呼叫Java_探讨:如何在NDK中呼叫Java的class

废话不多说,直接上码.......

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);

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) { }

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Canvas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

// 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

jobject getInstance(JNIEnv* env, jclass obj_class)

{

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

jmethodID 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);

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;

}

jobject getInstance(JNIEnv* env, jclass obj_class)

{

jmethodID construction_id = env->GetMethodID(obj_class, "", "()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！！！！！！