# 纹理常量（Texture Constants）

## 映射模式

`THREE.UVMapping THREE.CubeReflectionMapping THREE.CubeRefractionMapping THREE.EquirectangularReflectionMapping THREE.EquirectangularRefractionMapping THREE.CubeUVReflectionMapping`

这些常量定义了纹理贴图的映射模式。
[page:Constant UVMapping]是默认值，纹理使用网格的坐标来进行映射。
其它的值定义了环境映射的类型。
[page:Constant CubeReflectionMapping] 和 [page:Constant CubeRefractionMapping] 用于 [page:CubeTexture CubeTexture] —— 由6个纹理组合而成，每个纹理都是立方体的一个面。 对于[page:CubeTexture CubeTexture]来说，[page:Constant CubeReflectionMapping]是其默认值。
[page:Constant EquirectangularReflectionMapping] 和 [page:Constant EquirectangularRefractionMapping] 用于等距圆柱投影的环境贴图，也被叫做经纬线映射贴图。等距圆柱投影贴图表示沿着其水平中线360°的视角，以及沿着其垂直轴向180°的视角。贴图顶部和底部的边缘分别对应于它所映射的球体的北极和南极。
请查看示例：[example:webgl_materials_envmaps materials / envmaps] 。

## 包裹模式

`THREE.RepeatWrapping THREE.ClampToEdgeWrapping THREE.MirroredRepeatWrapping`

这些常量定义了纹理贴图的 [page:Texture.wrapS wrapS] 和 [page:Texture.wrapT wrapT] 属性，定义了水平和垂直方向上纹理的包裹方式。
使用[page:constant RepeatWrapping]，纹理将简单地重复到无穷大。 With [page:constant RepeatWrapping] the texture will simply repeat to infinity.
[page:constant ClampToEdgeWrapping]是默认值，纹理中的最后一个像素将延伸到网格的边缘。
使用[page:constant MirroredRepeatWrapping]， 纹理将重复到无穷大，在每次重复时将进行镜像。

## 放大滤镜（Magnification Filters）

`THREE.NearestFilter THREE.LinearFilter`

这些常量用于纹理的[page:Texture.magFilter magFilter]属性，它们定义了当被纹理化的像素映射到小于或者等于1纹理元素（texel）的区域时，将要使用的纹理放大函数。
[page:constant NearestFilter]返回与指定纹理坐标（在曼哈顿距离之内）最接近的纹理元素的值。
[page:constant LinearFilter]是默认值，返回距离指定的纹理坐标最近的四个纹理元素的加权平均值， 并且可以包含纹理的其他部分中，被包裹或者被重复的项目，具体取决于 [page:Texture.wrapS wrapS] 和 [page:Texture.wrapT wrapT] 的值，and on the exact mapping。

## 缩小滤镜（Minification Filters）

`THREE.NearestFilter THREE.NearestMipmapNearestFilter THREE.NearestMipmapLinearFilter THREE.LinearFilter THREE.LinearMipmapNearestFilter THREE.LinearMipmapLinearFilter`

这些常量用于纹理的[page:Texture.minFilter minFilter]属性，它们定义了当被纹理化的像素映射到大于1纹理元素（texel）的区域时，将要使用的纹理缩小函数。
除了[page:constant NearestFilter] 和 [page:constant LinearFilter]， 下面的四个函数也可以用于缩小：
[page:constant NearestMipmapNearestFilter]选择与被纹理化像素的尺寸最匹配的mipmap， 并以[page:constant NearestFilter]（最靠近像素中心的纹理元素）为标准来生成纹理值。
[page:constant NearestMipmapLinearFilter]选择与被纹理化像素的尺寸最接近的两个mipmap， 并以[page:constant NearestFilter]为标准来从每个mipmap中生成纹理值。最终的纹理值是这两个值的加权平均值。
[page:constant LinearMipmapNearestFilter]选择与被纹理化像素的尺寸最匹配的mipmap， 并以[page:constant LinearFilter]（最靠近像素中心的四个纹理元素的加权平均值）为标准来生成纹理值。
[page:constant LinearMipmapLinearFilter]是默认值，它选择与被纹理化像素的尺寸最接近的两个mipmap， 并以[page:constant LinearFilter]为标准来从每个mipmap中生成纹理值。最终的纹理值是这两个值的加权平均值。
请查看示例：[example:webgl_materials_texture_filters materials / texture / filters]。

## 类型

`THREE.UnsignedByteType THREE.ByteType THREE.ShortType THREE.UnsignedShortType THREE.IntType THREE.UnsignedIntType THREE.FloatType THREE.HalfFloatType THREE.UnsignedShort4444Type THREE.UnsignedShort5551Type THREE.UnsignedInt248Type`

这些常量用于纹理的[page:Texture.type type]属性，这些属性必须与正确的格式相对应。详情请查看下方。
[page:constant UnsignedByteType] 是默认值。

## 格式

`THREE.AlphaFormat THREE.RedFormat THREE.RedIntegerFormat THREE.RGFormat THREE.RGIntegerFormat THREE.RGBAFormat THREE.RGBAIntegerFormat THREE.LuminanceFormat THREE.LuminanceAlphaFormat THREE.DepthFormat THREE.DepthStencilFormat`

这些常量用于纹理的[page:Texture.format format]属性，它们定义了shader（着色器）将如何读取的2D纹理或者*texels*（纹理元素）的元素。.
[page:constant AlphaFormat] 丢弃红、绿、蓝分量，仅读取Alpha分量。
[page:constant RedFormat] discards the green and blue components and reads just the red component.
[page:constant RedIntegerFormat] discards the green and blue components and reads just the red component. The texels are read as integers instead of floating point. (can only be used with a WebGL 2 rendering context).
[page:constant RGFormat] discards the alpha, and blue components and reads the red, and green components. (can only be used with a WebGL 2 rendering context).
[page:constant RGIntegerFormat] discards the alpha, and blue components and reads the red, and green components. The texels are read as integers instead of floating point. (can only be used with a WebGL 2 rendering context).
[page:constant RGBAFormat] 是默认值，它将读取红、绿、蓝和Alpha分量。
[page:constant RGBAIntegerFormat] is the default and reads the red, green, blue and alpha components. The texels are read as integers instead of floating point. (can only be used with a WebGL 2 rendering context).
[page:constant LuminanceFormat] 将每个元素作为单独的亮度分量来读取。 将其转换为范围限制在[0,1]区间的浮点数，然后通过将亮度值放入红、绿、蓝通道，并将1.0赋给Alpha通道，来组装成一个RGBA元素。
[page:constant LuminanceAlphaFormat] 将每个元素同时作为亮度分量和Alpha分量来读取。 和上面[page:constant LuminanceFormat]的处理过程是一致的，除了Alpha分量具有除了*1.0*以外的值。
[page:constant DepthFormat]将每个元素作为单独的深度值来读取，将其转换为范围限制在[0,1]区间的浮点数。 它是[page:DepthTexture DepthTexture]的默认值。
[page:constant DepthStencilFormat]将每个元素同时作为一对深度值和模板值来读取。 其中的深度分量解释为[page:constant DepthFormat]。 模板分量基于深度+模板的内部格式来进行解释。
请注意，纹理必须具有正确的[page:Texture.type type]设置，正如上一节所描述的那样。 请参阅[link:https://developer.mozilla.org/en/docs/Web/API/WebGLRenderingContext/texImage2D WebGLRenderingContext.texImage2D] 来获得有关详细信息。

## DDS / ST3C 压缩纹理格式

`THREE.RGB_S3TC_DXT1_Format THREE.RGBA_S3TC_DXT1_Format THREE.RGBA_S3TC_DXT3_Format THREE.RGBA_S3TC_DXT5_Format`

要使用[page:CompressedTexture CompressedTexture]中的[page:Texture.format format]属性， 需要获得[link:https://www.khronos.org/registry/webgl/extensions/WEBGL_compressed_texture_s3tc/ WEBGL_compressed_texture_s3tc] 扩展的支持。
通过这个扩展，这里的四种[link:https://en.wikipedia.org/wiki/S3_Texture_Compression S3TC]格式将可以使用：
[page:constant RGB_S3TC_DXT1_Format]：RGB图像格式的DXT1压缩图像。 [page:constant RGBA_S3TC_DXT1_Format]：RGB图像格式的DXT1压缩图像，Alpha仅具有是/否透明两个值。
[page:constant RGBA_S3TC_DXT3_Format]：RGBA图像格式的DXT3压缩图像，和32位RGBA纹理贴图相比，它提供了4:1的压缩比。
[page:constant RGBA_S3TC_DXT5_Format]：RGBA图像格式的DXT5压缩图像，它也提供了4:1的压缩比，但与DX3格式的不同之处在于其Alpha是如何被压缩的。

## PVRTC 压缩纹理格式（PVRTC Compressed Texture Formats）

`THREE.RGB_PVRTC_4BPPV1_Format THREE.RGB_PVRTC_2BPPV1_Format THREE.RGBA_PVRTC_4BPPV1_Format THREE.RGBA_PVRTC_2BPPV1_Format`

要使用[page:CompressedTexture CompressedTexture]中的[page:Texture.format format]属性，需要获得 [link:https://www.khronos.org/registry/webgl/extensions/WEBGL_compressed_texture_pvrtc/ WEBGL_compressed_texture_pvrtc] 扩展的支持。
PVRTC通常只在具有PowerVR芯片的移动设备上可用，这些设备主要是苹果设备。
通过这个扩展，这里的四种[link:https://en.wikipedia.org/wiki/PVRTC PVRTC]格式将可以使用：
[page:constant RGB_PVRTC_4BPPV1_Format]：4位模式下的RGB压缩，每4x4像素一个块。
[page:constant RGB_PVRTC_2BPPV1_Format]：2位模式下的RGB压缩，每8x4像素一个块。
[page:constant RGBA_PVRTC_4BPPV1_Format]: 4位模式下的RGBA压缩，每4x4像素一个块。
[page:constant RGBA_PVRTC_2BPPV1_Format]: 2位模式下的RGB压缩，每8x4像素一个块。

## ETC 压缩纹理格式

`THREE.RGB_ETC1_Format THREE.RGB_ETC2_Format THREE.RGBA_ETC2_EAC_Format`

For use with a [page:CompressedTexture CompressedTexture]'s [page:Texture.format format] property, these require support for the [link:https://www.khronos.org/registry/webgl/extensions/WEBGL_compressed_texture_etc1/ WEBGL_compressed_texture_etc1] (ETC1) or [link:https://www.khronos.org/registry/webgl/extensions/WEBGL_compressed_texture_etc/ WEBGL_compressed_texture_etc] (ETC2) extensions.

## ASTC Compressed Texture Format

`THREE.RGBA_ASTC_4x4_Format THREE.RGBA_ASTC_5x4_Format THREE.RGBA_ASTC_5x5_Format THREE.RGBA_ASTC_6x5_Format THREE.RGBA_ASTC_6x6_Format THREE.RGBA_ASTC_8x5_Format THREE.RGBA_ASTC_8x6_Format THREE.RGBA_ASTC_8x8_Format THREE.RGBA_ASTC_10x5_Format THREE.RGBA_ASTC_10x6_Format THREE.RGBA_ASTC_10x8_Format THREE.RGBA_ASTC_10x10_Format THREE.RGBA_ASTC_12x10_Format THREE.RGBA_ASTC_12x12_Format`

For use with a [page:CompressedTexture CompressedTexture]'s [page:Texture.format format] property, these require support for the [link:https://www.khronos.org/registry/webgl/extensions/WEBGL_compressed_texture_astc/ WEBGL_compressed_texture_astc] extension.

## Internal Formats

`'ALPHA' 'RGB' 'RGBA' 'LUMINANCE' 'LUMINANCE_ALPHA' 'RED_INTEGER' 'R8' 'R8_SNORM' 'R8I' 'R8UI' 'R16I' 'R16UI' 'R16F' 'R32I' 'R32UI' 'R32F' 'RG8' 'RG8_SNORM' 'RG8I' 'RG8UI' 'RG16I' 'RG16UI' 'RG16F' 'RG32I' 'RG32UI' 'RG32F' 'RGB565' 'RGB8' 'RGB8_SNORM' 'RGB8I' 'RGB8UI' 'RGB16I' 'RGB16UI' 'RGB16F' 'RGB32I' 'RGB32UI' 'RGB32F' 'RGB9_E5' 'SRGB8' 'R11F_G11F_B10F' 'RGBA4' 'RGBA8' 'RGBA8_SNORM' 'RGBA8I' 'RGBA8UI' 'RGBA16I' 'RGBA16UI' 'RGBA16F' 'RGBA32I' 'RGBA32UI' 'RGBA32F' 'RGB5_A1' 'RGB10_A2' 'RGB10_A2UI' 'SRGB8_ALPHA8' 'DEPTH_COMPONENT16' 'DEPTH_COMPONENT24' 'DEPTH_COMPONENT32F' 'DEPTH24_STENCIL8' 'DEPTH32F_STENCIL8'`

Heads up: changing the internal format of a texture will only affect the texture when using a WebGL 2 rendering context.
For use with a texture's [page:Texture.internalFormat internalFormat] property, these define how elements of a texture, or *texels*, are stored on the GPU.
[page:constant R8] stores the red component on 8 bits.
[page:constant R8_SNORM] stores the red component on 8 bits. The component is stored as normalized.
[page:constant R8I] stores the red component on 8 bits. The component is stored as an integer.
[page:constant R8UI] stores the red component on 8 bits. The component is stored as an unsigned integer.
[page:constant R16I] stores the red component on 16 bits. The component is stored as an integer.
[page:constant R16UI] stores the red component on 16 bits. The component is stored as an unsigned integer.
[page:constant R16F] stores the red component on 16 bits. The component is stored as floating point.
[page:constant R32I] stores the red component on 32 bits. The component is stored as an integer.
[page:constant R32UI] stores the red component on 32 bits. The component is stored as an unsigned integer.
[page:constant R32F] stores the red component on 32 bits. The component is stored as floating point.
[page:constant RG8] stores the red and green components on 8 bits each.
[page:constant RG8_SNORM] stores the red and green components on 8 bits each. Every component is stored as normalized.
[page:constant RG8I] stores the red and green components on 8 bits each. Every component is stored as an integer.
[page:constant RG8UI] stores the red and green components on 8 bits each. Every component is stored as an unsigned integer.
[page:constant RG16I] stores the red and green components on 16 bits each. Every component is stored as an integer.
[page:constant RG16UI] stores the red and green components on 16 bits each. Every component is stored as an unsigned integer.
[page:constant RG16F] stores the red and green components on 16 bits each. Every component is stored as floating point.
[page:constant RG32I] stores the red and green components on 32 bits each. Every component is stored as an integer.
[page:constant RG32UI] stores the red and green components on 32 bits. Every component is stored as an unsigned integer.
[page:constant RG32F] stores the red and green components on 32 bits. Every component is stored as floating point.
[page:constant RGB8] stores the red, green, and blue components on 8 bits each. [page:constant RGB8_SNORM] stores the red, green, and blue components on 8 bits each. Every component is stored as normalized.
[page:constant RGB8I] stores the red, green, and blue components on 8 bits each. Every component is stored as an integer.
[page:constant RGB8UI] stores the red, green, and blue components on 8 bits each. Every component is stored as an unsigned integer.
[page:constant RGB16I] stores the red, green, and blue components on 16 bits each. Every component is stored as an integer.
[page:constant RGB16UI] stores the red, green, and blue components on 16 bits each. Every component is stored as an unsigned integer.
[page:constant RGB16F] stores the red, green, and blue components on 16 bits each. Every component is stored as floating point
[page:constant RGB32I] stores the red, green, and blue components on 32 bits each. Every component is stored as an integer.
[page:constant RGB32UI] stores the red, green, and blue components on 32 bits each. Every component is stored as an unsigned integer.
[page:constant RGB32F] stores the red, green, and blue components on 32 bits each. Every component is stored as floating point
[page:constant R11F_G11F_B10F] stores the red, green, and blue components respectively on 11 bits, 11 bits, and 10bits. Every component is stored as floating point.
[page:constant RGB565] stores the red, green, and blue components respectively on 5 bits, 6 bits, and 5 bits.
[page:constant RGB9_E5] stores the red, green, and blue components on 9 bits each.
[page:constant RGBA8] stores the red, green, blue, and alpha components on 8 bits each.
[page:constant RGBA8_SNORM] stores the red, green, blue, and alpha components on 8 bits. Every component is stored as normalized.
[page:constant RGBA8I] stores the red, green, blue, and alpha components on 8 bits each. Every component is stored as an integer.
[page:constant RGBA8UI] stores the red, green, blue, and alpha components on 8 bits. Every component is stored as an unsigned integer.
[page:constant RGBA16I] stores the red, green, blue, and alpha components on 16 bits. Every component is stored as an integer.
[page:constant RGBA16UI] stores the red, green, blue, and alpha components on 16 bits. Every component is stored as an unsigned integer.
[page:constant RGBA16F] stores the red, green, blue, and alpha components on 16 bits. Every component is stored as floating point.
[page:constant RGBA32I] stores the red, green, blue, and alpha components on 32 bits. Every component is stored as an integer.
[page:constant RGBA32UI] stores the red, green, blue, and alpha components on 32 bits. Every component is stored as an unsigned integer.
[page:constant RGBA32F] stores the red, green, blue, and alpha components on 32 bits. Every component is stored as floating point.
[page:constant RGB5_A1] stores the red, green, blue, and alpha components respectively on 5 bits, 5 bits, 5 bits, and 1 bit.
[page:constant RGB10_A2] stores the red, green, blue, and alpha components respectively on 10 bits, 10 bits, 10 bits and 2 bits.
[page:constant RGB10_A2UI] stores the red, green, blue, and alpha components respectively on 10 bits, 10 bits, 10 bits and 2 bits. Every component is stored as an unsigned integer.
[page:constant SRGB8] stores the red, green, and blue components on 8 bits each.
[page:constant SRGB8_ALPHA8] stores the red, green, blue, and alpha components on 8 bits each.
[page:constant DEPTH_COMPONENT16] stores the depth component on 16bits.
[page:constant DEPTH_COMPONENT24] stores the depth component on 24bits.
[page:constant DEPTH_COMPONENT32F] stores the depth component on 32bits. The component is stored as floating point.
[page:constant DEPTH24_STENCIL8] stores the depth, and stencil components respectively on 24 bits and 8 bits. The stencil component is stored as an unsigned integer.
[page:constant DEPTH32F_STENCIL8] stores the depth, and stencil components respectively on 32 bits and 8 bits. The depth component is stored as floating point, and the stencil component as an unsigned integer.
Note that the texture must have the correct [page:Texture.type type] set, as well as the correct [page:Texture.format format]. See [link:https://developer.mozilla.org/en/docs/Web/API/WebGLRenderingContext/texImage2D WebGLRenderingContext.texImage2D], and [link:https://developer.mozilla.org/en-US/docs/Web/API/WebGL2RenderingContext/texImage3D WebGL2RenderingContext.texImage3D], for more details regarding the possible combination of [page:Texture.format format], [page:Texture.internalFormat internalFormat], and [page:Texture.type type].
For more in-depth information regarding internal formats, you can also refer directly to the [link:https://www.khronos.org/registry/webgl/specs/latest/2.0/ WebGL2 Specification] and to the [link:https://www.khronos.org/registry/OpenGL/specs/es/3.0/es_spec_3.0.pdf OpenGL ES 3.0 Specification].

## 编码

`THREE.LinearEncoding THREE.sRGBEncoding THREE.BasicDepthPacking THREE.RGBADepthPacking`

这些常量用于纹理的[page:Texture.encoding encoding]属性。
如果编码类型在纹理已被一个材质使用之后发生了改变， 你需要来设置[page:Material.needsUpdate Material.needsUpdate]为*true*来使得材质重新编译。
[page:constant LinearEncoding]是默认值。 除此之外的其他值仅在材质的贴图、envMap和emissiveMap中有效。

## 源代码

[link:https://github.com/mrdoob/three.js/blob/master/src/constants.js src/constants.js]