探讨:如何在NDK中呼叫Java的class

复制代码 代码如下:

package com.clouddevelop.cloudbox;

import android.graphics.Bitmap;

import android.graphics.Canvas;

import android.graphics.Color;

import android.graphics.Paint;

import android.graphics.Paint.FontMetrics;

public class TextManager

{

    public Bitmap create(String text, float size)

    {

        try

        {

            Paint paint = new Paint();

            paint.setColor(Color.WHITE);

            paint.setTextSize(size);

            paint.setAlpha(255);

            paint.setFlags(Paint.ANTI_ALIAS_FLAG);

            paint.setTextAlign(Paint.Align.LEFT);

            paint.setAntiAlias(true);

            float[] widths = new float[text.length()];;

            paint.getTextWidths(text, widths);

            float width = 0;

            for(int i = 0 ;i < widths.length ; i++)

                width += widths[i];

            FontMetrics fm = paint.getFontMetrics();

            int mFontHeight = (int) (Math.ceil(fm.descent - fm.top) + 2);

            Bitmap textImg = Bitmap.createBitmap((int)width, mFontHeight, Bitmap.Config.ARGB_8888);

       编程客栈;     Canvas c = new Canvas(textImg);

            if(fm.ascent < 0)

                c.drawText(text,0,(float)Math.abs(fm.ascent),paint);

            else

                c.drawText(text,0,fm.ascent* -1,paint);

            return textImg;

        }

        catch (Exception e) { }

    &nbhttp://www.devze.comsp;   return null;

    }

    public int getWidth(Bitmap bmp) { return bmp.getWidth(); }

    public int getHeight(Bitmap bmp) { return bmp.getHeight(); }

    public void getPixels(Bitmap bmp, int[] pixels)

    {

        int w = bmp.getWidth();

        int h = bmp.getHeight();

        bmp.getPixels(pixels, 0, w, 0, 0, w, h);

    }

    public void close(Bitmap bmp)

    {

        bmp.recycle();

    }

}

要在NDK中呼叫java的类,第一步当然要有一个Java的类,这个类是我自行建立

要产生一个文字的Bitmap,技术上没什么复杂性,建立Paint,建立Bitmap然后用Canvas将文字写入

在Canhttp://www.devze.comvas的drawText中,会使用FontMetrics的值来写入文字,所以利用fm.ascent让文字往上对齐

复制代码 代码如下:

// declare

JNIEXPORT void JNICALL Java_com_clouddevelop_cloudbox_CloudRenderer_nativeTextInit

(JNIEnv* env, jclass cls, jobject textManager);

// implement

JNIEXPORT void JNICALL Java_com_clouddevelop_cloudbox_CloudRenderer_nativeTextInit

(JNIEnv* env, jclass cls, jobject textManager)

{

    g_env = env;

    g_textmgr = textManager;

    jclass business_class = env->GetObjectClass(g_textmgr);

    AndroidLog("initial textmanager success!");

}

接下来要在JNI中将JNIEnv存到全域变量中g_env

复制代码 代码如下:

jobject getInstance(JNIEnv* env, jclass obj_class)

{

    jmethodID construction_id = env->GetMethodID(obj_class, "<init>", "()V");

    jobject obj = env->NewObject(obj_class, construction_id);

    return obj;

}

GLuint createText(const char* text, float size,float* rWidth, float* rHeight)

{

    if(g_env)

        AndroidLog("g_env exist");

    if(g_textmgr)

        AndroidLog("g_textmgr exist");

    jclass order_class = g_env->FindClass("com/clouddevelop/cloudbox/TextManager");

    AndroidLog("FindClass succeed");

    g_textmgr = getInstance(g_env, order_class);

    jclass cls = g_env->GetObjectClass(g_textmgr);

    AndroidLog("get class succeed");

    jmethohttp://www.devze.comdID mid;

    mid = g_env->GetMethodID(cls, "create",

                             "(Ljava/lang/String;F)Landroid/graphics/Bitmap;");

    AndroidLog("get create succeed");

    jstring data = g_env->NewStringUTF(text);

    jobject textImage = g_env->CallObjectMethod(g_textmgr, mid, data,size);

    AndroidLog("call create succeed");

    g_env->DeleteLocalRef(data);

    g_env->NewGlobalRef(textImage);

    /* Get image dimensions */

    mid = g_env->GetMethodID(cls, "getWidth", "(Landroid/graphics/Bitmap;)I");

    int width = g_env->CallIntMethod(g_textmgr, mid, textImage);

    AndroidLog("call getWidth succeed");

    mid = g_env->GetMethodID(cls, "getHeight", "(Landroid/graphics/Bitmap;)I");

    int height = g_env->CallIntMethod(g_textmgr, mid, textImage);

    AndroidLog("call getHeight succeed");

    *rWidth = width;

    *rHeight = height;

    /* Get pixels */

    jintArray image_data = g_env->NewIntArray(width * height);

    g_env->NewGlobalRef(image_data);

    mid = g_env->GetMethodID(cls, "getPixels", "(Landroid/graphics/Bitmap;[I)V");

    g_env->CallVoidMethod(g_textmgr, mid, textImage, image_data);

 &nbswww.devze.comp;  AndroidLog("call getPixels succeed");

    jint *pixels = g_env->GetIntArrayElements(image_data, 0);

    //Now generate the OpenGL texture object

    GLuint texture;

    glGenTextures(1, &texture);

    glBindTexture(GL_TEXTURE_2D, texture);

    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA,

          GL_UNSIGNED_BYTE, (GLvoid*) pixels);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

    AndroidLog("generate texture succeed");

    g_env->ReleaseIntArrayElements(image_data, pixels, 0);

    g_env->DeleteGlobalRef(image_data);

    /* Free image */

    mid = g_env->GetMethodID(cls, "close", "(Landroid/graphics/Bitmap;)V");

    g_env->CallVoidMethod(g_textmgr, mid, textImage);

    AndroidLog("call close succeed");

    g_env->DeleteGlobalRef(textImage);

    return texture;

}

复制代码 代码如下:

jobject getInstance(JNIEnv* env, jclass obj_class)

{

    jmethodID construction_id = env->GetMethodID(obj_class, "<init>", "()V");

    jobject obj = env->NewObject(obj_class, construction_id);

    return obj;

}

上面这段代码，是在native code中创建一个Java的实开发者_JAVA教程体类

这段代码是我的CloudBox中创建文字纹理的代码

mid = g_env->GetMethodID(cls, "getWidth", "(Landroid/graphics/Bitmap;)I");

int width = g_env->CallIntMethod(g_textmgr, mid, textImage);

其中这两行,GetMethodID先取得该类的方法

在GetMethodID中第一参数是Java 类对象。第二个参数是参数（或方法名），第三个参数是该参数（或方法）的签名。

那要如何取得方法的签名呢？

我们要利用Javap -s TextManager这个指令来做

首先到.class所在的文件夹下，在我的范例中是在D:\CloudAndroid\CloudBox\CloudBoxAndroidGameApplication\bin\com\clouddevelop\cloudbox

然后键入javap -s TextManager就可以得到了,Signature就是我们要的签名。

辛苦了这么久，我的CloudBox终于能显示文字了！！！！！！