History: -Point Light Attenuation

Source of version: 6 (current)

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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~np~^~/np~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
^

{img src="img/wiki_up/Attenuation_Graph.jpg" alt="Attenuation_Graph.jpg"}

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

{CODE(wrap="1", colors="c++")} 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);{CODE}

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.

!!See also
* ((-Light|Light))
* ((Light Attenuation Shortcut)) - code snippet
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{INCLUDE(page="ogrelex ext tpl")/}
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Alias: (alias(Point_Light_Attenuation))
History: -Point Light Attenuation

Source of version: 6 (current)

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