Android開始開放C/C++編寫的應用

對於Android平台來說已經有跡象表明開放純C/C++編寫的應用，過去我們也介紹過今天就說下具體的吧，在NDK的Samples中名為native-activity的例子已經證實了這點，不過目前Android123提示大家，顯示系統Android上提供的C++接口只有OpenGL了，一起來看看androidManifest.XML中的定義吧。不過必須在Android 2.2或更高的固件上才能運行。注意下面的minSDK設置的為8，同時application的android:hasCode=false表示了這個應用將沒有Java代碼。 

  <?XML version="1.0" encoding="utf-8"?>
<manifest XMLns:android="http://schemas.android.com/apk/res/android"
        package="com.example.native_activity"
        android:versionCode="1"
        android:versionName="1.0">

    <uses-sdk android:minSdkVersion="8" />

       <application android:label="@string/app_name" android:hasCode="false">

            <activity android:name="android.app.NativeActivity"
                android:label="@string/app_name" android:configChanges="orIEntation|keyboardHidden">
                <meta-data android:name="android.app.lib_name" android:value="native-activity" />
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

 從上面來看activity對應的name必須是android.app.NativeActivity，這點和AIDL中Service的name也寫全package name是一個道理，否則無法找到。下面是純C++的JNI代碼了

#include <jni.h>
#include <errno.h>

#include <EGL/egl.h>   //這裡JNI目前提供的支持，不是很多，只有GL家族作為顯示系統了
#include <GLES/gl.h>

#include <android/sensor.h> //感應器的支持
#include <android/log.h>
#include <android_native_app_glue.h>  //這裡android123提示大家，c程序必須從main開始，這裡必須包含這個，經過改進的偽入口點了。

#define LOGI(...) ((void)__android_log_print(android_LOG_INFO, "native-activity", __VA_ARGS__))
#define LOGW(...) ((void)__android_log_print(android_LOG_WARN, "native-activity", __VA_ARGS__))

struct saved_state {
    float angle;
    int32_t x;
    int32_t y;
};

struct engine {
    struct android_app* app;

    ASensorManager* sensorManager;
    const ASensor* accelerometerSensor;
    ASensorEventQueue* sensorEventQueue;

    int animating;
    EGLDisplay display;
    EGLSurface surface;
    EGLContext context;
    int32_t width;
    int32_t height;
    struct saved_state state;
};

初始化OpenGL ES

static int engine_init_display(struct engine* engine) {
    const EGLint attribs[] = {
            EGL_SURFACE_TYPE, EGL_WINDOW_BIT,
            EGL_BLUE_SIZE, 8,
            EGL_GREEN_SIZE, 8,
            EGL_RED_SIZE, 8,
            EGL_NONE
    };
    EGLint w, h, dummy, format;
    EGLint numConfigs;
    EGLConfig config;
    EGLSurface surface;
    EGLContext context;

    EGLDisplay display = eglGetDisplay(EGL_DEFAULT_DISPLAY);

    eglInitialize(display, 0, 0);

    eglChooseConfig(display, attribs, &config, 1, &numConfigs);

    eglGetConfigAttrib(display, config, EGL_NATIVE_VISUAL_ID, &format);

    ANativeWindow_setBuffersGeometry(engine->app->window, 0, 0, format);

    surface = eglCreateWindowsurface(display, config, engine->app->window, NULL);
    context = eglCreateContext(display, config, NULL, NULL);

    if (eglMakeCurrent(display, surface, surface, context) == EGL_FALSE) {
        LOGW("Unable to eglMakeCurrent");
        return -1;
    }

    eglQuerySurface(display, surface, EGL_WIDTH, &w);
    eglQuerySurface(display, surface, EGL_HEIGHT, &h);

    engine->display = display;
    engine->context = context;
    engine->surface = surface;
    engine->width = w;
    engine->height = h;
    engine->state.angle = 0;

    glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_FASTEST);
    glEnable(GL_CULL_FACE);
    glShadeModel(GL_SMOOTH);
    glDisable(GL_DEPTH_TEST);

    return 0;
}

static void engine_draw_frame(struct engine* engine) {
    if (engine->display == NULL) {
        // No display.
        return;
    }

    glClearColor(((float)engine->state.x)/engine->width, engine->state.angle,
            ((float)engine->state.y)/engine->height, 1);
    glClear(GL_COLOR_BUFFER_BIT);

    eglSwapBuffers(engine->display, engine->surface);
}

static void engine_term_display(struct engine* engine) {
    if (engine->display != EGL_NO_DISPLAY) {
        eglMakeCurrent(engine->display, EGL_NO_SURFACE, EGL_NO_SURFACE, EGL_NO_CONTEXT);
        if (engine->context != EGL_NO_CONTEXT) {
            eglDestroyContext(engine->display, engine->context);
        }
        if (engine->surface != EGL_NO_SURFACE) {
            eglDestroySurface(engine->display, engine->surface);
        }
        eglTerminate(engine->display);
    }
    engine->animating = 0;
    engine->display = EGL_NO_DISPLAY;
    engine->context = EGL_NO_CONTEXT;
    engine->surface = EGL_NO_SURFACE;
}

static int32_t engine_handle_input(struct android_app* app, AInputEvent* event) {
    struct engine* engine = (struct engine*)app->userData;
    if (AInputEvent_getType(event) == AINPUT_EVENT_TYPE_MOTION) {
        engine->animating = 1;
        engine->state.x = AMotionEvent_getX(event, 0);
        engine->state.y = AMotionEvent_getY(event, 0);
        return 1;
    }
    return 0;
}

static void engine_handle_cmd(struct android_app* app, int32_t cmd) {
    struct engine* engine = (struct engine*)app->userData;
    switch (cmd) {
        case APP_CMD_SAVE_STATE:
            engine->app->savedState = malloc(sizeof(struct saved_state));
            *((struct saved_state*)engine->app->savedState) = engine->state;
            engine->app->savedStateSize = sizeof(struct saved_state);
            break;
        case APP_CMD_INIT_WINDOW:
            if (engine->app->window != NULL) {
                engine_init_display(engine);
                engine_draw_frame(engine);
            }
            break;
        case APP_CMD_TERM_WINDOW:
            engine_term_display(engine);
            break;
        case APP_CMD_GAINED_FOCUS:
            if (engine->accelerometerSensor != NULL) {
                ASensorEventQueue_enableSensor(engine->sensorEventQueue,
                        engine->accelerometerSensor);
                ASensorEventQueue_setEventRate(engine->sensorEventQueue,
                        engine->accelerometerSensor, (1000L/60)*1000);
            }
            break;
        case APP_CMD_LOST_FOCUS:
            if (engine->accelerometerSensor != NULL) {
                ASensorEventQueue_disableSensor(engine->sensorEventQueue,
                        engine->accelerometerSensor);
            }
            engine->animating = 0;
            engine_draw_frame(engine);
            break;
    }
}

void android_main(struct android_app* state) {  //這裡是偽main入口點，但是所有的初始化的確從這裡開始
    struct engine engine;

    app_dummy();

    memset(&engine, 0, sizeof(engine));
    state->userData = &engine;
    state->onAppCmd = engine_handle_cmd;
    state->onInputEvent = engine_handle_input;
    engine.app = state;

    engine.sensorManager = ASensorManager_getInstance();
    engine.accelerometerSensor = ASensorManager_getDefaultSensor(engine.sensorManager,
            ASENSOR_TYPE_ACCELEROMETER);
    engine.sensorEventQueue = ASensorManager_createEventQueue(engine.sensorManager,
            state->looper, LOOPER_ID_USER, NULL, NULL);

    if (state->savedState != NULL) {
        // We are starting with a previous saved state; restore from it.
        engine.state = *(struct saved_state*)state->savedState;
    }

    // loop waiting for stuff to do.

    while (1) {
        // Read all pending events.
        int ident;
        int events;
        struct android_poll_source* source;

        // If not animating, we will block forever waiting for events.
        // If animating, we loop until all events are read, then continue
        // to draw the next frame of animation.
        while ((ident=ALooper_pollAll(engine.animating ? 0 : -1, NULL, &events,
                (void**)&source)) >= 0) {

            // Process this event.
            if (source != NULL) {
                source->process(state, source);
            }

            // If a sensor has data, process it now.
            if (ident == LOOPER_ID_USER) {
                if (engine.accelerometerSensor != NULL) {
                    ASensorEvent event;
                    while (ASensorEventQueue_getEvents(engine.sensorEventQueue,
                            &event, 1) > 0) {
                        LOGI("accelerometer: x=%f y=%f z=%f",
                                event.acceleration.x, event.acceleration.y,
                                event.acceleration.z);
                    }
                }
            }

            // Check if we are exiting.
            if (state->destroyRequested != 0) {
                engine_term_display(&engine);
                return;
            }
        }

        if (engine.animating) {
            // Done with events; draw next animation frame.
            engine.state.angle += .01f;
            if (engine.state.angle > 1) {
                engine.state.angle = 0;
            }

            // Drawing is throttled to the screen update rate, so there
            // is no need to do timing here.
            engine_draw_frame(&engine);
        }
    }
}
//END_INCLUDE(all)