Constant-Linear-Quadratic Falloff: Difference between revisions
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===Introduction=== | ===Introduction=== | ||
While light travels from its source, it usually diminishes in intensity, limiting the area that its source can illuminate. This diminishing is called "light attenuation" or "fall-off". | |||
The | The attenuation of a normal, unmodified light entity is preset to be 100% quadratic. While this is typical real world attenuation, this rate is often too fast for virtual environments, creating unnatural glares on nearby textures (like the ceiling). | ||
The Constant-Linear-Quadratic system is an old system for adjusting how a light attenuates (or "falls off"). It has since been superseded by the two "percent falloff distance" keyvalues, which some may find easier to understand and handle. | |||
The ratio between the three keyvalues ''Constant'' (''_constant_attn''), ''Linear'' (''_linear_attn'') and ''Quadratic'' (''_quadratic_attn'') will determine the way in which the light attenuates. (The three values has gotten their names from the mathematical function used to describe the decline of its intensity.) | |||
===Constant Attenuation=== | |||
The | [[Image:ConstantLight.jpg|Constant attenuation|200px|right]] | ||
The picture on the right shows a lightsource displaying the simplest of attenuations: Constant attenuation. The keyvalues ''Constant'', ''Linear'' and ''Quadratic'' have here been set to "1", "0" and "0" respectively, creating a Constant-Linear-Quadratic ratio of 1:0:0, meaning that the attenuation is 100% Constant, 0% Linear, and 0% Quadratic. | |||
The 100% constant attenuation will result in a light that has no attenuation at all. The intensity, represented by the brigtness setting of the light entity, will be totally unaffected by distance, continuing until it hits a surface, theoretically capable of illuminating an infinite area. | |||
This type of light can be seen from the sky (sunlight, monlight and starlight), and other large and distant light sources. | This type of light can be seen from the sky (sunlight, monlight and starlight), and other large and distant light sources. | ||
As a 100% constant lightsource is an extreme type of light, constant light is mostly used in combination with the other two types of | As a 100% constant lightsource is an extreme type of light, constant light is mostly used in combination with the other two types of attenuations, to "soften" or limit them. | ||
{{clr}} | {{clr}} | ||
===Linear | ===Linear Attenuation=== | ||
[[Image:LinearLight.jpg|Linear | [[Image:LinearLight.jpg|Linear attenuation|200px|right]] | ||
This is the same light entity, but at a 0:1:0 ratio, making its lighting 100% linear instead. | This is the same light entity, but at a 0:1:0 ratio, making its lighting 100% linear instead. | ||
Mathematically, the decline of this type of light is linear, inversely proportial to the distance from the light source (I = 1/d). | Mathematically, the decline of this type of light is linear, inversely proportial to the distance from the light source (I = 1/d where I is intensity and d is distance). This means that the light intensity (set by its brightness) will diminish (at a fixed rate) as it travels from its source. To compensate for this decline, Valve has boosted the intensity of the lightsource to 100 times its brightness. | ||
In the ''real'' world a 100% linear lightsource would be practically impossible, as it would represent a real world soft light of ''infinite'' size, but in the ''virtual'' world, a 0:1:0 lightsource is believable for most entity based lightsources. | |||
{{clr}} | {{clr}} | ||
===Quadratic | ===Quadratic Attenuation=== | ||
[[Image:QuadraticLight.jpg|Quadratic | [[Image:QuadraticLight.jpg|Quadratic attenuation|200px|right]] | ||
This is a normal, unmodified light source, preset to 0:0:1, making it 100% Quadratic. | This is a normal, unmodified light source, preset to 0:0:1, making it 100% Quadratic. | ||
Mathematically, the attenuation of a 100% quadratic light is exponential (quadratic), expressed as "I = 1/d^2", meaning that the further the light travels from its source, the ''more'' it will be diminished. This creates a very sharp drop in light. To compensate for the fast decline of quadratic lights, Valve has boosted the intensity of them to be 100^2 (10 000) times more intense than the actual intensity. | |||
An unmodified (100% quadratic) lightsource represents a pure "point light source", | An unmodified (100% quadratic) lightsource represents a pure "point light source" in the real world. In the virtual world, this effect looks like a lightsource shining through murky water, looking far from typical real world lightsource behavior. | ||
When used | When used in moderation, quadratic attenuation can be used not only for small lightsources, but also to reflect light travelling through something more dispersing than air, like air humidity (like fog) or water. | ||
{{clr}} | {{clr}} | ||
=== | ===Mixing Attenuation=== | ||
When blending between these three types of | When blending between these three types of attenuation, you set the proportions of each attenuation type against the other two types. To avoid confusion, keep in mind that you can set the scale of these proportions as you wish: A proportion of 3:6:1 gives the exact same result as 6:12:2, or 30:60:10, which can easily be translated to 30%, 60% and 10%. | ||
=== | ===External links=== | ||
*[http://www.editlife.net/tutorials.php?id=15 A more in-depth explanation of the Hammer system.] | |||
*[http://www.izware.com/mirai/tips/light-attenuation/light-attenuation.pdf A lenghty explanation from the manual of the Mirai program.] | |||
*[[wikipedia:Soft_light|The little I could find about falloff on Wikipedia.]] | |||
[[Category:Level Design]] | [[Category:Level Design]] | ||
Revision as of 05:00, 19 August 2007
Introduction
While light travels from its source, it usually diminishes in intensity, limiting the area that its source can illuminate. This diminishing is called "light attenuation" or "fall-off".
The attenuation of a normal, unmodified light entity is preset to be 100% quadratic. While this is typical real world attenuation, this rate is often too fast for virtual environments, creating unnatural glares on nearby textures (like the ceiling).
The Constant-Linear-Quadratic system is an old system for adjusting how a light attenuates (or "falls off"). It has since been superseded by the two "percent falloff distance" keyvalues, which some may find easier to understand and handle.
The ratio between the three keyvalues Constant (_constant_attn), Linear (_linear_attn) and Quadratic (_quadratic_attn) will determine the way in which the light attenuates. (The three values has gotten their names from the mathematical function used to describe the decline of its intensity.)
Constant Attenuation
The picture on the right shows a lightsource displaying the simplest of attenuations: Constant attenuation. The keyvalues Constant, Linear and Quadratic have here been set to "1", "0" and "0" respectively, creating a Constant-Linear-Quadratic ratio of 1:0:0, meaning that the attenuation is 100% Constant, 0% Linear, and 0% Quadratic.
The 100% constant attenuation will result in a light that has no attenuation at all. The intensity, represented by the brigtness setting of the light entity, will be totally unaffected by distance, continuing until it hits a surface, theoretically capable of illuminating an infinite area. This type of light can be seen from the sky (sunlight, monlight and starlight), and other large and distant light sources.
As a 100% constant lightsource is an extreme type of light, constant light is mostly used in combination with the other two types of attenuations, to "soften" or limit them.
Linear Attenuation
This is the same light entity, but at a 0:1:0 ratio, making its lighting 100% linear instead.
Mathematically, the decline of this type of light is linear, inversely proportial to the distance from the light source (I = 1/d where I is intensity and d is distance). This means that the light intensity (set by its brightness) will diminish (at a fixed rate) as it travels from its source. To compensate for this decline, Valve has boosted the intensity of the lightsource to 100 times its brightness.
In the real world a 100% linear lightsource would be practically impossible, as it would represent a real world soft light of infinite size, but in the virtual world, a 0:1:0 lightsource is believable for most entity based lightsources.
Quadratic Attenuation
This is a normal, unmodified light source, preset to 0:0:1, making it 100% Quadratic.
Mathematically, the attenuation of a 100% quadratic light is exponential (quadratic), expressed as "I = 1/d^2", meaning that the further the light travels from its source, the more it will be diminished. This creates a very sharp drop in light. To compensate for the fast decline of quadratic lights, Valve has boosted the intensity of them to be 100^2 (10 000) times more intense than the actual intensity.
An unmodified (100% quadratic) lightsource represents a pure "point light source" in the real world. In the virtual world, this effect looks like a lightsource shining through murky water, looking far from typical real world lightsource behavior.
When used in moderation, quadratic attenuation can be used not only for small lightsources, but also to reflect light travelling through something more dispersing than air, like air humidity (like fog) or water.
Mixing Attenuation
When blending between these three types of attenuation, you set the proportions of each attenuation type against the other two types. To avoid confusion, keep in mind that you can set the scale of these proportions as you wish: A proportion of 3:6:1 gives the exact same result as 6:12:2, or 30:60:10, which can easily be translated to 30%, 60% and 10%.