Microsoft DirectX 9.0

Ambient Lighting

Ambient lighting provides constant lighting for a scene. It lights all object vertices the same because it is not dependent on any other lighting factors such as vertex normals, light direction, light position, range, or attenuation. It is the fastest type of lighting but it produces the least realistic results. Microsoft?Direct3D?contains a single global ambient light property that you can use without creating any light. Alternatively, you can set any light object to provide ambient lighting. The ambient lighting for a scene is described by the following equation.

Ambient Lighting = Ca*[Ga + sum(Lai*Attenuationi*SpotFactori)]

Formula for ambient lighting is incorrect. It should be Ambient Lighting = Ca*[Ga + sum(Lai)*Atti*Spoti] Where Att and Spot are attenuation and spot factors, computed for i-light.

The parameters are defined in the following table.

ParameterDefault valueTypeDescription
Ca(0,0,0,0)D3DCOLORVALUEMaterial ambient color.
Ga(0,0,0,0)D3DCOLORVALUEGlobal ambient color.
sumN/AN/ASummation of the ambient light from the light objects.
Lai(0,0,0,0)D3DVECTORLight ambient color of the ith light.
Atteni(0,0,0,0)D3DCOLORVALUELight attenuation of the ith light. See Attenuation and Spotlight Factor.
Spoti(0,0,0,0)D3DVECTORSpotlight factor of the ith light. See Attenuation and Spotlight Factor.

The value for Ca is either:

Note  If either AMBIENTMATERIALSOURCE option is used, and the vertex color is not provided, then the material ambient color is used.

To use the material ambient color, use SetMaterial as shown in the example code below.

Ga is the global ambient color. It is set using SetRenderState(D3DRENDERSTATE_AMBIENT). There is one global ambient color in a Direct3D scene. This parameter is not associated with a Direct3D light object.

Lai is the ambient color of the ith light in the scene. Each Direct3D light has a set of properties, one of which is the ambient color. The term, sum(Lai) is a sum of all the ambient colors in the scene.


In this example, the object is colored using the scene ambient light and a material ambient color. The code is shown below.

#define GRAY_COLOR			0x00bfbfbf

// create material
ZeroMemory( &mtrl, sizeof(mtrl) );
mtrl.Ambient.r = 0.75f;
mtrl.Ambient.g = 0.0f;
mtrl.Ambient.b = 0.0f;
mtrl.Ambient.a = 0.0f;
m_pd3dDevice->SetMaterial( &mtrl );
m_pd3dDevice->SetRenderState( D3DRS_AMBIENT, GRAY_COLOR);

According to the equation, the resulting color for the object vertices is a combination of the material color and the light color.

These two images show the material color, which is gray, and the light color, which is bright red.

Gray sphere?img alt="Red sphere" src="../../../../../Art/LightRed.jpg">

The resulting scene is shown below. The only object in the scene is a sphere. Ambient light lights all object vertices with the same color. It is not dependent on the vertex normal or the light direction. As a result, the sphere looks like a 2-D circle because there is no difference in shading around the surface of the object.

Sphere with ambient lighting

To give objects a more realistic look, apply diffuse or specular lighting in addition to ambient lighting.

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