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

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

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：

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

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：

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

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

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

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