OpenGL ES EGL

几个相似的概念

OpenCV

从图像到数据，提供图像处理和视频处理的基础算法库，还涉及一些机器学习的算法，比如人机互动，物体识别，人脸识别，动作识别，运动跟踪，运动分析，汽车安全驾驶
OpenGL

从数据到图像，主要用于生成二维、三维图像，绘制合适的视觉图像给人看
OpenGL ES

OpenGL的子集，删减了一些低效的操作方式，但兼容性也更差一点
WebGL

基于 OpenGL ES 2.0 的 Javascript API，用于Web浏览器呈现交互式3D图形
Vulkan

免费开放的、跨平台的、底层的图形 API，旨在取代OpenGL
DirectX

windows平台上提升多媒体程序执行效率的API，就它不是跨平台的

OpenGL ES的使用场景

图片处理。比如图片色调转换、美颜等。视频滤镜、音频滤镜.
摄像头预览效果处理。比如美颜相机、恶搞相机等。
视频处理。摄像头预览效果处理可以，这个自然也不在话下了。
3D 游戏。比如神庙逃亡、都市赛车等。

EGL 是渲染 API（如 OpenGL ES）和原生窗口系统之间的接口

不同平台有不同的EGL系统，windows上是WGL，Linux上是GLX，Apple OS上是AGL

EGL绘图步骤

获取 EGLDisplay 对象：eglGetDisplay()
初始化与 EGLDisplay 之间的连接：eglInitialize()
获取 EGLConfig 对象：eglChooseConfig()
创建 EGLContext 实例：eglCreateContext()
创建 EGLSurface 实例：eglCreateWindowSurface()
连接 EGLContext 和 EGLSurface：eglMakeCurrent()
使用 OpenGL ES API 绘制图形：gl_*()
切换 front buffer 和 back buffer 送显：eglSwapBuffer()
断开并释放与 EGLSurface 关联的 EGLContext 对象：eglMakeCurrent(mDisplay, EGL_NO_SURFACE, EGL_NO_SURFACE, EGL_NO_CONTEXT);
删除 EGLSurface 对象：eglDestroySurface()
删除 EGLContext 对象：eglDestroyContext()
终止与 EGLDisplay 之间的连接：eglTerminate(EGLDisplay)
释放线程：eglReleaseThread()

示例代码

#include "ViceScreenDisplay.h"

namespace android {

static const char* kSystemAssets = "/system/etc/mmi/";

sp<SurfaceComposerClient> ViceScreenDisplay::session(){
    return mSession;
}


int ViceScreenDisplay::readyToshow(){
    //first ref
    mSession = new SurfaceComposerClient();
    status_t err = mSession->linkToComposerDeath(this);
    SLOGE_IF(err, "linkToComposerDeath failed (%s) ", strerror(-err));
    if (err == NO_ERROR) {
        // Load the animation content -- this can be slow (eg 200ms)
        // called before waitForSurfaceFlinger() in main() to avoid wait
        ALOGD(" mSession->linkToComposerDeath NO_ERROR");
    }

    const char* root = getenv("ANDROID_ROOT");
    String8 path(root);
    path.appendPath(kSystemAssets);
    mAssets.addAssetPath(path, NULL, false /* appAsLib */, true /* isSystemAsset */);
    ALOGD("readyToshow Assets path = %s",path.string());

    const auto displayIds = SurfaceComposerClient::getPhysicalDisplayIds();
    ALOGD("runToshow displayIds = %d",(int)displayIds.size());

    mDisplayToken = SurfaceComposerClient::getPhysicalDisplayToken(displayIds[1]);

    if (mDisplayToken == nullptr){
        ALOGD("runToshow mDisplayToken is nullptr");
        return -1;
    }

    DisplayInfo dinfo;
    status_t status = SurfaceComposerClient::getDisplayInfo(mDisplayToken, &dinfo);
    if (status)
        return -1;

    // create the native surface
    control = session()->createSurface(String8("showAtVice"),
            dinfo.w, dinfo.h, PIXEL_FORMAT_RGB_565);

    SurfaceComposerClient::Transaction t;
    layer_state_t* ls = t.getLayerState(control);
    DisplayState& ds(t.getDisplayState(mDisplayToken));

    ALOGD("runToshow layerStack %d",ds.layerStack);
    while(ds.layerStack != 4096){
        ds = t.getDisplayState(mDisplayToken);
        t.setLayerStack(control, 4096);
        t.setDisplayLayerStack(mDisplayToken,4096);
        Rect viceRect(0,0,1920,1280);
        t.setDisplayProjection(mDisplayToken,0,viceRect,viceRect);
        ALOGD("runToshow get the layerStack %d  layerstate %d",ds.layerStack,ls->layerStack);
    }

    t.setLayer(control, 0x40000000)
        .apply();
    sp<Surface> s = control->getSurface();

    // initialize opengl and egl
    const EGLint attribs[] = {
            EGL_RED_SIZE,   8,
            EGL_GREEN_SIZE, 8,
            EGL_BLUE_SIZE,  8,
            EGL_DEPTH_SIZE, 0,
            EGL_NONE
    };
    EGLint w, h;
    EGLint numConfigs;
    EGLConfig config;
    EGLSurface surface;
    EGLContext context;

    //1.获取显示设备，使用默认的渲染类型
    EGLDisplay display = eglGetDisplay(EGL_DEFAULT_DISPLAY);
    if (display == EGL_NO_DISPLAY || eglGetError() != EGL_SUCCESS)
        ALOGD("eglGetDisplay fail");
    else
        ALOGD("eglGetDisplay success");
    //2.初始化EGL
    EGLBoolean initialize = eglInitialize(display, nullptr, nullptr);
    //3.自定义配置
    eglChooseConfig(display, attribs, &config, 1, &numConfigs);
    //5.创建窗口渲染区域，相当于创建画布，用户想要绘制的信息都要先绘制到EGLSurface上，然后通过EGLDisplay显示
    surface = eglCreateWindowSurface(display, config, s.get(), nullptr);
    //4.创建上下文对象，该对象包含了操作所需要的所有状态信息，没有该对象，OpenGL指令就没有执行的环境
    context = eglCreateContext(display, config, nullptr, nullptr);
    //获取画布的宽高
    eglQuerySurface(display, surface, EGL_WIDTH, &w);
    eglQuerySurface(display, surface, EGL_HEIGHT, &h);
    //6.将创建的surface,display,context进行绑定，连接，因为一个应用程序可能创建多个context
    if (eglMakeCurrent(display, surface, surface, context) == EGL_FALSE)
        return NO_INIT;

    mDisplay = display;
    mContext = context;
    mSurface = surface;
    mWidth = w;
    mHeight = h;
    mFlingerSurfaceControl = control;
    mFlingerSurface = s;
    mTargetInset = -1;

    return 0;
}

int ViceScreenDisplay::clear(){

    ALOGD("clear");
	//9.将surface,display,context解绑
    eglMakeCurrent(mDisplay, EGL_NO_SURFACE, EGL_NO_SURFACE, EGL_NO_CONTEXT);
    //11.销毁context
    eglDestroyContext(mDisplay, mContext);
    //10.销毁surface
    eglDestroySurface(mDisplay, mSurface);
    mFlingerSurface.clear();
    mFlingerSurfaceControl.clear();
    //12.终止显示
    eglTerminate(mDisplay);
    //13.释放线程
    eglReleaseThread();
    return 0;
}

int ViceScreenDisplay::runToshow(){

    initTexture(&mAndroid[0], mAssets, "fct-display.png");
    ALOGD("init texture result,mAndroid[0].w=%d, mAndroid[0].h=%d, mAndroid[0].name=%u ",mAndroid[0].w,mAndroid[0].h,mAndroid[0].name);

    // clear screen
    glShadeModel(GL_FLAT);
    glDisable(GL_DITHER);
    glDisable(GL_SCISSOR_TEST);
    glClearColor(0,0,0,1);
    glClear(GL_COLOR_BUFFER_BIT); 
    eglSwapBuffers(mDisplay, mSurface);

    glEnable(GL_TEXTURE_2D);
    glTexEnvx(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);

    const GLint xc = (mWidth  - mAndroid[0].w) / 2;
    const GLint yc = (mHeight - mAndroid[0].h) / 2;
    const Rect updateRect(xc, yc, xc + mAndroid[0].w, yc + mAndroid[0].h);

    glScissor(updateRect.left, mHeight - updateRect.bottom, updateRect.width(),
            updateRect.height());

    // Blend state
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
    glTexEnvx(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);

    while(1) {
       glDisable(GL_SCISSOR_TEST);
       glClear(GL_COLOR_BUFFER_BIT);
       glEnable(GL_SCISSOR_TEST);
       glDisable(GL_BLEND);
       glEnable(GL_BLEND);
       glBindTexture(GL_TEXTURE_2D, mAndroid[0].name);
       //7.绘制图形
       glDrawTexiOES(xc, yc, 0, mAndroid[0].w, mAndroid[0].h);
       //ALOGD("drawing graphic,mDisplay:%s, mSurface:%s",mDisplay,mSurface);
       //8.将EGLSurface中的数据交换到EGLDisplay，将绘制的内容输出到屏幕进行显示
       ALOGD("   start drawing...");
       EGLBoolean res = eglSwapBuffers(mDisplay, mSurface);
       ALOGD("   drawing result,res:%u",res);
       if (res == EGL_FALSE){
           ALOGD("   drawing false");
           break;
       } else if (res == EGL_TRUE){
           ALOGD("   drawing success");
       } else {
           ALOGD("   drawing unknown");
       }
    }
    glDeleteTextures(1, &mAndroid[0].name);
    return 0;
}

status_t ViceScreenDisplay::initTexture(Texture* texture, AssetManager& assets,
        const char* name) {
    Asset* asset = assets.open(name, Asset::ACCESS_BUFFER);
    if (asset == nullptr){
        ALOGD("initTexture NO_INIT");
        return NO_INIT;
    }
    SkBitmap bitmap;
    sk_sp<SkData> data = SkData::MakeWithoutCopy(asset->getBuffer(false),
            asset->getLength());
    sk_sp<SkImage> image = SkImage::MakeFromEncoded(data);
    image->asLegacyBitmap(&bitmap, SkImage::kRO_LegacyBitmapMode);
    asset->close();
    delete asset;

    const int w = bitmap.width();
    const int h = bitmap.height();
    const void* p = bitmap.getPixels();

    GLint crop[4] = { 0, h, w, -h };
    texture->w = w;
    texture->h = h;

    glGenTextures(1, &texture->name);
    glBindTexture(GL_TEXTURE_2D, texture->name);

    switch (bitmap.colorType()) {
        case kAlpha_8_SkColorType:
            glTexImage2D(GL_TEXTURE_2D, 0, GL_ALPHA, w, h, 0, GL_ALPHA,
                    GL_UNSIGNED_BYTE, p);
            break;
        case kARGB_4444_SkColorType:
            glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, w, h, 0, GL_RGBA,
                    GL_UNSIGNED_SHORT_4_4_4_4, p);
            break;
        case kN32_SkColorType:
            glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, w, h, 0, GL_RGBA,
                    GL_UNSIGNED_BYTE, p);
            break;
        case kRGB_565_SkColorType:
            glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, w, h, 0, GL_RGB,
                    GL_UNSIGNED_SHORT_5_6_5, p);
            break;
        default:
            break;
    }

    glTexParameteriv(GL_TEXTURE_2D, GL_TEXTURE_CROP_RECT_OES, crop);
    glTexParameterx(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameterx(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexParameterx(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    glTexParameterx(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);

    return NO_ERROR;
}

void ViceScreenDisplay::binderDied(const wp<IBinder>&)
{
    // woah, surfaceflinger died!
    ALOGD("SurfaceFlinger died, exiting...");

    // calling requestExit() is not enough here because the Surface code
    // might be blocked on a condition variable that will never be updated.
    kill( getpid(), SIGKILL );
}

ViceScreenDisplay::~ViceScreenDisplay() {

    ALOGD("~ViceScreenDisplay");
}

}
;// namespace android

OpenGL ES EGL

几个相似的概念

OpenGL ES的使用场景

OpenGL ES EGL

EGL绘图步骤

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