides support for rendering shadows on a 3D plane surface.

Its advantage over VarianceShadowRenderingProvider is that it can render sharp shadows that do not loose precision even when user zoom into the shadow. It is also much faster to render. The shadows are rendered with applying a shadow matrix to all objects. This matrix flatten all the objects so that they have no height and become only a 2D shape of the object's shadow. That shape is then rendered a 3D object on top of the plane.

To support clipping to plane's bounds by the GPU (when using Ab3d.PowerToys this need to be done in software) and to prevent rendering some parts of the shadow multiple times, a DirectX stencil buffer is used.

Disadvantages of VarianceShadowRenderingProvider are:
- it can render shadows only to a 3D plane,
- it cannot render soft shadows,
- shadows are rendered for object behind the plane or point light,
- some objects that lie on the plane or are very close to the plane may get slightly invalid shadow.

It is also possible to render planar shadows without PlanarShadowRenderingProvider and with using only PlanarShadowMeshCreator from Ab3d.PowerToys but this does not provide hardware accelerated shadows rendering (shadow object need to be created on the CPU) and cannot render transparent shadows correctly - see samples that come with Ab3d.PowerToys.

PlanarShadowRenderingProvider support only directional or point light as source of the shadow. To use a custom light that does not illuminate the 3D scene set the CustomShadowLight property. Otherwise, the first light that has DXAttributeType.IsCastingShadow attribute set to true is used. If no light has IsCastingShadow attribute set, then the first directional or point light is used.

PlanarShadowRenderingProvider also renders the 3D plane that receives the shadow. If you want to render your the plane by yourself, then set ShadowPlaneMaterial and ShadowPlaneBackMaterial to null. But you must still provide ShadowPlaneSize (and ShadowPlaneCenterPosition, ShadowPlaneNormalVector and ShadowPlaneHeightDirection when they differ from default values). This is needed to correctly set the stencil buffer to clip shadow to the plane's area. If ShadowPlaneSize is set to (0,0) them the shadow plane will not be rendered and the shadow will not be clipped by the PlanarShadowRenderingProvider.

Example

// Create new PlanarShadowRenderingProvider
var planarShadowRenderingProvider = new PlanarShadowRenderingProvider()
{
    ShadowPlaneCenterPosition = new Vector3(0, 0, 0),
    ShadowPlaneSize = new Vector2(400, 400),
    ShadowPlaneNormalVector = new Vector3(0, 1, 0),
    ShadowPlaneHeightDirection = new Vector3(0, 0, -1),

    ShadowPlaneMaterial = new StandardMaterial()
    {
        DiffuseColor = Colors.Green.ToColor3()
    },

    ShadowPlaneBackMaterial = new StandardMaterial()
    {
        DiffuseColor = Colors.DimGray.ToColor3()
    },

    ShadowColor = Color3.Black,
    ShadowTransparency = 0.65f,

    // Because shadow is rendered as standard 3D object, we need to offset it from the shadow plane
    // to prevent z-fighting problems that occur when two 3D objects are rendered to the same 3D position.
    // This value need to be very small so that it is not seen that the shadow is above the plane.
    // Default value is 0.01f.
    ShadowOffsetFromPlane = 0.01f,

    // When using PlanarShadowRenderingProvider we do not need PlanarShadowMeshCreator from Ab3d.PowerToys
    // to prepare a special MeshGeometry3D for us. Also PlanarShadowMeshCreator does not need to manually (on the CPU)
    // cut the shadow to the plane bounds but this can be done with using hardware accelerated algorithm (using stencil buffer).
    // But if we still want to use PlanarShadowMeshCreator we can set the following two properties to false 
    // (for example if we wanted to use PlanarShadowRenderingProvider just to provide proper transparent shadows).
    ApplyShadowMatrix = true,
    CutShadowToPlaneBounds = true,

    // To use a custom light that does not illuminate the 3D scene set the CustomShadowLight.
    // Otherwise the first light that has DXAttributeType.IsCastingShadow attribute set to true is used.
    // If no light has IsCastingShadow attribute set, then the first directional or point light is used.
    //CustomShadowLight = new Ab3d.DirectX.Lights.DirectionalLight(new Vector3(0, -1, 1))
    //CustomShadowLight = new Ab3d.DirectX.Lights.PointLight(new Vector3(0, 500, 0), 300)
};

// Initialize shadow rendering with DXEngine
MainDXViewportView.DXScene.InitializeShadowRendering(planarShadowRenderingProvider);

Reference