阅读本文前如果是初次接触opengl可以先阅读前文:
openGL 3D图形和openGL简介：
http://blog.csdn.net/pangrui201/article/details/75091501
android上opengl es基础知识
Google在Android2.2 以后支持 opengl es 2.2,在Android 4.3以后引入opengl es 3.0。Android中使用openGL会用到GLSurfaceView控件， GLSurfaceView.Renderer，在Android studio的debug模式下我们可以清楚的看到Renderer的各个回调函数发生在非UI主线程，即渲染线程,具体渲染是在一块称为”surface”(在openGL里面称为ViewPort视口)的地方完成，渲染绘制完成后在将渲染结果直接在主线程显示，实际上GLSurfaceView在View Hierarchy上”穿洞”，让底层open gl surface显示出来。同时，需要考虑GLSurfaceView和Activity的各个生命周期的问题。
另一方面，在Android 4.0以后提供了一个纹理视图(TextureView)可以也可以渲染opengl，TextureView像普通view一样不在需要”穿洞”了，但是TextureView没有内置opengl的初始化操作。
第一个opengl es程序
如下代码是在Android studio上创建的第一个opengl es项目:
public class MainActivity extends AppCompatActivity {
private GLSurfaceView glSurfaceView;
private boolean rendererSet;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
glSurfaceView = new GLSurfaceView(this);
// Check if the system supports OpenGL ES 2.0.
final ActivityManager activityManager =
(ActivityManager) getSystemService(Context.ACTIVITY_SERVICE);
final ConfigurationInfo configurationInfo =
activityManager.getDeviceConfigurationInfo();
/*
final boolean supportsEs2 = configurationInfo.reqGlEsVersion >= 0x20000;
*/
// Even though the latest emulator supports OpenGL ES 2.0,
// it has a bug where it doesn't set the reqGlEsVersion so
// the above check doesn't work. The below will detect if the
// app is running on an emulator, and assume that it supports
// OpenGL ES 2.0.
final boolean supportsEs2 =
configurationInfo.reqGlEsVersion >= 0x20000
|| (Build.VERSION.SDK_INT >= Build.VERSION_CODES.ICE_CREAM_SANDWICH_MR1
&& (Build.FINGERPRINT.startsWith("generic")
|| Build.FINGERPRINT.startsWith("unknown")
|| Build.MODEL.contains("google_sdk")
|| Build.MODEL.contains("Emulator")
|| Build.MODEL.contains("Android SDK built for x86")));
if (supportsEs2) {
// Request an OpenGL ES 2.0 compatible context.
glSurfaceView.setEGLContextClientVersion(2);
// Assign our renderer.
glSurfaceView.setRenderer(new FirstOpenGLProjectRenderer());
rendererSet = true;
} else {
/*
* This is where you could create an OpenGL ES 1.x compatible
* renderer if you wanted to support both ES 1 and ES 2. Since we're
* not doing anything, the app will crash if the device doesn't
* support OpenGL ES 2.0. If we publish on the market, we should
* also add the following to AndroidManifest.xml:
*
* <uses-feature android:glEsVersion="0x00020000"
* android:required="true" />
*
* This hides our app from those devices which don't support OpenGL
* ES 2.0.
*/
Toast.makeText(this, "This device does not support OpenGL ES 2.0.",
Toast.LENGTH_LONG).show();
return;
}
setContentView(glSurfaceView);
}
@Override
protected void onPause() {
super.onPause();
if (rendererSet) {
glSurfaceView.onPause();
}
}
@Override
protected void onResume() {
super.onResume();
if (rendererSet) {
glSurfaceView.onResume();
}
}
}
supportsEs2 = configurationInfo.reqGlEsVersion >= 0x20000;是用来判断是否支持opengl es2.0,同时在模拟器的话可能支持不是多好，所以代码进行了判断。 glSurfaceView.setEGLContextClientVersion(2);是来具体设置opengl版本，配置surface视图。同时需要注意Activity的生命周期需要回调glSurfaceView对应的生命周期，这样surface视图才能正确处理渲染线程暂停和继续，同时释放和续用opengl的上下文。
下面是FirstOpenGLProjectRenderer 的代码：
public class FirstOpenGLProjectRenderer implements Renderer {
@Override
public void onSurfaceCreated(GL10 glUnused, EGLConfig config) {
// Set the background clear color to red. The first component is
// red, the second is green, the third is blue, and the last
// component is alpha, which we don't use in this lesson.
glClearColor(1.0f, 0.0f, 0.0f, 0.0f);
}
/**
* onSurfaceChanged is called whenever the surface has changed. This is
* called at least once when the surface is initialized. Keep in mind that
* Android normally restarts an Activity on rotation, and in that case, the
* renderer will be destroyed and a new one created.
*
* @param width
* The new width, in pixels.
* @param height
* The new height, in pixels.
*/
@Override
public void onSurfaceChanged(GL10 glUnused, int width, int height) {
// Set the OpenGL viewport to fill the entire surface.
glViewport(0, 0, width, height);
}
/**
* OnDrawFrame is called whenever a new frame needs to be drawn. Normally,
* this is done at the refresh rate of the screen.
*/
@Override
public void onDrawFrame(GL10 glUnused) {
// Clear the rendering surface.
glClear(GL_COLOR_BUFFER_BIT);
}
}主要有三个回调方法，onSurfaceCreated，onSurfaceChanged，onDrawFrame。之前已经说过了，这些方法回调发生在渲染线程。onSurfaceCreated是在surface被创建时，GLSurfaceView会回调这个方法。onSurfaceChanged是在surface被创建后每次在surface尺寸发生变化的时候GLSurfaceView会回调，比如横竖屏切换会回调这个方法。onDrawFrame是当每绘制一帧就会被GLSurfaceView回调，通常一定要在这个方法里做点事情哪怕是设置清屏颜色，因为这个方法调用之后会把渲染结果surface给屏幕显示，不能说什么都没有，这样的话可能会显示花屏。另外,通常GLSurfaceView会以显示屏的的刷新频率来回调onDrawFrame进行渲染，当然我们可以设置GLSurfaceView的渲染模式来修改，调用
glSurfaceView.setRenderMode(GLSurfaceView.RENDERMODE_WHEN_DIRTY);
//GLSurfaceView.RENDERMODE_CONTINUOUSLY:持续渲染(默认)
//GLSurfaceView.RENDERMODE_WHEN_DIRTY:脏渲染,命令渲染；即有两种渲染模式脏渲染和持续渲染(默认)。使用脏渲染需要和glSurfaceView.requestRender配合使用。
综上分析，在onSurfaceCreated里需要设置清屏色，本文为红色 glClearColor(1.0f, 0.0f, 0.0f, 0.0f);在onSurfaceChanged里设置视口viewport大小即通知opengl需要渲染视口大小即surface大小。注意：视口viewport是opengl里面的概念，surface是GLSurfaceView里提供给底层渲染显示的区域，故可以理解为同一个。在onDrawFrame里面 glClear(GL_COLOR_BUFFER_BIT);是清楚所有颜色缓冲器，这样就会显示清屏色即 glClearColor(1.0f, 0.0f, 0.0f, 0.0f)设置的红色。
到此，本文章结束。主要讲解基础概念，基础原理。本文代码地址:
https://github.com/pangrui201/OpenGlesProject/tree/master/OpenGlesProject_lesson1
