D3DXSHEvalDirectionalLight function (D3dx9math.h)

Evaluates a directional light and returns spectral spherical harmonic (SH) data.


HRESULT D3DXSHEvalDirectionalLight(
  _In_        UINT        Order,
  _In_  const D3DXVECTOR3 *pDir,
  _In_        FLOAT       RIntensity,
  _In_        FLOAT       GIntensity,
  _In_        FLOAT       BIntensity,
  _Out_       FLOAT       *pROut,
  _Out_       FLOAT       *pGOut,
  _Out_       FLOAT       *pBOut


Order [in]

Type: UINT

Order of the SH evaluation. Must be in the range of D3DXSH_MINORDER to D3DXSH_MAXORDER, inclusive. The evaluation generates Order² coefficients. The degree of the evaluation is Order - 1.

pDir [in]

Type: const D3DXVECTOR3*

Pointer to the (x, y, z) hemisphere axis direction vector in which to evaluate the SH basis functions. See Remarks.

RIntensity [in]


The red intensity of the light.

GIntensity [in]


The green intensity of the light.

BIntensity [in]


The blue intensity of the light.

pROut [out]

Type: FLOAT*

Pointer to the output SH vector for the red component.

pGOut [out]

Type: FLOAT*

Optional pointer to the output SH vector for the green component.

pBOut [out]

Type: FLOAT*

Optional pointer to the output SH vector for the blue component.

Return value


If the function succeeds, the return value is D3D_OK. If the function fails, the return value can be: D3DERR_INVALIDCALL.


The output vector is computed so that if the intensity ratio R/G/B is equal to 1, the resulting exit radiance of a point directly under the light on a diffuse object with an albedo of 1 would be 1.0. This will compute three spectral samples; pROut will be returned, while pGOut and pBOut may be returned.

On the sphere with unit radius, as shown in the following illustration, direction can be specified simply with theta, the angle about the z-axis in the right-handed direction, and phi, the angle from z.

illustration of a sphere with unit radius

The following equations show the relationship between Cartesian (x, y, z) and spherical (theta, phi) coordinates on the unit sphere. The angle theta varies over the range of 0 to 2 pi, while phi varies from 0 to pi.

equations of the relationship between cartesian and spherical coordinates


Requirement Value

See also

Math Functions

Precomputed Radiance Transfer (Direct3D 9)