starling教程-纹理（Texture）（五）

texture是被创建来填充Image对象的，Texture和Image的关系就好像是本地的BitmapData和Bitmap的关系一样。Texture类包含如下的apis：

•  base : The Stage3D texture object the texture is based on.
•  dispose : Disposes the underlying texture data.
•  empty : Returns a Texture object out of dimensions (width and height).
•  frame : The texture frame (see class description).
•  fromBitmap : Returns a Texture object out of a Bitmap object. This Bitmap object can be embedded or loaded
dynamically.
•  fromBitmapData : Returns a Texture object out of a BitmapData object.
•  fromAtfData : Allows the use of a compressed texture using the ATF (Adobe Texture Format). Compressed
textures allows you to save a lot of memory especially on constrained environments like mobile devices.
•  fromTexture : Allows the use of a texture and returns a new texture.
•  height : The height of the texture in pixels.
•  mipmapping : Indicates if the texture contains mip maps.
•  premultipliedAlpha : Indicates if the alpha values are premultiplied into the RGB values.
•  repeat : Indicates if the texture should repeat like a wallpaper or stretch the outermost pixels.
•  width : The width of the texture in pixels.

你的纹理可以使用不同的图片格式，下面是它支持的文件格式列表：

•  PNG : As alpha channel is often required, PNG is one of the most common file format used for textures.
•  JPEG : The classic JPEG format can also be used. Remember that on the GPU the image will be decompressed,
so using JPEG will not limit the memory usage and you will not be able to use transparency in your textures.
•  JPEG-XR : JPEG XR (abbr. for JPEG extended range[4]) is a still-image compression standard and file format
for continuous tone photographic images, based on technology originally developed and patented by Microsoft
under the name HD Photo (formerly Windows Media Photo). It supports both lossy and lossless compression,
and is the preferred image format for Ecma-388 Open XML Paper Specification documents.
•  ATF : Adobe Texture Format. This is the best file format for the best compression. ATF files are primarily a
file container to store lossy texture data. It achieves its lossy compression through to the use of two common
techniques: JPEG-XR1 compression and block based compression. JPEG-XR compression provide a
competitive method to save storage space and network bandwidth. Block based compression provides a way to
reduce texture memory usage on the client, at a fixed ratio of 1:8 compared to RGBA textures. ATF supports
three types of block based compression: DXT12, ETC13 and PVRTC4.

下面让我们来更深入的了解一下纹理的概念，并揭开gpu处理图片的本质-mip映射（什么是mip映射呢？看链接http://zhidao.baidu.com/question/14496010）。mip映射是一个很重要并且容易弄懂的概念。将一个texture缩小成不同的版本就是mipmap。