D3DXSHEvalHemisphereLight
Microsoft DirectX 9.0 SDK Update (October 2004)

D3DXSHEvalHemisphereLight Function


Evaluates a light that is a linear interpolation between two colors over the sphere.

Syntax

HRESULT WINAPI D3DXSHEvalHemisphereLight(      

    UINT Order,     const D3DXVECTOR3 *pDir,     D3DXCOLOR Top,     D3DXCOLOR Bottom,     FLOAT *pROut,     FLOAT *pGOut,     FLOAT *pBOut );

Parameters

Order
[in] Order of the spherical harmonic (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] Pointer to the (x, y, z) hemisphere axis direction vector in which to evaluate the SH basis functions. See Remarks.
Top
[in] The sky color.
Bottom
[in] The ground color.
pROut
[in] Pointer to the output SH vector for the red component.
pGOut
[in] Pointer to the output SH vector for the green component.
pBOut
[in] 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.



Remarks

The interpolation is done linearly between the two points, not over the surface of the sphere (that is, if the axis was (0,0,1) it is linear in Z, not in the azimuthal angle). The resulting spherical lighting function is normalized so that a point on a perfectly diffuse surface with no shadowing and a normal pointed in the direction pDir would result in exit radiance with a value of 1 (if the top color was white and the bottom color was black). This is a very simple model where Top represents the intensity of the "sky" and Bottom represents the intensity of the "ground."

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

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.

Function Information

Headerd3dx9math.h
Import libraryd3dx9.lib
Minimum operating systems Windows 98

See Also

Precomputed Radiance Transfer


© 2004 Microsoft Corporation. All rights reserved.
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