【Android OpenGL ES】阅读hello-gl2代码（三）配置EGL

电玩女神 2022-01-05 19:35 225阅读 0赞

关于EGL的介绍：

EGL is an interface between Khronos rendering APIs such as OpenGL ES or OpenVG and the underlying native platform window system. It handles graphics context management, surface/buffer binding, and rendering synchronization and enables high-performance, accelerated, mixed-mode 2D and 3D rendering using other Khronos APIs. EGL also provides interop capability between Khronos to enable efficient transfer of data between APIs – for example between a video subsystem running OpenMAX AL and a GPU running OpenGL ES.

EGL can be implemented on multiple operating systems (such as Android and Linux) and native window systems (such as X and Microsoft Windows). Implementations may also choose to allow rendering into specific types of EGL surfaces via other supported native rendering APIs, such as Xlib or GDI. EGL provides:

*  Mechanisms for creating rendering surfaces (windows, pbuffers, pixmaps) onto which client APIs can draw and share
 *  Methods to create and manage graphics contexts for client APIs
 *  Ways to synchronize drawing by client APIs as well as native platform rendering APIs.

官网：[http://www.khronos.org/egl][http_www.khronos.org_egl]

**ConfigChooser**

定义配置信息的属性列表：

private static int EGL_OPENGL_ES2_BIT = 4;
    private static int[] s_configAttribs2 =
    {
        EGL10.EGL_RED_SIZE, 4,
        EGL10.EGL_GREEN_SIZE, 4,
        EGL10.EGL_BLUE_SIZE, 4,
        EGL10.EGL_RENDERABLE_TYPE, EGL_OPENGL_ES2_BIT,
        EGL10.EGL_NONE
    };

配置EGL\_RED\_SIZE、EGL\_GREEN\_SIZE、EGL\_BLUE\_SIZE和EGL\_RENDERABLE\_TYPE。

EGL的属性列表：

![2012110610430652.png][]

public EGLConfig chooseConfig(EGL10 egl, EGLDisplay display) {
    
        /* Get the number of minimally matching EGL configurations
         */
        int[] num_config = new int[1];
        egl.eglChooseConfig(display, s_configAttribs2, null, 0, num_config);
    
        int numConfigs = num_config[0];
    
        if (numConfigs <= 0) {
            throw new IllegalArgumentException("No configs match configSpec");
        }
    
        /* Allocate then read the array of minimally matching EGL configs
         */
        EGLConfig[] configs = new EGLConfig[numConfigs];
        egl.eglChooseConfig(display, s_configAttribs2, configs, numConfigs, num_config);
    
        if (DEBUG) {
             printConfigs(egl, display, configs);
        }
        /* Now return the "best" one
         */
        return chooseConfig(egl, display, configs);
    }

GLSurfaceView.EGLConfigChooser：[http://developer.android.com/reference/android/opengl/GLSurfaceView.EGLConfigChooser.html][http_developer.android.com_reference_android_opengl_GLSurfaceView.EGLConfigChooser.html]

首先，获得调用*egl.eglChooseConfig(display, s\_configAttribs2, null, 0, num\_config);*，获得配置信息的数量；

然后，调用egl.eglChooseConfig(display, s\_configAttribs2, configs, numConfigs, num\_config);，获得配置信息EGLConfig数组；

最后，调用私有方法chooseConfig(egl, display, configs);，取得最合适的配置信息EGLConfig。

EGL配置管理如下图：

![2012110611120057.png][]

**ContextFactory**

在EGL2JNIView.java文件中，私有内部类ConfigChooser定义如下：

private static class ContextFactory implements GLSurfaceView.EGLContextFactory {
        private static int EGL_CONTEXT_CLIENT_VERSION = 0x3098;
        public EGLContext createContext(EGL10 egl, EGLDisplay display, EGLConfig eglConfig) {
            Log.w(TAG, "creating OpenGL ES 2.0 context");
            checkEglError("Before eglCreateContext", egl);
            int[] attrib_list = {EGL_CONTEXT_CLIENT_VERSION, 2, EGL10.EGL_NONE };
            EGLContext context = egl.eglCreateContext(display, eglConfig, EGL10.EGL_NO_CONTEXT, attrib_list);
            checkEglError("After eglCreateContext", egl);
            return context;
        }
    
        public void destroyContext(EGL10 egl, EGLDisplay display, EGLContext context) {
            egl.eglDestroyContext(display, context);
        }
    }

GLSurfaceView.EGLContextFactory：[http://developer.android.com/reference/android/opengl/GLSurfaceView.EGLContextFactory.html][http_developer.android.com_reference_android_opengl_GLSurfaceView.EGLContextFactory.html]

*int\[\] attrib\_list = \{EGL\_CONTEXT\_CLIENT\_VERSION, 2, EGL10.EGL\_NONE \};*  
*EGLContext context = egl.eglCreateContext(display, eglConfig, EGL10.EGL\_NO\_CONTEXT, attrib\_list);*

创建OpenGL ES 2.0版本的EGLContext。

转载于:https://www.cnblogs.com/dyingbleed/archive/2012/11/05/2755529.html

[http_www.khronos.org_egl]: http://www.khronos.org/egl
[2012110610430652.png]: /images/20211228/2626bb5cd6684c5c850c3853bdd41bba.png
[http_developer.android.com_reference_android_opengl_GLSurfaceView.EGLConfigChooser.html]: http://developer.android.com/reference/android/opengl/GLSurfaceView.EGLConfigChooser.html
[2012110611120057.png]: /images/20211228/c4b9e270289a47a0940bada1ac8f4ef0.png
[http_developer.android.com_reference_android_opengl_GLSurfaceView.EGLContextFactory.html]: http://developer.android.com/reference/android/opengl/GLSurfaceView.EGLContextFactory.html