[Android NDK]Android JNI开发例子 ---1 静态加载JNI lib

淩亂°似流年 2022-09-18 11:51 228阅读 0赞

JNI函数的注册有两种方法，一种是静态方法，需要用javah为每个声明了native函数的java类编译出的class文件生成一个头文件，另一种是动态注册，通过数据结构保存关联关系实现注册，这里主要介绍静态注册。

1. 创建一个Android Activity 项目， 我的项目有三个Class, 主要是用来显是gl surface view的东西。

package com.example.nativeegl;
    
    import android.opengl.GLSurfaceView;
    import android.os.Bundle;
    import android.app.Activity;
    import android.util.Log;
    import android.view.Menu;
    import android.view.Window;
    import android.view.WindowManager;
    
    public class MainActivity extends Activity {
        GLSurfaceView mGLView;
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            this.requestWindowFeature(Window.FEATURE_NO_TITLE); 
            getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
                    WindowManager.LayoutParams.FLAG_FULLSCREEN); // (NEW)
    
            mGLView = new MyGLSurfaceView(this);
            
            setContentView(mGLView);
        }
    }

GLSurfaceView在有touch事件时更新颜色。

package com.example.nativeegl;
    
    import android.opengl.GLSurfaceView;
    import android.os.Bundle;
    import android.app.Activity;
    import android.content.Context;
    import android.view.Menu;
    import android.view.MotionEvent;
    import android.view.SurfaceHolder;
    
    public class MyGLSurfaceView extends GLSurfaceView {
    
        GLSurfaceView.Renderer mRenderer;
        /**
         * TODO Put here a description of what this constructor does.
         *
         * @param context
         */
        public MyGLSurfaceView(Context context) {
            super(context);
            // TODO Auto-generated constructor stub.
            mRenderer = new MyRenderer();
         // Set the Renderer for drawing on the GLSurfaceView
            setRenderer(mRenderer);
        }
        @Override
        public boolean onTouchEvent(final MotionEvent event) {
            // TODO Auto-generated method stub.
            queueEvent(new Runnable() {  
                public void run() {  
                    ((MyRenderer)mRenderer).setColor(event.getX() / getWidth(), event.getY() / getHeight(), 1.0f);  
                }
            });  
            return true;
        }
    }

Renderer

public class MyRenderer implements GLSurfaceView.Renderer {
    
        private static final String TAG = "bbaiagl";
        private float _red = 0.9f;
        private float _green = 0.2f;
        private float _blue = 0.2f;
       
    //加载库文件
        static {
            System.loadLibrary("myegl_jni");
        }
    //声明native方法，返回String
        public native String nativeGetHelloString();
        
        @Override
        public void onDrawFrame(GL10 gl) {
           // onNativeDrawFrame();
    //使用native方法
     Log.d(TAG, "onDrawFrame "+ nativeGetHelloString());
            // define the color we want to be displayed as the "clipping wall"
            gl.glClearColor(_red, _green, _blue, 1.0f);
            // clear the color buffer to show the ClearColor we called above...
            gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT);
        }
    
        @Override
        public void onSurfaceChanged(GL10 gl, int width, int height) {
            //onNativeSurfaceChanged(width,height);
            Log.d(TAG, "onSurfaceChanged");
            // Sets the current view port to the new size.
            gl.glViewport(0, 0, width, height);// OpenGL docs.
    
            // Select the projection matrix
            gl.glMatrixMode(GL10.GL_PROJECTION);// OpenGL docs.
    
            // Reset the projection matrix
            gl.glLoadIdentity();// OpenGL docs.]
            //gl.glOrthof(0, width,0,height,0,10);
            // Calculate the aspect ratio of the window
            GLU.gluPerspective(gl, 45.0f, (float) width / (float) height, 0.1f, 100.0f);
    
            // Select the modelview matrix
            gl.glMatrixMode(GL10.GL_MODELVIEW);// OpenGL docs.
    
            // Reset the modelview matrix
            gl.glLoadIdentity();// OpenGL docs.
        }
    
        @Override
        public void onSurfaceCreated(GL10 gl, EGLConfig config) {
            //onNativeSurfaceCreated();
            Log.d(TAG, "onSurfaceCreate");
            // Set the background color to black ( rgba ).
            gl.glClearColor(0.0f, 0.0f, 0.0f, 0.5f); // OpenGL docs.
    
            // Enable Smooth Shading, default not really needed.
            gl.glShadeModel(GL10.GL_SMOOTH);// OpenGL docs.
    
            // Depth buffer setup.
            gl.glClearDepthf(1.0f);// OpenGL docs.
    
            // Enables depth testing.
            gl.glEnable(GL10.GL_DEPTH_TEST);// OpenGL docs.
    
            // The type of depth testing to do.
            gl.glDepthFunc(GL10.GL_LEQUAL);// OpenGL docs.
    
            // Really nice perspective calculations.
            gl.glHint(GL10.GL_PERSPECTIVE_CORRECTION_HINT, GL10.GL_NICEST);
        }
    
        public void setColor(float r, float g, float b) {
            _red = r;
            _green = g;
            _blue = b;
        }
    }

2. 在项目路径下执行会在项目目录下生成jni文件夹和头文件

javah -classpath bin/classes -d jni com.example.nativeegl.MyRenderer

最后面的参数是 包名.需要native库的类名。  
  
  
3. 根据头文件做cpp文件。

com\_example\_nativeegl\_MyRenderer.h

可以看到自动生成的函数

Java\_com\_example\_nativeegl\_MyRenderer\_nativeGetHelloStrin

Java\_ + 包名+类名+接口名：必须按照这个规则来定义JNI接口的函数名

#include <jni.h>
    /* Header for class com_example_nativeegl_MyRenderer */
    #include <string.h>
    //因为我们的实现是用cpp,而不是c, 所以要定义__cplusplus宏。
    #define __cplusplus
    
    #ifndef _Included_com_example_nativeegl_MyRenderer //这个宏在cpp实现中要删除。 如果不删除的话，当cpp文件包含这个头文件时，因为这个宏在头文件中已经被定义过，所以会导致cpp里面的内容不执行。作用是防止该头文件被重复引用
    #define _Included_com_example_nativeegl_MyRenderer
    
    #ifdef __cplusplus
    extern "C" {
    #endif
    /*
     * Class:     com_example_nativeegl_MyRenderer
     * Method:    nativeGetHelloString
     * Signature: ()Ljava/lang/String;
     */
    JNIEXPORT jstring JNICALL Java_com_example_nativeegl_MyRenderer_nativeGetHelloString
      (JNIEnv *, jobject);
    
    #ifdef __cplusplus
    }
    #endif
    #endif

在jni文件夹下，

mkdir include
    mv a.h include/
    cp include/a.h a.cpp

在头文件的基础上修改成cpp

#include "com_example_nativeegl_MyRenderer.h" //添加头文件
    extern "C" {
    /*
     * Class:     com_example_nativeegl_MyRenderer
     * Method:    nativeGetHelloString
     * Signature: ()Ljava/lang/String;
     */
    JNIEXPORT jstring JNICALL Java_com_example_nativeegl_MyRenderer_nativeGetHelloString
      (JNIEnv *env, jobject obj) {
          return env->NewStringUTF((char*)" This is calling from JNI suckers!");
      }
    }

添加Android.mk文件。Android.mk的语法，请查看[链接][Link 1]

LOCAL_PATH := $(call my-dir)
    include $(CLEAR_VARS)
    LOCAL_CFLAGS    := -Wall    //gcc编译的参数。 man gcc 查询
    LOCAL_MODULE    := myegl_jni
    LOCAL_C_INCLUDES :=$(LOCAL_PATH)/include
    LOCAL_CPP_EXTENSION := .cpp
    LOCAL_SRC_FILES := com_example_nativeegl_MyRenderer.cpp
    
    include $(BUILD_SHARED_LIBRARY)

在项目的根目录执行

ndk-build

编译出动态库。

[Link 1]: http://blog.csdn.net/virus026/article/details/16840853