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A point light's attenuation defines how bright it is with respect to its distance from objects. You can set a light's attenuation by using Ogre's Light::setAttenuation function. The function takes four Real parameters: Range, Constant, Linear, and Quadratic.

The Range parameter has nothing to do with the brightness. If an objects distance is greater than the range, the light has no effect on the object. If the object is in range, the light's effect is calculated with the following formulas:

• Luminosity = 1 / Attenuation

• Attenuation = Constant + Linear * Distance + Quadratic * Distance ^ 2

Picking the values by trial and error is time consuming and unintuitive. I have calculated some values for the parameters that work well for specified ranges. Using these numbers, the light has 100% intensity at 0 distance, and trails off to near black at a distance equal to the Range. Keep in mind that most of the light falls in the first 20% of the range.

Range Constant Linear Quadratic

3250, 1.0, 0.0014, 0.000007

600, 1.0, 0.007, 0.0002

325, 1.0, 0.014, 0.0007

200, 1.0, 0.022, 0.0019

160, 1.0, 0.027, 0.0028

100, 1.0, 0.045, 0.0075

65, 1.0, 0.07, 0.017

50, 1.0, 0.09, 0.032

32, 1.0, 0.14, 0.07

20, 1.0, 0.22, 0.20

13, 1.0, 0.35, 0.44

7, 1.0, 0.7, 1.8

For example, if you wish to have a light that gradually dims until it has no effect at distance 100:

```Light *light;                               //create pointer to light object
light = mSceneMgr->createLight("Light #1"); //set the pointer to a newly created light
light->setType(Light::LT_POINT);            // make this light a point light
light->setDiffuseColour(1.0, .5, 0.0);      //color the light orange
light->setSpecularColour(1.0, 1.0, 0.0);    //yellow highlights
light->setAttenuation(100, 1.0, 0.045, 0.0075);```

Once you have chosen a Range and corresponding values, you can tweak the Constant and Linear values.

Decreasing the Constant parameter toward 0.0 brightens the light, while increasing it dims the light.

Increasing the Linear parameter causes the light to fade more quickly with distance. I don't suggest changing the Quadratic value or decreasing the Linear values, as doing so will require you to recalculate the Range. Negative numbers are not allowed.

Finally, Decreasing the Range value may give your application a performance boost, but decreasing it too much will cause the object to noticeably change brightness when it moves out of range of the point light.

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Alias: Point_Light_Attenuation

Contributors to this page: Beauty  , OgreWikiBot  , JustBoo and jacmoe  .
Page last modified on Tuesday 22 of February, 2011 21:30:24 UTC by Beauty .