学步园

 在OpenGL中，这里要用到很多的纹理图，但是一般我们用的都只是一些小小的控件，所以图形一般都不是很大，一般的做法就是为每一个这样的

下图都去建立一个纹理，但是这个是很没有效率的。因为opengl对于纹理的处理是先把它放在硬件上面，处理完了然后把下一个纹理放上来，这样

如果问你过多就会产生很多没有必要的纹理替换的操作，所以很有必要把很多小图贴在一个大图形上面，这样我们只用管理一张大图就OK了，一般我们的纹理图的大小是有限制的，在G1上面，好像这个限制是1024*1024.所以很多很小的图标我们都可以放在一张大图上面。

在3D纹理贴图中，这里有一个这样的概念Texture Atlas，

纹理组合

在游戏或者可视化应用中，我们总是会遇到许多非常小的纹理，一种比较好的办法是我们把这些纹理组合成一个比较大的纹理，例
如256x256，这样驱动程序在加载纹理的video
memory的地址时候，驱动程序仅仅需要加载一次家可以了。这种方法在多个造型软件中也经常见到，例如人体造型软件Pose，它将一个人的头发，脸，眼
睛，等组合为一个纹理。

建议

: 将多个小纹理组合为一个大纹理，然后修改对应三角形定点的纹理坐标，或者使用glMatrixMode(GL_TEXTURE)对定点的纹理坐标作几何变换。

这里有一个效率不是很高的算法，来做这个事情：

public class Texture {<br /> public boolean inserted;<br /> public int atlasX;<br /> public int atlasY;</p> <p> private Bitmap _bmp;<br /> private int _width;<br /> private int _height;<br /> private int _tileCols;<br /> private int _tileRows;</p> <p> public Texture(Bitmap bmp) {<br /> _bmp = bmp;<br /> _width = bmp.getWidth();<br /> _height = bmp.getHeight();<br /> _tileCols = 1;<br /> _tileRows = 1;<br /> inserted = false;<br /> }</p> <p> public Bitmap getBitmap() {<br /> return _bmp;<br /> }</p> <p> public void cleanBitmap() {<br /> _bmp.recycle();<br /> }</p> <p> public int getWidth() {<br /> return _width;<br /> }</p> <p> public int getHeight() {<br /> return _height;<br /> }</p> <p> public void setTileSize(int tileWidth, int tileHeight) {<br /> _tileCols = _width / tileWidth;<br /> _tileRows = _height / tileHeight;<br /> }</p> <p> public void setTileCount(int columns, int rows) {<br /> _tileCols = columns;<br /> _tileRows = rows;<br /> }</p> <p> public int getTileCols() {<br /> return _tileCols;<br /> }</p> <p> public int getTileRows() {<br /> return _tileRows;<br /> }<br /> }

然后就是我们纹理合并的一个类

public class TextureAtlas {<br /> public int id;<br /> public boolean ready;<br /> public boolean readyToLoad;</p> <p> private HashMap<Integer, Texture> _texture;<br /> private int _textureCount;<br /> private Bitmap _bmp;</p> <p> private int _greatestWidth; //存放的是最大的一幅图的宽</p> <p> private int _width;<br /> private int _height;</p> <p> public TextureAtlas() {<br /> _texture = new HashMap<Integer, Texture>();<br /> _textureCount = 0;<br /> readyToLoad = false;<br /> ready = false;<br /> }</p> <p> /**<br /> * @return the width of the texture atlas<br /> */<br /> public int getWidth() {<br /> return _width;<br /> }</p> <p> /**<br /> * @return the height of the texture atlas<br /> */<br /> public int getHeight() {<br /> return _height;<br /> }</p> <p> /**<br /> * Creates a Texture and puts it onto the atlas<br /> * @param resourceId reference to a drawable resource file, as described in R.java<br /> * @return NULL if failed<br /> */<br /> public Texture createTextureFromResource(int resourceId) {<br /> Bitmap bmp = BitmapFactory.decodeResource(Rokon.getRokon().getActivity().getResources(), resourceId);<br /> return createTextureFromBitmap(bmp);<br /> }</p> <p> /**<br /> * Creates a Texture and puts it onto the atlas<br /> * @param bmp a Bitmap object to build the texture from<br /> * @return NLUL if failed<br /> */<br /> public Texture createTextureFromBitmap(Bitmap bmp) {<br /> Texture texture = new Texture(bmp);<br /> if(bmp.getWidth() > _greatestWidth)<br /> _greatestWidth = bmp.getWidth();<br /> _texture.put(_textureCount, texture);<br /> Debug.print("Added " + bmp.getWidth() + "x" + bmp.getHeight() + " " + _textureCount);<br /> _textureCount++;<br /> return texture;<br /> }</p> <p> /**<br /> * Adds a Texture to the atlas, note: this is done automatically if createTextureXXX functions are used<br /> * @param texture<br /> */<br /> public void addTexture(Texture texture) {<br /> _texture.put(_textureCount, texture);<br /> _textureCount++;<br /> }</p> <p> /**<br /> * Calculates a TextureAtlas from all the loaded Texture's<br /> */<br /> public void compute() {<br /> compute(0);<br /> }</p> <p> /**<br /> * Calculates a TextureAtlas from all the loaded Texture's<br /> * The Texture's are sorted into largest-first order, and a bin packing algorithm is used to squeeze<br /> * into the atlas. There is a maximum total atlas size of 1024x1024 pixels, imposed by OpenGL.<br /> * If your Texture's and Font's do not fit into this space, an exception will be raised.<br /> *<br /> * An improvement - to allow more atlases simulatenously, is being worked on.<br /> * @param initwidth the minimum width of the atlas<br /> */<br /> public void compute(int initwidth) {<br /> _height = 0;<br /> long now = Rokon.getTime();<br /> int i = 0;<br /> _width = initwidth;<br /> if(_width == 0)<br /> while(_width < _greatestWidth)<br /> _width = (int)Math.pow(2, i++);<br /> for(i = 0; i < _textureCount; i++)<br /> _texture.get(i).inserted = false;<br /> //Debug.print("Fitting textures into max width of " + _width + " pixels");<br /> //这个插入的算法实在是不怎么样，但是比较好懂，我们按照从大到小的顺序找到所有纹理图，这个大小是按照面积的大小<br /> //对于每一当前没有插入的找到的最大的纹理，我们要做下面的处理：<br /> //</p> <p> //为这张图找一个地方插入，插入的逻辑很简单，每次x+=16然后把新的x y坐标放入，看是不是很现有的重合，如果重合<br /> //x再次+16，然后再看，当x的值都加到了边界的时候，这个时候，我们让x从左边再次开始，并且让Y值加上16<br /> for(i = 0; i < _textureCount; i++) {<br /> int greatestArea = 0;<br /> int greatestIndex = -1;<br /> for(int j = 0; j < _textureCount; j++) {<br /> if(!_texture.get(j).inserted && _texture.get(j).getWidth() * _texture.get(j).getHeight() > greatestArea) {<br /> greatestIndex = j;<br /> greatestArea = _texture.get(j).getWidth() * _texture.get(j).getHeight();<br /> }<br /> }<br /> if(greatestIndex != -1) {<br /> Texture texture = _texture.get(greatestIndex);<br /> int x = 0;<br /> int y = 0;<br /> boolean found = false;<br /> while(!found) {<br /> if(!isAnyoneWithin(x, y, x + texture.getWidth(), y + texture.getHeight())) {<br /> texture.atlasX = x;<br /> texture.atlasY = y;<br /> found = true;<br /> if(texture.atlasY + texture.getHeight() > _height)<br /> _height = texture.atlasY + texture.getHeight();<br /> } else {<br /> x += 16;<br /> if(x + texture.getWidth() > _width) {<br /> x = 0;<br /> y += 16;<br /> }<br /> }<br /> }<br /> _texture.get(greatestIndex).inserted = true;<br /> } else<br /> break;<br /> }<br /> //当把所有的图插入完毕的时候，我们替我们的高度也找一个刚好的2的N次方<br /> int theight = _height;<br /> _height = 0;<br /> i = 0;<br /> while(_height < theight)<br /> _height = (int)Math.pow(2, i++);<br /> if(_height > 1024) {<br /> //Debug.print("CANNOT PRODUCE A TEXTURE ATLAS GREATER THAN 1024x1024");<br /> if(_width < 64) {<br /> //Debug.print("CANNOT PRODUCE A TEXTURE ATLAS GREATER THAN 1024px HIGH - RETRYING WITH MORE WIDTH");<br /> compute(64);<br /> return;<br /> } else if(_width < 128) {<br /> //Debug.print("CANNOT PRODUCE A TEXTURE ATLAS GREATER THAN 1024px HIGH - RETRYING WITH MORE WIDTH");<br /> compute(128);<br /> return;<br /> } else if(_width < 256) {<br /> //Debug.print("CANNOT PRODUCE A TEXTURE ATLAS GREATER THAN 1024px HIGH - RETRYING WITH MORE WIDTH");<br /> compute(256);<br /> return;<br /> } else if(_width < 512) {<br /> //Debug.print("CANNOT PRODUCE A TEXTURE ATLAS GREATER THAN 1024px HIGH - RETRYING WITH MORE WIDTH");<br /> compute(512);<br /> return;<br /> } else if(_width < 1024) {<br /> //Debug.print("CANNOT PRODUCE A TEXTURE ATLAS GREATER THAN 1024px HIGH - RETRYING WITH MORE WIDTH");<br /> compute(1024);<br /> return;<br /> } else {<br /> Debug.print("TRY AGAIN WITH FEWER TEXTURES - OR SPREAD TO ANOTHER ATLAS");<br /> System.exit(0);<br /> return;<br /> }<br /> }<br /> _bmp = Bitmap.createBitmap(_width, _height, Bitmap.Config.ARGB_8888);<br /> Canvas canvas = new Canvas(_bmp);<br /> for(Texture texture : _texture.values()) {<br /> canvas.drawBitmap(texture.getBitmap(), texture.atlasX, texture.atlasY, new Paint());<br /> texture.cleanBitmap();<br /> }<br /> readyToLoad = true;<br /> System.gc();<br /> }</p> <p> public Bitmap getBitmap() {<br /> return _bmp;<br /> }</p> <p> public void cleanBitmap() {<br /> _bmp.recycle();<br /> }</p> <p> private boolean isAnyoneWithin(int x, int y, int x2, int y2) {<br /> for(Texture texture : _texture.values()) {<br /> if(texture.inserted) {<br /> boolean maybe = false;</p> <p> if(texture.atlasX >= x && texture.atlasX <= x2)<br /> maybe = true;</p> <p> if(texture.atlasX <= x && texture.atlasX + texture.getWidth() > x)<br /> maybe = true;</p> <p> if(maybe) {<br /> if(texture.atlasY >= y && texture.atlasY <= y2)<br /> return true;<br /> if(texture.atlasY <= y && texture.atlasY + texture.getHeight() > y)<br /> return true;<br /> }<br /> }<br /> }<br /> return false;<br /> }<br /> }<br />