EGLHelper

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本文详细介绍了EGLHelper类在Android应用中初始化EGL、创建OpenGL表面、交换缓冲区等关键操作的过程，提供了实现高效图形渲染的技术细节。

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import javax.microedition.khronos.egl.EGL10;
import javax.microedition.khronos.egl.EGL11;
import javax.microedition.khronos.egl.EGLConfig;
import javax.microedition.khronos.egl.EGLContext;
import javax.microedition.khronos.egl.EGLDisplay;
import javax.microedition.khronos.egl.EGLSurface;
import javax.microedition.khronos.opengles.GL;

import android.view.SurfaceHolder;

/**
 * Copyright (C) 2008 Google Inc.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 * 
 * EGLHelper class extracted from GLView
 */

public class EGLHelper
{
        publicEGLHelper()
        {

        }

        /**
         * Initialize EGL for a given configuration spec.
         * 
         * @param configSpec
         */
        publicvoid start(int[] configSpec)
        {
                /*
                 * Get an EGL instance
                 */
                mEgl =(EGL10)EGLContext.getEGL();

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

                /*
                 * We can now initialize EGL for that 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];

                /*
                 * Create an OpenGL ES context. This must be done only once, an OpenGL
                 * context is a somewhat heavy object.
                 */
                mEglContext = mEgl.eglCreateContext(mEglDisplay, mEglConfig,
                                EGL10.EGL_NO_CONTEXT,null);

                mEglSurface =null;
        }

        /*
         * Create and return an OpenGL surface
         */
        public GL createSurface(SurfaceHolder holder)
        {
                /*
                 * The window size has changed, so we need to create a new surface.
                 */
                if(mEglSurface!=null)
                {

                        /*
                         * Unbind and destroy the old EGL surface, if there is one.
                         */
                        mEgl.eglMakeCurrent(mEglDisplay, EGL10.EGL_NO_SURFACE,
                                        EGL10.EGL_NO_SURFACE, EGL10.EGL_NO_CONTEXT);
                        mEgl.eglDestroySurface(mEglDisplay, mEglSurface);
                }

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

                /*
                 * Before we can issue GL commands, we need to make sure the context is
                 * current and bound to a surface.
                 */
                mEgl.eglMakeCurrent(mEglDisplay, mEglSurface, mEglSurface, mEglContext);
                if(mEgl.eglGetError()==EGL11.EGL_CONTEXT_LOST)
                        AngleMainEngine.mDirty=true;

                GL gl = mEglContext.getGL();
                return gl;
        }

        /**
         * Display the current render surface.
         * 
         * @return false if the context has been lost.
         */
        publicboolean swap()
        {
                mEgl.eglSwapBuffers(mEglDisplay, mEglSurface);

                /*
                 * Always check for EGL_CONTEXT_LOST, which means the context and all
                 * associated data were lost (For instance because the device went to
                 * sleep). We need to sleep until we get a new surface.
                 */
                return mEgl.eglGetError()!= EGL11.EGL_CONTEXT_LOST;
        }

        publicvoid finish()
        {
                boolean success=true;
                if(mEglSurface!=null)
                {
                        success&=mEgl.eglMakeCurrent(mEglDisplay, EGL10.EGL_NO_SURFACE,
                                        EGL10.EGL_NO_SURFACE, EGL10.EGL_NO_CONTEXT);
                        success&=mEgl.eglDestroySurface(mEglDisplay, mEglSurface);
                        mEglSurface =null;
                }
                if(mEglContext!=null)
                {
                        success&=mEgl.eglDestroyContext(mEglDisplay, mEglContext);
                        mEglContext =null;
                }
                if(mEglDisplay!=null)
                {
                        success&=mEgl.eglTerminate(mEglDisplay);
                        mEglDisplay =null;
                }
                AngleMainEngine.mDirty=!success;
        }

        EGL10 mEgl;
        EGLDisplay mEglDisplay;
        EGLSurface mEglSurface;
        EGLConfig mEglConfig;
        EGLContext mEglContext;
}

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