Builds a matrix that flattens geometry into a plane.

## Syntax

```
_Inout_  D3DXMATRIX *pOut,
_In_     const D3DXVECTOR4 *pLight,
_In_     const D3DXPLANE *pPlane
);

```

## Parameters

pOut [in, out]

Type: D3DXMATRIX*

Pointer to the D3DXMATRIX structure that is the result of the operation.

pLight [in]

Type: const D3DXVECTOR4*

Pointer to a D3DXVECTOR4 structure describing the light's position.

pPlane [in]

Type: const D3DXPLANE*

Pointer to the source D3DXPLANE structure.

## Return value

Type: D3DXMATRIX*

Pointer to a D3DXMATRIX structure that flattens geometry into a plane.

## Remarks

The D3DXMatrixShadow function flattens geometry into a plane, as if casting a shadow from a light.

The return value for this function is the same value returned in the pOut parameter. In this way, the D3DXMatrixShadow function can be used as a parameter for another function.

This function uses the following formula to compute the returned matrix.

```

P = normalize(Plane);
L = Light;
d = -dot(P, L)

P.a * L.x + d  P.a * L.y      P.a * L.z      P.a * L.w
P.b * L.x      P.b * L.y + d  P.b * L.z      P.b * L.w
P.c * L.x      P.c * L.y      P.c * L.z + d  P.c * L.w
P.d * L.x      P.d * L.y      P.d * L.z      P.d * L.w + d

```

If the light's w-component is 0, the ray from the origin to the light represents a directional light. If it is 1, the light is a point light.