android学习13——android egl hello world

通常情况下我们使用GLSurfaceview来实现opengl渲染.GLSurfaceview实现上是对SurfaceView和EGL的封装.为了从本质上理解渲染流程,使用EGL和SurfaceView来写一个Demo.

首先要封装一个EGLHelper用来操作EGL.下面代码的详细解释请参考参考资料3. EGLHelper.java代码如下:

public class EglHelper {
    EGL10 mEgl;
    EGLDisplay mEglDisplay;
    EGLSurface mEglSurface;
    EGLConfig mEglConfig;
    EGLContext mEglContext;

    public EglHelper(){}

    public void start(int[] configSpec)
    {
        mEgl = (EGL10) EGLContext.getEGL();
        mEglDisplay = mEgl.eglGetDisplay(EGL10.EGL_DEFAULT_DISPLAY);
        int[] version = new int[2];

        mEgl.eglInitialize(mEglDisplay, version);
        EGLConfig[] configs = new EGLConfig[1];
        int[] num_config = new int[1];

        mEgl.eglChooseConfig(mEglDisplay, configSpec, configs, 1,
                num_config);
        mEglConfig = configs[0];
        mEglContext = mEgl.eglCreateContext(mEglDisplay, mEglConfig,
                EGL10.EGL_NO_CONTEXT, null);
        mEglSurface = null;
    }

    public GL createSurface(SurfaceHolder holder) {
        if (mEglSurface != null) {
            mEgl.eglMakeCurrent(mEglDisplay, EGL10.EGL_NO_SURFACE,
                    EGL10.EGL_NO_SURFACE, EGL10.EGL_NO_CONTEXT);
            mEgl.eglDestroySurface(mEglDisplay, mEglSurface);
        }
        mEglSurface = mEgl.eglCreateWindowSurface(mEglDisplay,
                mEglConfig, holder, null);
        mEgl.eglMakeCurrent(mEglDisplay, mEglSurface, mEglSurface,
                mEglContext);
        GL gl = mEglContext.getGL();
        return gl;
    }

    public boolean swap() {
        mEgl.eglSwapBuffers(mEglDisplay, mEglSurface);
        return mEgl.eglGetError() != EGL11.EGL_CONTEXT_LOST;
    }

    public void finish() {
        if (mEglSurface != null) {
            mEgl.eglMakeCurrent(mEglDisplay, EGL10.EGL_NO_SURFACE,
                    EGL10.EGL_NO_SURFACE,
                    EGL10.EGL_NO_CONTEXT);
            mEgl.eglDestroySurface(mEglDisplay, mEglSurface);
            mEglSurface = null;
        }
        if (mEglContext != null) {
            mEgl.eglDestroyContext(mEglDisplay, mEglContext);
            mEglContext = null;
        }
        if (mEglDisplay != null) {
            mEgl.eglTerminate(mEglDisplay);
            mEglDisplay = null;
        }
    }
}

需要写一个类继承SurfaceView.要在SurfaceView的surfaceCreated和surfaceChanged执行之后再进行opengl的相关操作.代码如下:

public class MySurfaceView extends SurfaceView implements SurfaceHolder.Callback {
    public SurfaceHolder mHolder;
    private int w, h;
    private Context context;
    public MySurfaceView(Context context) {
        super(context);
        this.context = context;
        init();
    }

    public MySurfaceView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    private void init() {
        mHolder = getHolder();
        mHolder.addCallback(this);
    }

    @Override
    public void onWindowFocusChanged(boolean hasFocus) {
        super.onWindowFocusChanged(hasFocus);
        EglHelper eglHelper = new EglHelper();
        int[] configSpec = {
                EGL10.EGL_DEPTH_SIZE, 0,
                EGL10.EGL_NONE
        };
        eglHelper.start(configSpec);
        GL10 gl = (GL10) eglHelper.createSurface(mHolder);
        gl.glClearColor(1f, 0f, 0f, 0f);
        gl.glViewport(0, 0, w, h);
        gl.glClear(GL10.GL_COLOR_BUFFER_BIT);
        eglHelper.swap();
    }

    public void surfaceCreated(SurfaceHolder holder) {

    }

    public void surfaceDestroyed(SurfaceHolder holder) {
    }

    public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
        this.w = w;
        this.h = h;
    }
}

整个程序源代码: https://github.com/zhouyang209117/AndroidTutorial/tree/master/OpenGL/EGLHelloWorld

参考资料

1. Sayed Y, Hashimi, Satya Komatineni. Pro Android. Apress. pp325-362. 2009.
2. (美)Kevin Brothaler著, 刘力平,苏统华译. OpenGL ES应用开发实践指南 android卷. 机械工业出版社. pp1-26. 2014.
3. Aaftab Munshi, Dan Ginsburg, Dave Shreiner. OpenGL ES 2.0 Programming Guide. addison wesley. pp35-56