GLSurfaceView是OpenGL中的一个类，也是能够预览Camera的，并且在预览Camera上有其独到之处。
独到之处在哪？当使用Surfaceview无能为力、痛不欲生时就仅仅有使用GLSurfaceView了。它能够真正做到让Camera的数据和显示分离，所以搞明确了这个，像Camera仅仅开预览不显示这都是小菜，妥妥的。
Android4.0的自带Camera源代码是用SurfaceView预览的。但到了4.2就换成了GLSurfaceView来预览。
现在到了4.4又用了自家的TextureView。所以从中能够窥探出新增TextureView的用意。
虽说Android4.2的Camera源代码是用GLSurfaceView预览的，可是进行了大量的封装又封装的。由于是OpenGL小白，真是看的不知所云。
俺滴要求不高，仅仅想弄个可拍照的摸清GLSurfaceView在预览Camera上的使用流程。经过一番百度一无所获。后来翻出去Google一大圈也没发现可用的。
倒是非常多人都在用GLSurfaceView和Surfaceview同一时候预览Camera，Surfaceview用来预览数据，在上面又铺了一层GLSurfaceView绘制一些信息。无奈自己摸索，整出来的是能拍照也能得到数据。可是界面上不是一块白板就是一块黑板啥都不显示。后来在stackoverflow最终找到了一个可用的。哈哈。苍天啊。最终柳暗花明了！參考此链接，自己又改改摸索了一天才彻底搞定。之所以费这么多时间是不明确OpenGL ES2.0的绘制基本流程，跟简单的OpenGL的绘制还是稍有区别。
以下上源代码:
一、CameraGLSurfaceView.java 此类继承GLSurfaceView，并实现了两个接口
package org.yanzi.camera.preview;import javax.microedition.khronos.egl.EGLConfig;import javax.microedition.khronos.opengles.GL10;import org.yanzi.camera.CameraInterface;import android.content.Context;import android.graphics.SurfaceTexture;import android.opengl.GLES11Ext;import android.opengl.GLES20;import android.opengl.GLSurfaceView;import android.opengl.GLSurfaceView.Renderer;import android.util.AttributeSet;import android.util.Log;public class CameraGLSurfaceView extends GLSurfaceView implements Renderer, SurfaceTexture.OnFrameAvailableListener { private static final String TAG = "yanzi"; Context mContext; SurfaceTexture mSurface; int mTextureID = -1; DirectDrawer mDirectDrawer; public CameraGLSurfaceView(Context context, AttributeSet attrs) { super(context, attrs); // TODO Auto-generated constructor stub mContext = context; setEGLContextClientVersion(2); setRenderer(this); setRenderMode(RENDERMODE_WHEN_DIRTY); } @Override public void onSurfaceCreated(GL10 gl, EGLConfig config) { // TODO Auto-generated method stub Log.i(TAG, "onSurfaceCreated..."); mTextureID = createTextureID(); mSurface = new SurfaceTexture(mTextureID); mSurface.setOnFrameAvailableListener(this); mDirectDrawer = new DirectDrawer(mTextureID); CameraInterface.getInstance().doOpenCamera(null); } @Override public void onSurfaceChanged(GL10 gl, int width, int height) { // TODO Auto-generated method stub Log.i(TAG, "onSurfaceChanged..."); GLES20.glViewport(0, 0, width, height); if(!CameraInterface.getInstance().isPreviewing()){ CameraInterface.getInstance().doStartPreview(mSurface, 1.33f); } } @Override public void onDrawFrame(GL10 gl) { // TODO Auto-generated method stub Log.i(TAG, "onDrawFrame..."); GLES20.glClearColor(1.0f, 1.0f, 1.0f, 1.0f); GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT | GLES20.GL_DEPTH_BUFFER_BIT); mSurface.updateTexImage(); float[] mtx = new float[16]; mSurface.getTransformMatrix(mtx); mDirectDrawer.draw(mtx); } @Override public void onPause() { // TODO Auto-generated method stub super.onPause(); CameraInterface.getInstance().doStopCamera(); } private int createTextureID() { int[] texture = new int[1]; GLES20.glGenTextures(1, texture, 0); GLES20.glBindTexture(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, texture[0]); GLES20.glTexParameterf(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, GL10.GL_TEXTURE_MIN_FILTER,GL10.GL_LINEAR); GLES20.glTexParameterf(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, GL10.GL_TEXTURE_MAG_FILTER, GL10.GL_LINEAR); GLES20.glTexParameteri(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, GL10.GL_TEXTURE_WRAP_S, GL10.GL_CLAMP_TO_EDGE); GLES20.glTexParameteri(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, GL10.GL_TEXTURE_WRAP_T, GL10.GL_CLAMP_TO_EDGE); return texture[0]; } public SurfaceTexture _getSurfaceTexture(){ return mSurface; } @Override public void onFrameAvailable(SurfaceTexture surfaceTexture) { // TODO Auto-generated method stub Log.i(TAG, "onFrameAvailable..."); this.requestRender(); }} 关于这个类进行简单说明: 1、Renderer这个接口里有三个回调: onSurfaceCreated() onSurfaceChanged() onDrawFrame(),在onSurfaceCreated里设置了GLSurfaceView的版本号: setEGLContextClientVersion(2); 假设没这个设置是啥都画不出来了，由于Android支持OpenGL ES1.1和2.0及最新的3.0，并且版本号间区别非常大。不告诉他版本号他不知道用哪个版本号的api渲染。
在设置setRenderer(this);后，再设置它的模式为RENDERMODE_WHEN_DIRTY。这个也非常关键，看api：
When renderMode is RENDERMODE_CONTINUOUSLY, the renderer is called repeatedly to re-render the scene. When renderMode is RENDERMODE_WHEN_DIRTY, the renderer only rendered when the surface is created, or when requestRender is called. Defaults to RENDERMODE_CONTINUOUSLY.
Using RENDERMODE_WHEN_DIRTY can improve battery life and overall system performance by allowing the GPU and CPU to idle when the view does not need to be updated.
大意是RENDERMODE_CONTINUOUSLY模式就会一直Render，假设设置成RENDERMODE_WHEN_DIRTY。就是当有数据时才rendered或者主动调用了GLSurfaceView的requestRender.默认是连续模式，非常显然Camera适合脏模式，一秒30帧，当有数据来时再渲染。
2、正因是RENDERMODE_WHEN_DIRTY所以就要告诉GLSurfaceView什么时候Render，也就是啥时候进到onDrawFrame()这个函数里。SurfaceTexture.OnFrameAvailableListener这个接口就干了这么一件事，当有数据上来后会进到
public void onFrameAvailable(SurfaceTexture surfaceTexture) { // TODO Auto-generated method stub Log.i(TAG, "onFrameAvailable..."); this.requestRender(); }
这里，然后运行requestRender()。
3、网上有一些OpenGL ES的演示样例是在Activity里实现了SurfaceTexture.OnFrameAvailableListener此接口，事实上这个无所谓。
不管是被谁实现。关键看在回调里干了什么事。
4、与TextureView里对照可知，TextureView预览时由于实现了SurfaceTextureListener会自己主动创建SurfaceTexture。但在GLSurfaceView里则要手动创建同一时候绑定一个纹理ID。
5、本文在onSurfaceCreated()里打开Camera，在onSurfaceChanged()里开启预览，默认1.33的比例。
原因是相比前两种预览，此处SurfaceTexture创建须要一定时间。假设想要开预览时由Activity发起，则要GLSurfaceView利用Handler将创建的SurfaceTexture传递给Activity。
二、DirectDrawer.java 此类非常关键，负责将SurfaceTexture内容绘制到屏幕上
package org.yanzi.camera.preview;import java.nio.ByteBuffer;import java.nio.ByteOrder;import java.nio.FloatBuffer;import java.nio.ShortBuffer;import android.opengl.GLES11Ext;import android.opengl.GLES20;import android.opengl.Matrix;public class DirectDrawer { private final String vertexShaderCode = "attribute vec4 vPosition;" + "attribute vec2 inputTextureCoordinate;" + "varying vec2 textureCoordinate;" + "void main()" + "{"+ "gl_Position = vPosition;"+ "textureCoordinate = inputTextureCoordinate;" + "}"; private final String fragmentShaderCode = "#extension GL_OES_EGL_image_external : require\n"+ "precision mediump float;" + "varying vec2 textureCoordinate;\n" + "uniform samplerExternalOES s_texture;\n" + "void main() {" + " gl_FragColor = texture2D( s_texture, textureCoordinate );\n" + "}"; private FloatBuffer vertexBuffer, textureVerticesBuffer; private ShortBuffer drawListBuffer; private final int mProgram; private int mPositionHandle; private int mTextureCoordHandle; private short drawOrder[] = { 0, 1, 2, 0, 2, 3 }; // order to draw vertices // number of coordinates per vertex in this array private static final int COORDS_PER_VERTEX = 2; private final int vertexStride = COORDS_PER_VERTEX * 4; // 4 bytes per vertex static float squareCoords[] = { -1.0f, 1.0f, -1.0f, -1.0f, 1.0f, -1.0f, 1.0f, 1.0f, }; static float textureVertices[] = { 0.0f, 1.0f, 1.0f, 1.0f, 1.0f, 0.0f, 0.0f, 0.0f, }; private int texture; public DirectDrawer(int texture) { this.texture = texture; // initialize vertex byte buffer for shape coordinates ByteBuffer bb = ByteBuffer.allocateDirect(squareCoords.length * 4); bb.order(ByteOrder.nativeOrder()); vertexBuffer = bb.asFloatBuffer(); vertexBuffer.put(squareCoords); vertexBuffer.position(0); // initialize byte buffer for the draw list ByteBuffer dlb = ByteBuffer.allocateDirect(drawOrder.length * 2); dlb.order(ByteOrder.nativeOrder()); drawListBuffer = dlb.asShortBuffer(); drawListBuffer.put(drawOrder); drawListBuffer.position(0); ByteBuffer bb2 = ByteBuffer.allocateDirect(textureVertices.length * 4); bb2.order(ByteOrder.nativeOrder()); textureVerticesBuffer = bb2.asFloatBuffer(); textureVerticesBuffer.put(textureVertices); textureVerticesBuffer.position(0); int vertexShader = loadShader(GLES20.GL_VERTEX_SHADER, vertexShaderCode); int fragmentShader = loadShader(GLES20.GL_FRAGMENT_SHADER, fragmentShaderCode); mProgram = GLES20.glCreateProgram(); // create empty OpenGL ES Program GLES20.glAttachShader(mProgram, vertexShader); // add the vertex shader to program GLES20.glAttachShader(mProgram, fragmentShader); // add the fragment shader to program GLES20.glLinkProgram(mProgram); // creates OpenGL ES program executables } public void draw(float[] mtx) { GLES20.glUseProgram(mProgram); GLES20.glActiveTexture(GLES20.GL_TEXTURE0); GLES20.glBindTexture(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, texture); // get handle to vertex shader's vPosition member mPositionHandle = GLES20.glGetAttribLocation(mProgram, "vPosition"); // Enable a handle to the triangle vertices GLES20.glEnableVertexAttribArray(mPositionHandle); // Prepare the coordinate data GLES20.glVertexAttribPointer(mPositionHandle, COORDS_PER_VERTEX, GLES20.GL_FLOAT, false, vertexStride, vertexBuffer); mTextureCoordHandle = GLES20.glGetAttribLocation(mProgram, "inputTextureCoordinate"); GLES20.glEnableVertexAttribArray(mTextureCoordHandle); // textureVerticesBuffer.clear();// textureVerticesBuffer.put( transformTextureCoordinates( textureVertices, mtx ));// textureVerticesBuffer.position(0); GLES20.glVertexAttribPointer(mTextureCoordHandle, COORDS_PER_VERTEX, GLES20.GL_FLOAT, false, vertexStride, textureVerticesBuffer); GLES20.glDrawElements(GLES20.GL_TRIANGLES, drawOrder.length, GLES20.GL_UNSIGNED_SHORT, drawListBuffer); // Disable vertex array GLES20.glDisableVertexAttribArray(mPositionHandle); GLES20.glDisableVertexAttribArray(mTextureCoordHandle); } private int loadShader(int type, String shaderCode){ // create a vertex shader type (GLES20.GL_VERTEX_SHADER) // or a fragment shader type (GLES20.GL_FRAGMENT_SHADER) int shader = GLES20.glCreateShader(type); // add the source code to the shader and compile it GLES20.glShaderSource(shader, shaderCode); GLES20.glCompileShader(shader); return shader; } private float[] transformTextureCoordinates( float[] coords, float[] matrix) { float[] result = new float[ coords.length ]; float[] vt = new float[4]; for ( int i = 0 ; i < coords.length ; i += 2 ) { float[] v = { coords[i], coords[i+1], 0 , 1 }; Matrix.multiplyMV(vt, 0, matrix, 0, v, 0); result[i] = vt[0]; result[i+1] = vt[1]; } return result; }} 三、有了上面两个类就完毕95%的工作，能够将GLSurfaceView看成是有生命周期的。在onPause里进行关闭Camera。在Activity里复写两个方法: @Override protected void onResume() { // TODO Auto-generated method stub super.onResume(); glSurfaceView.bringToFront(); } @Override protected void onPause() { // TODO Auto-generated method stub super.onPause(); glSurfaceView.onPause(); } 这个glSurfaceView.bringToFront();事实上不写也中。 在布局里写入自己定义的GLSurfaceView就ok了:
CameraActivity里仅仅负责UI部分，CameraGLSurfaceView负责开Camera、预览。并调用DirectDrawer里的draw()进行绘制。其它代码就不上了。
注意事项:
1、在onDrawFrame()里，假设不调用mDirectDrawer.draw(mtx);是啥都显示不出来的！！。这是GLSurfaceView的特别之处。
为啥呢？由于GLSurfaceView不是Android亲生的，而Surfaceview和TextureView是。所以得自己依照OpenGL ES的流程画。
2、到底mDirectDrawer.draw(mtx)里在哪获取的Buffer眼下杂家还么看太明确。貌似么有请求buffer。而是依据GLSurfaceView里创建的SurfaceTexture之前，生成的有个纹理ID。这个纹理ID一方面跟SurfaceTexture是绑定在一起的，还有一方面跟DirectDrawer绑定，而SurfaceTexture作渲染载体。
3、參考里有,有人为了解决这个问题，给出了以下三段代码:
@Overridepublic void onDrawFrame(GL10 gl){ float[] mtx = new float[16]; mSurface.updateTexImage(); mSurface.getTransformMatrix(mtx); mDirectVideo.draw(mtx);} private float[] transformTextureCoordinates( float[] coords, float[] matrix) { float[] result = new float[ coords.length ]; float[] vt = new float[4]; for ( int i = 0 ; i < coords.length ; i += 2 ) { float[] v = { coords[i], coords[i+1], 0 , 1 }; Matrix.multiplyMV(vt, 0, matrix, 0, v, 0); result[i] = vt[0]; result[i+1] = vt[1]; } return result; } textureVerticesBuffer.clear();textureVerticesBuffer.put( transformTextureCoordinates( textureVertices, mtx ));textureVerticesBuffer.position(0);我已经把代码都融入到了此demo，仅仅只是在draw()方法里么有使用。
原因是使用之后。得到的预览画面反而是变形的。而不用的话是ok的。上面的代码是得到SurfaceTexture的变换矩阵：mSurface.getTransformMatrix
然后将此矩阵传递给draw()。在draw的时候对textureVerticesBuffer作一个变化，然后再画。
下图是未加这个矩阵变换效果时:
下图为使用了变换矩阵，划片扭曲的还真说不上来咋扭曲的。但足以说明OpenGL ES在渲染效果上的强大，就是设置了个矩阵。不用一帧帧处理，就能得到不一样显示效果。
-----------------------------本文系原创。转载请注明作者yanzi1225627
版本号号:PlayCamera_V3.0.0[2014-6-22].zip
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