# 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].

## Depth Packing

`THREE.BasicDepthPacking THREE.RGBADepthPacking`

For use with the [page:MeshDepthMaterial.depthPacking depthPacking] property of `MeshDepthMaterial`.

## Color Space

`THREE.NoColorSpace = "" THREE.SRGBColorSpace = "srgb" THREE.LinearSRGBColorSpace = "srgb-linear"`

Used to define the color space of textures (and the output color space of the renderer).
If the color space type is changed after the texture has already been used by a material, you will need to set [page:Material.needsUpdate Material.needsUpdate] to `true` to make the material recompile.

## 源代码

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