Android JNI之cocos2D源码分析

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Cocos2d 做为一个跨平台的游戏引擎，对于Android中java与C的互相调用很有借鉴意义。本文只分析一下Cocos2d JNI 部分的封装代码。

代码结构

关于多平台的主要目录
  • cocos 主要源码
    • platform 支持不同平台的项目源码
      • android
      • ios
      • …
  • external cocos依赖的一些第三方开源工具，比如openssl、freetype 等

C++ 调用 java

cocos2d-x引擎对jni的操作进行了封装，提供了一个非常好用的类:JniHelper，定义了一些常用的接口

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 typedef std::unordered_map<JNIEnv*, std::vector<jobject>> LocalRefMapType;

 static void setJavaVM(JavaVM *javaVM);
 static JavaVM* getJavaVM();
 static JNIEnv* getEnv();
 static jobject getActivity();

 static bool setClassLoaderFrom(jobject activityInstance);
 static bool getStaticMethodInfo(JniMethodInfo &methodinfo,
                                 const char *className,
                                 const char *methodName,
                                 const char *paramCode);
 static bool getMethodInfo(JniMethodInfo &methodinfo,
                             const char *className,
                             const char *methodName,
                             const char *paramCode);

 //转换java 字符串为C++字符串
 static std::string jstring2string(jstring str);

 static jmethodID loadclassMethod_methodID;
 static jobject classloader;
 static std::function<void()> classloaderCallback;

 /**
 调用java 无返回值的静态函数
 @brief Call of Java static void method
 @if no such method will log error
 */
 template <typename... Ts>
 static void callStaticVoidMethod(const std::string& className, 
                                  const std::string& methodName, 
                                  Ts... xs) {
     cocos2d::JniMethodInfo t;
     std::string signature = "(" + std::string(getJNISignature(xs...)) + ")V";
     if (cocos2d::JniHelper::getStaticMethodInfo(t, className.c_str(), methodName.c_str(), signature.c_str())) {
         LocalRefMapType localRefs;
         t.env->CallStaticVoidMethod(t.classID, t.methodID, convert(localRefs, t, xs)...);
         t.env->DeleteLocalRef(t.classID);
         deleteLocalRefs(t.env, localRefs);
     } else {
         reportError(className, methodName, signature);
     }
 }
 /**========================================
     还有很多类似的静态函数调用
     callStaticBooleanMethod、callStaticIntMethod 。。。
 
     template <typename... Ts> 类似于java中的泛型

     通过 template <typename... Ts> 和 getJNISignature 根据实参自动拼接出调用java函数需要的参数类型字符串
 ========================================*/

 static std::string getJNISignature() {
     return "";
 }

 static std::string getJNISignature(bool) {
     return "Z";
 }

 static std::string getJNISignature(char) {
     return "C";
 }

 static std::string getJNISignature(short) {
     return "S";
 }

 static std::string getJNISignature(int) {
     return "I";
 }

 static std::string getJNISignature(long) {
     return "J";
 }

 static std::string getJNISignature(float) {
     return "F";
 }

static  std::string getJNISignature(double) {
     return "D";
 }

 static std::string getJNISignature(const char*) {
     return "Ljava/lang/String;";
 }

 static std::string getJNISignature(const std::string&) {
     return "Ljava/lang/String;";
 }

 template <typename T>
 static std::string getJNISignature(T x) {
     // This template should never be instantiated
     static_assert(sizeof(x) == 0, "Unsupported argument type");
     return "";
 }

 template <typename T, typename... Ts>
 static std::string getJNISignature(T x, Ts... xs) {
     return getJNISignature(x) + getJNISignature(xs...);
 }

java 调用C++函数

看过java JNI 的同学应该都了解过了。这里只简单说一下大概流程不做详细赘述了。

  1. 首先我们会在java 类中定义native函数
    private static native void nativeTouchesBegin(final int id, final float x, final float y);
  2. 然后我们在c++ 中定义对应的实现函数。需要注意的是java 类型和C类型的转换。下面展示一下cocos 对触摸事件的封装。凑字数了哈哈。
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// TouchesJni.cpp

#include "base/CCDirector.h"
#include "base/CCEventKeyboard.h"
#include "base/CCEventDispatcher.h"
#include "platform/android/CCGLViewImpl-android.h"

#include <android/log.h>
#include <jni.h>

using namespace cocos2d;

extern "C" {
    JNIEXPORT void JNICALL Java_org_cocos2dx_lib_Cocos2dxRenderer_nativeTouchesBegin(JNIEnv * env, jobject thiz, jint id, jfloat x, jfloat y) {
        intptr_t idlong = id;
        cocos2d::Director::getInstance()->getOpenGLView()->handleTouchesBegin(1, &idlong, &x, &y);
    }

    JNIEXPORT void JNICALL Java_org_cocos2dx_lib_Cocos2dxRenderer_nativeTouchesEnd(JNIEnv * env, jobject thiz, jint id, jfloat x, jfloat y) {
        intptr_t idlong = id;
        cocos2d::Director::getInstance()->getOpenGLView()->handleTouchesEnd(1, &idlong, &x, &y);
    }

    JNIEXPORT void JNICALL Java_org_cocos2dx_lib_Cocos2dxRenderer_nativeTouchesMove(JNIEnv * env, jobject thiz, jintArray ids, jfloatArray xs, jfloatArray ys) {
        int size = env->GetArrayLength(ids);
        jint id[size];
        jfloat x[size];
        jfloat y[size];

        env->GetIntArrayRegion(ids, 0, size, id);
        env->GetFloatArrayRegion(xs, 0, size, x);
        env->GetFloatArrayRegion(ys, 0, size, y);

        intptr_t idlong[size];
        for(int i = 0; i < size; i++)
            idlong[i] = id[i];

        cocos2d::Director::getInstance()->getOpenGLView()->handleTouchesMove(size, idlong, x, y);
    }

    JNIEXPORT void JNICALL Java_org_cocos2dx_lib_Cocos2dxRenderer_nativeTouchesCancel(JNIEnv * env, jobject thiz, jintArray ids, jfloatArray xs, jfloatArray ys) {
        int size = env->GetArrayLength(ids);
        jint id[size];
        jfloat x[size];
        jfloat y[size];

        env->GetIntArrayRegion(ids, 0, size, id);
        env->GetFloatArrayRegion(xs, 0, size, x);
        env->GetFloatArrayRegion(ys, 0, size, y);

        intptr_t idlong[size];
        for(int i = 0; i < size; i++)
            idlong[i] = id[i];

        cocos2d::Director::getInstance()->getOpenGLView()->handleTouchesCancel(size, idlong, x, y);
    }

#define KEYCODE_BACK 0x04
#define KEYCODE_MENU 0x52
#define KEYCODE_DPAD_UP 0x13
#define KEYCODE_DPAD_DOWN 0x14
#define KEYCODE_DPAD_LEFT 0x15
#define KEYCODE_DPAD_RIGHT 0x16
#define KEYCODE_ENTER 0x42
#define KEYCODE_PLAY  0x7e
#define KEYCODE_DPAD_CENTER  0x17
    
    
    static std::unordered_map<int, cocos2d::EventKeyboard::KeyCode> g_keyCodeMap = {
        { KEYCODE_BACK , cocos2d::EventKeyboard::KeyCode::KEY_ESCAPE},
        { KEYCODE_MENU , cocos2d::EventKeyboard::KeyCode::KEY_MENU},
        { KEYCODE_DPAD_UP  , cocos2d::EventKeyboard::KeyCode::KEY_DPAD_UP },
        { KEYCODE_DPAD_DOWN , cocos2d::EventKeyboard::KeyCode::KEY_DPAD_DOWN },
        { KEYCODE_DPAD_LEFT , cocos2d::EventKeyboard::KeyCode::KEY_DPAD_LEFT },
        { KEYCODE_DPAD_RIGHT , cocos2d::EventKeyboard::KeyCode::KEY_DPAD_RIGHT },
        { KEYCODE_ENTER  , cocos2d::EventKeyboard::KeyCode::KEY_ENTER},
        { KEYCODE_PLAY  , cocos2d::EventKeyboard::KeyCode::KEY_PLAY},
        { KEYCODE_DPAD_CENTER  , cocos2d::EventKeyboard::KeyCode::KEY_DPAD_CENTER},
        
    };
    
    JNIEXPORT jboolean JNICALL Java_org_cocos2dx_lib_Cocos2dxRenderer_nativeKeyEvent(JNIEnv * env, jobject thiz, jint keyCode, jboolean isPressed) {
        Director* pDirector = Director::getInstance();
        
        auto iterKeyCode = g_keyCodeMap.find(keyCode);
        if (iterKeyCode == g_keyCodeMap.end()) {
            return JNI_FALSE;
        }
        
        cocos2d::EventKeyboard::KeyCode cocos2dKey = g_keyCodeMap.at(keyCode);
        cocos2d::EventKeyboard event(cocos2dKey, isPressed);
        cocos2d::Director::getInstance()->getEventDispatcher()->dispatchEvent(&event);
        return JNI_TRUE;
        
    }}