Lighting Equations (Windows Embedded CE 6.0)

1/6/2010

Microsoft® Direct3D® Mobile models illumination with equations that approximate the physics light. The lighting equations utilize the currently enabled lights, the current material parameters, the position of the viewer and the position of the vertex that is to be lit.

These equations describe a camera space implementation of Direct3D Mobile lighting. It is up to the driver implementation to decide which space to do lighting in, so long as the reformulation of the lighting equations produces the same results as the formulation listed in this section.

Notation

The following table shows the variables used in the lighting equations for vertex positions and properties.

Parameter	Default Value	Type	Description
Pe	(0,0,0)	D3DMVECTOR	Camera position in camera space.
Po	N/A	D3DMVECTOR	Position of current model origin (0,0,0,1) in the camera space, which is the fourth row of Mwv.
Mw	Identity	D3DMMATRIX	The current world matrix.
Mv	Identity	D3DMMATRIX	The current view matrix.
Mwv	Identity	D3DMMATRIX	The product of Mv and Mw.
La	(0,0,0,0)	D3DMCOLORVALUE	Global ambient color from the D3DMRS_AMBIENT render state (see D3DMRENDERSTATETYPE).
V	Not applicable	D3DMVECTOR	Vertex position in camera space.
N	Not applicable	D3DMVECTOR	Normalized vertex normal in camera space.
Vcd	0xFFFFFFFF (White)	D3DMCOLORVALUE	Vertex Diffuse Color.
Vcs	0x00000000 (Black)	D3DMCOLORVALUE	Vertex Specular Color.
Atten	(0,0,0,0)	D3DMCOLORVALUE	Light Attenuation.

The following table shows the variables used in the lighting equations for material properties.

Parameter	Default Value	Type	Description
Ma	Not applicable	D3DMCOLORVALUE	Ambient color of the material.
Md	Not applicable	D3DMCOLORVALUE	Diffuse color of the material.
Ms	Not applicable	D3DMCOLORVALUE	Specular color of the material.
Mp	0.0	Float	Specular power exponent of the material.

The following table shows the variables used in the lighting equations for the properties of light i. These variables correspond to the members of the D3DMLIGHT structure passed in calls to IDirect3DMobileDevice::SetLight.

Parameter	Default Value	Type	Description
Lpi	(0,0,0)	D3DMVECTOR	Light position in camera space.
Ldi	(0,0,1)	D3DMVECTOR	Light direction in camera space.
Lri	0.0	float	Light range distance.
Lcai	(0,0,0,0)	D3DMCOLORVALUE	Ambient color.
Lcsi	(0,0,0,0)	D3DMCOLORVALUE	Specular color.
Lci	(1,1,1,0)	D3DMCOLORVALUE	Diffuse color.
LAtt0i	0.0	float	Linear Attenuation Factor.
LAtt1i	0.0	float	Squared Attenuation Factor.
LAtt2i	0.0	float	Exponential Attenuation Factor.

The following list show the mathematical notations used to describe the lighting equations.

• ||V|| is the length of vector V.
• V1.V2 is the dot product of vectors V1 and V2.
• Norm(V) is the vector V, normalized.
• P1P2 is the vector from point P1 to point P2.
• M-1 is the inverse of matrix M.
• MT is the transpose of matrix M.
• V1/V2 is the vector where each component of V1 is divided by the corresponding component of V2.
• V1*V2 is the vector where each component of V1 is multiplied by the corresponding component of V2.

The following topics provide additional detail about the lighting equations.

• Camera Space Transformation
• Basic Lighting Formulas

See Also

Concepts

Lighting