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<> The Description of Material <>

It seems that a difference of illumination model of surfaces on objects is not so significant comparison with the difference of textures on them. Therefore, you have to understand illumination model for good use of them.

<> Fundamental of Material information

Our L2 system can deal only a few kind of illumination model. L2 can not express the surface like a fur nor like flow of water. What kind material model we can handle in L2? There are only 4 kinds of illumination model we can handle as follows.

most specular "Shine"
a little specular "Smooth"
a little diffuse "Normal"
most diffuse "Rough"

When you set object surfaces as "most smooth," the object reflects light strongly with sharp and focused highlight. In the opposite side, when you set object surfaces as "roughly", they will be vaguely reflection without focused highlight. Moreover, "most smooth" and "smooth" can reflect with other objects. Of course, when you set an surface "most smooth," you can get more strongly reflection effect than the case of "smooth".

<> Translucently attribute

L2 can handle some kinds of attributes of the illumination model for surfaces. First, we will introduce the translucently attribute.

When you set translucently attribute on an surface, you can see other objects through the translucently surface. In fact, there must be refractive phenomena on a translucently surface, but L2 can not simulate such a refractive effect. Only you can see other objects at the opposite side of translucently surfaces. However, even this simplified translucent algorithm has large computational effort. So, when you use many translucently surfaces in a scene, the rendering time will be huge. (The rendering time will be increase proportional to the occupation area of translucently objects increases on a screen.) Please notice it!

We call an illumination model including translucently effect as "glass" and "frosted glass." "Glass" has higher translucently effect than the "frosted glass" one. "Frosted glass" looks like roughly surface and has lower translucently effect.

We can think the combination of high translucently effect with roughly surface, or low translucently effect with smooth surface. However, an object with roughly surfaces reflect diffusely and high translucently has physically inconsistency. Thus, such combinations are eliminated in our L2. Hum, but an object can be easily imagine high translucently with smooth surfaces, mmm.

<> Luminous attribute

Second attribute with illumination model is the luminous attribute. An object with luminous attribute is not same as a luminous object. That mean an object with luminous attribute can not be a light source. The object with luminous attribute has no effect for other objects' brightness.

In the case of normal object, the brightness may be varied according to the light source position. When a light source is in front of an object surface, the surface will be bright by the light source. In other case, the surface will be darker than that case. Brightness of an object with luminous attribute has no relationship with light source position. Thus, all surfaces of an object have same brightness. Therefore, the object has no shadow and lacks of stereoscopic effect. Moreover, even if an environment has no light source, an object with luminant attribute lightens itself. This is the reason why we call this attribute as luminous attribute.

Since this luminous attribute kills the shading effect, it is no mean to say such a surface is smooth or not. However, we can think an object has an attribute as luminous and translucently. We call such attribute as "shadow attribute."

The effect of "luminous attribute" can use to express for the luminous object like a tail light of an motorcycle or hot lava. Especially, the "shadow attribute" can express shadow of other objects, since objects with shadow attribute has no stereoscopic effect and other objects under the shadow objects can be seen through the shadow objects. After all, this "luminous attribute" including shadow attribute is considered as using for special effect.

<> Colored metal attribute

The last attribute is "colored metal attribute." This attribute is almost same as "most smooth" and may not be used so much.

Colored metal means like a metal of gold, copper or etc.. This attribute express a special feature of color of metals. In the case of normal object, reflecting color will be white with light source of white color on an object, even if the object has red or blue color. Because object reflects color of a light source. However, an object with "colored metal attribute" reflects color of object. An gold object with color metal attribute glitters with gold color.

In the end, when you make an object attribute "colored metal," you can see the object with colored highlight. That's all. Please recall it when you want to render gold bars or copper boards.

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