Utility Shaders - Normal Map
General概述
Normal mapping is a texture-based technique used to give the impression of sub-polygon lighting detail, without having to model it. It is controlled by a 『normal』 texture, which is used to perturb the surface normal. Since only normals are perturbed, not geometry, it does not affect shadows.
法线贴图是一个基于纹理贴图的技术，无需建模就能展示子多边形的光线细节。通过法线纹理扰乱表面的法线来控制法线贴图，因只是法线被扰乱，而不是真产生几何体，所以阴影不受影响。
The resolution of the normal map texture is important – you ideally want a one pixel per texel maximum resolution to get the best visual results. Magnifying the texture will blur the results and minifying will lessen the effect with distance.
The output of this shader is a perturbed normal.
法线贴图纹理的解析度是很重要的-------理想的情况下纹理的解析度要满足最大特写时，一个渲染像素占一个纹理像素，这样才能获得最好的效果。纹理被放大时会产生模糊，相反被缩小或者放在远处时就不会有大问题。
Shader Options著色器选项
General概述
This controls the basic properties of the normal map.
选项控制法线贴图基本属性
Texture纹理
Map贴图
This is the texture map that contains the normals.
法线的纹理贴图
Texture Space纹理空间
This is the texture mapping space, which defines the uv channel.
定义了UV通道的纹理贴图空间。
Unbiased Normals无偏法线
8-bit integer texture maps normally store values between 0.0 and 1.0, but normals
have component values between -1.0 and 1.0. When this is the case, the normals will have been pre-biased to fit into the 0.0 to 1.0 range. Check this option only when you know that the texture map is unbiased, meaning the normals were floating point and stored in the -1.0 to 1.0 range.8位整数的纹理映射通常存储在0.0和1.0之间，但法线分量值在-1.0和1.0之间。在这种情况下，法线将被预先偏移到0.0到1.0的范围内。只有在已知纹理贴图是无偏模式下时才需要勾选。也就是说，法线是以浮点数存储在-1.0到1.0之间的。
Flip Normal Y翻转Y轴
This allows you to flip the y of the normal map, which is useful if the normal map
was generated using a flipped uv coordinate system.允许你沿Y轴翻转法线贴图，如果法线贴图是使用的UV坐标系统被翻转过，那么可以使用这个选项。
Scale Normal缩放法线
This allows you to scale the resultant normal from the normal map, yielding a stronger 『bump』 effect.
允许缩放法线贴图中的合成法线偏移量，产生更强的凹凸效应。
Tangents切线
Tangents切线
This is the channel for the pre-computed surface tangents, since normal mapping is always calculated in tangent space.
预计算表面节线的通道。因为法线贴图是以切线空间计算的。
Advanced高级
This gives you extra options for filtering and defined the texture coordinates. For examples, see 『Image Sampler』 document.
提供过滤和定义纹理坐标的额外选项。有关实例，请参见Image Sampler文档。
Elliptical Filtering椭圆形过滤
Enable开启
This enables elliptical filtering, which yields the best quality for texture sampling at shallow angles. When this is not checked, bi-linear filtering will be used.
启用椭圆形过滤可在浅角度得到最好质量的纹理采样。不勾选这个选项时，将使用双线生过滤。
Maximum Eccentricity最大偏心率
This specifies the maximum eccentricity for elliptical filtering. The higher the value the better the results, but at the cost of performance. A value of 1.0 is the same as bi-linear filtering.
指定椭圆形过滤的最大离心率。数值越大效果越好，但是以性能作为代价。A数值为1.0的时等同于使用双线性过滤。
Alternate可选
U / V
This specifies whether alternate texture coordinate repetition should be reversed.
确定是否应该反转UV纹理坐标。
Repeats重复
Texture Repeats纹理重复
This controls the repetition of the texture coordinates. Normally a texture is mapped with values 0.0 to 1.0, to cover the whole texture. A 『Texture Repeat』 value of 2.0, for example, means that the whole texture will fit twice in the same 0.0 to 1.0 range. Values lower than 1.0 effectively act as magnification.
控制纹理坐标的重复。通常要覆盖整个纹理， 一个纹理映射值在0.0到1.0之间。比如Texture
Repeat的值为2.0时，意味著整个纹理在0.0到1.0之间重复2次。数值小于1.0会放大纹理。Wrap U/V包裹
This enables U/V wrapping when the values are out of the 0.0 – 1.0 range.
数值不在0.0到1.0范围内时，启动UV包裹。
This option is only available in Maya. Softimage does not need this.
这个选项仅Maya 可用，Softimage不需要。
UV Remap UV冲贴图
Minimum / Maximum最小/最大
This specifies the range in which the texture coordinates will be remapped to.
指定纹理坐标重新映射的范围。
Normal Map Example
Here is an example of how a normal map can enhance the lighting detail of simple, flat geometry.
此处举例说明一个Normal Map如何能提高简单的平面几何的灯光细节。
The following simple example shows an un-textured surface, with a diffuse and glossy reflected spherical area light.以下是个简单的例子，物体表面没有纹理贴图，区域光源对Diffuse和Glossy Reflected起作用。
The example below noew shows how a normal map can dramatically increase the lighting detail, without paying for the extra polygons.下面的例子显示了法线贴图如何显著地提高灯光细节，且无须为这些多出的细节付出任何渲染成本。
The image below shows the normal map that was used to create the effect.下图显示了用来达成效果的法线贴图。
推荐阅读：
