如何封装 opengl 流程 – 以为android-opengl-canvas例

我们在 OpenGL绘制一张图片的流程–以android-openGL-canvas为例

里看到，要使用opengl进行绘制，要实现的流程相当地繁琐，那么我们能不能对其进行封装，使绘制更加简单呢？

接下来还是以 android-openGL-canvas 为例子进行说明。

在 OpenGL绘制一张图片的流程–以android-openGL-canvas为例 里面，提到了实现的3个流程，其中第一和第二个流程是初始化的流程，基本上只需要走一遍，所以我们可以考虑将这两个流程进行封装。

封装后的类就是

EglHelper

GLThread

EglHelper

EglHelper封装了 创建 eglContext 和 创建 surface 的功能，主要的实现代码是：

public EGLContext start(EGLContext eglContext) {
if (GLThread.LOG_EGL) {
Log.w("EglHelper", "start() tid=" + Thread.currentThread().getId());
}
/*
* Get an EGL instance
*/
mEgl = (EGL10) EGLContext.getEGL();

/*
* Get to the default display.
*/
mEglDisplay = mEgl.eglGetDisplay(EGL10.EGL_DEFAULT_DISPLAY);

if (mEglDisplay == EGL10.EGL_NO_DISPLAY) {
throw new RuntimeException("eglGetDisplay failed");
}

/*
* We can now initialize EGL for that display
*/
int[] version = new int[2];
if (!mEgl.eglInitialize(mEglDisplay, version)) {
throw new RuntimeException("eglInitialize failed");
}
mEglConfig = eglConfigChooser.chooseConfig(mEgl, mEglDisplay);

/*
* Create an EGL context. We want to do this as rarely as we can, because an
* EGL context is a somewhat heavy object.
*/
mEglContext = eglContextFactory.createContext(mEgl, mEglDisplay, mEglConfig, eglContext);
if (mEglContext == null || mEglContext == EGL10.EGL_NO_CONTEXT) {
mEglContext = null;
throwEglException("createContext");
}
if (GLThread.LOG_EGL) {
Log.w("EglHelper", "createContext " + mEglContext + " tid=" + Thread.currentThread().getId());
}

mEglSurface = null;

return mEglContext;
}

public boolean createSurface(Object surface) {
if (GLThread.LOG_EGL) {
Log.w("EglHelper", "createSurface()  tid=" + Thread.currentThread().getId());
}
/*
* Check preconditions.
*/
if (mEgl == null) {
throw new RuntimeException("egl not initialized");
}
if (mEglDisplay == null) {
throw new RuntimeException("eglDisplay not initialized");
}
if (mEglConfig == null) {
throw new RuntimeException("mEglConfig not initialized");
}

/*
*  The window size has changed, so we need to create a new
*  surface.
*/
destroySurfaceImp();

/*
* Create an EGL surface we can render into.
*/
mEglSurface = eglWindowSurfaceFactory.createWindowSurface(mEgl,
mEglDisplay, mEglConfig, surface);

if (mEglSurface == null || mEglSurface == EGL10.EGL_NO_SURFACE) {
int error = mEgl.eglGetError();
if (error == EGL10.EGL_BAD_NATIVE_WINDOW) {
Log.e("EglHelper", "createWindowSurface returned EGL_BAD_NATIVE_WINDOW.");
}
return false;
}

/*
* Before we can issue GL commands, we need to make sure
* the context is current and bound to a surface.
*/
if (!mEgl.eglMakeCurrent(mEglDisplay, mEglSurface, mEglSurface, mEglContext)) {
/*
* Could not make the context current, probably because the underlying
* SurfaceView surface has been destroyed.
*/
logEglErrorAsWarning("EGLHelper", "eglMakeCurrent", mEgl.eglGetError());
return false;
}

return true;
}

可以看到两个方法的参数，说明EGLContext 和 surface 可以从外部传入。也就是说，可以和其它线程共享一个EGLContext，这样就可以使用其它线程绑定的texture了。而surface，是绘制的东西的承载者，可以是TextureView的SurfaceTexture，可以是GLSurfaceView的surfaceHolder，可以是MediaCodec的surface(用于录制视频）；所以surface的类型是Object。

GLThread

GLThread是一个继承Thread的类，我们可以不在主线程进行绘制。

主要的运行代码如下：

while (true) {
synchronized (sGLThreadManager) {
while (true) {
...
mEglContext = mEglHelper.start(mEglContext);
...
sGLThreadManager.wait();
...
}
}
...
mEglHelper.createSurface(mSurface))
...
mRenderer.onSurfaceCreated(gl, mEglHelper.getEglConfig()); // OpenGL第三步流程，绘制流程
...
mRenderer.onSurfaceChanged(gl, w, h); // OpenGL第三步流程，绘制流程
...
mRenderer.onDrawFrame(gl); // OpenGL第三步流程，绘制流程
...
}

为了支持持续不断地刷新界面，也就是RENDERMODE_CONTINUOUSLY的renderMode模式，需要在这个线程里while(true)无限循环地运行

为了支持需要时才刷新界面，也就是RENDERMODE_WHEN_DIRTY的renderMode模式，需要sGLThreadManager.wait();

public void requestRender() {
synchronized (sGLThreadManager) {
mRequestRender = true;
sGLThreadManager.notifyAll();
}
}

其中synchronized (sGLThreadManager)的部分是用于线程之间通信，外部线程可以停止和恢复这个线程

public void onResume() {
synchronized (sGLThreadManager) {
if (LOG_PAUSE_RESUME) {
Log.i("GLThread", "onResume tid=" + getId());
}
mRequestPaused = false;
mRequestRender = true;
mRenderComplete = false;
sGLThreadManager.notifyAll();
while ((!mExited) && mPaused && (!mRenderComplete)) {
if (LOG_PAUSE_RESUME) {
Log.i("Main thread", "onResume waiting for !mPaused.");
}
try {
sGLThreadManager.wait();
} catch (InterruptedException ex) {
Thread.currentThread().interrupt();
}
}
}
}

public void onPause() {
synchronized (sGLThreadManager) {
if (LOG_PAUSE_RESUME) {
Log.i("GLThread", "onPause tid=" + getId());
}
mRequestPaused = true;
sGLThreadManager.notifyAll();
while ((!mExited) && (!mPaused)) {
if (LOG_PAUSE_RESUME) {
Log.i("Main thread", "onPause waiting for mPaused.");
}
try {
sGLThreadManager.wait();
} catch (InterruptedException ex) {
Thread.currentThread().interrupt();
}
}
}
}

前文中提及的 EglHelper 和 GLThread 都是由GLSurfaceView里的内部类修改而来的，增加了从外部传入EGLContext和surface等功能，所以此处使用Builder模式，能够定制化地create一个GLThread对象。

public static class Builder {
private EGLConfigChooser configChooser;
private EGLContextFactory eglContextFactory;
private EGLWindowSurfaceFactory eglWindowSurfaceFactory;
private GLSurfaceView.Renderer renderer;
private GLWrapper mGLWrapper = null;
private int eglContextClientVersion = 2;
private int debugFlags = 0;
private int renderMode = RENDERMODE_WHEN_DIRTY;
private Object surface;
private EGLContext eglContext = EGL10.EGL_NO_CONTEXT;

public Builder setSurface(Object surface) {
this.surface = surface;
return this;
}

public Builder setEGLConfigChooser(boolean needDepth) {
setEGLConfigChooser(new SimpleEGLConfigChooser(needDepth, eglContextClientVersion));
return this;
}

public Builder setEGLConfigChooser(EGLConfigChooser configChooser) {
this.configChooser = configChooser;
return this;
}

public Builder setEGLConfigChooser(int redSize, int greenSize, int blueSize,
int alphaSize, int depthSize, int stencilSize) {
setEGLConfigChooser(new ComponentSizeChooser(redSize, greenSize,
blueSize, alphaSize, depthSize, stencilSize, eglContextClientVersion));
return this;
}

public Builder setEglContextFactory(EGLContextFactory eglContextFactory) {
this.eglContextFactory = eglContextFactory;
return this;
}

public Builder setEglWindowSurfaceFactory(EGLWindowSurfaceFactory eglWindowSurfaceFactory) {
this.eglWindowSurfaceFactory = eglWindowSurfaceFactory;
return this;
}

public Builder setRenderer(GLSurfaceView.Renderer renderer) {
this.renderer = renderer;
return this;
}

public Builder setmGLWrapper(GLWrapper mGLWrapper) {
this.mGLWrapper = mGLWrapper;
return this;
}

public Builder setEglContextClientVersion(int eglContextClientVersion) {
this.eglContextClientVersion = eglContextClientVersion;
return this;
}

public Builder setDebugFlags(int debugFlags) {
this.debugFlags = debugFlags;
return this;
}

public Builder setRenderMode(int renderMode) {
this.renderMode = renderMode;
return this;
}

public void setSharedEglContext(@NonNull EGLContext sharedEglContext) {
this.eglContext = sharedEglContext;
}

public GLThread createGLThread() {
if (renderer == null) {
throw new NullPointerException("renderer has not been set");
}
if (surface == null && eglWindowSurfaceFactory == null) {
throw new NullPointerException("surface has not been set");
}
if (configChooser == null) {
configChooser = new SimpleEGLConfigChooser(true, eglContextClientVersion);
}
if (eglContextFactory == null) {
eglContextFactory = new DefaultContextFactory(eglContextClientVersion);
}
if (eglWindowSurfaceFactory == null) {
eglWindowSurfaceFactory = new DefaultWindowSurfaceFactory();
}
return new GLThread(configChooser, eglContextFactory, eglWindowSurfaceFactory, renderer, mGLWrapper, debugFlags, renderMode, surface, eglContext);
}
}

主要关注点是configChooser, eglContextFactory, eglWindowSurfaceFactory，这3个变量分别定义了EGLConfig, EGLContext, EGLSurface。

以上就是第一第二步流程地封装。至于第三步流程，其实在 OpenGL绘制一张图片的流程–以android-openGL-canvas为例 里也已经引用了相关代码，总结就是封装成了GLES20Canvas ，有兴趣地可以进去查看。

下一篇文章会讲如何使用封装好的GLThread – 实现一个代替GLSurfaceView的GLTextureView。