嗯，这是一堆工作，但我终于得到了一些工作，所以我想让任何有兴趣的人知道我是如何做到的。
首先我按照这里的描述构建了 hello-jin 演示
https://developer.android.com/tools/sdk/ndk/index.html
然后我创建了一个新项目，复制了 jni 并更改了 c func 的名称以匹配新的包和类名。不要在你的包名中使用 - 和 _ 否则你会遇到问题。最好只有 a-x0-9。
然后我将所有 libjpeg-turbo 文件和目录复制到 jni 并测试 ndk-build 仍然有效
然后我为这样的 libjpg funs 创建了一个 jni 包装器
tjpegini-arm.c
/*
* Copyright (C) 2009 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*/
#include <jni.h>
#include "turbojpeg.h"
/*
* Class: libjpegturbo_jniapi
* Method: tjInitDecompress
* Signature: ()I
*/
//package com.design2112.fbmslpit
//public class MainActivity
jint JNICALL Java_com_design2112_fbmslpit_MainActivity_tjInitDecompress
(JNIEnv *env, jobject thisObj)
{
return (int)tjInitDecompress();
}
/*
* Class: libjpegturbo_jniapi
* Method: tjDecompressHeader2
* Signature: (I[BI)I
*/
jint JNICALL Java_com_design2112_fbmslpit_MainActivity_tjDecompressHeader2
(JNIEnv *env, jobject thisObj, jint handle, jbyteArray jpegBuf, jint jpegSize)
{
jbyte *real_jpegBuf = (*env)->GetByteArrayElements(env, jpegBuf, 0);
if (!real_jpegBuf) return -1;
//jsize length = (*env)->GetArrayLength(env, real_jpegBuf);
/*for (i = 0; i < length; i++) {
sum += inCArray[i];
}*/
int width, height, jpegSubsamp;
int ret = tjDecompressHeader2((tjhandle)handle,
(unsigned char *)real_jpegBuf, (unsigned long)jpegSize, &width, &height,
&jpegSubsamp);
if(ret!=0) {
return 0;
}
// ok, so pack width and height together
return width<<16 | height;
}
/*
* Class: libjpegturbo_jniapi
* Method: tjDecompress2
* Signature: (I[BI[IIIIII)V
*/
void JNICALL Java_com_design2112_fbmslpit_MainActivity_tjDecompress2
(JNIEnv *env, jobject thisObj, jint handle, jbyteArray jpegBuf, jint jpegSize, jintArray dstBuf,
jint width, jint pitch, jint height, jint pixelFormat, jint flags)
{
jbyte *real_jpegBuf = (*env)->GetByteArrayElements(env, jpegBuf, 0);
if (!real_jpegBuf) return;
jint *real_dstBuf = (*env)->GetIntArrayElements(env, dstBuf, 0);
if (!real_dstBuf) return;
jsize length = (*env)->GetArrayLength(env, jpegBuf);
tjDecompress2((tjhandle)handle,
(unsigned char *)real_jpegBuf, (unsigned long)jpegSize, (unsigned char *)real_dstBuf,
width, pitch, height, pixelFormat, flags);
}
/*
* Class: libjpegturbo_jniapi
* Method: tjDestroy
* Signature: (I)V
*/
void JNICALL Java_com_design2112_fbmslpit_MainActivity_tjDestroy
(JNIEnv *env, jobject thisObj, jint handle)
{
tjDestroy((tjhandle)handle);
}
重要提示，您必须将 com_design2112_fbmslpit_MainActivity 重命名为您的包和类才能正常工作
将 tjpegini-arm.c 添加到 Android.mk makefile 然后在 jni 目录中运行 ndk-build
ndk-build NDK_PROJECT_PATH=. APP_BUILD_SCRIPT=./Android.mk obj/local/armeabi/libjpeg.so LOCAL_ARM_MODE=arm
并将 .so 复制到正确的名称和位置
cp obj/local/armeabi/libjpeg.so ../libs/armeabi/libtjpegjni-arm.so
然后在我的 MainAvtivity.java 中
public class MainActivity extends Activity {
public native int tjInitDecompress();
public native int tjDecompressHeader2(int handle, byte[] jpegBits, int jpegBitsLen);
public native void tjDecompress2(int handle, byte[] jpegBits,
int jpegBitsLen, int[] outbuffer, int width, int pitch, int height,
int pixelFormat, int flags);
public native void tjDestroy(int handle);
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (savedInstanceState == null) {
getFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment())
.commit();
}
File sdcard = Environment.getExternalStorageDirectory();
//Get the text file
File file = new File(sdcard,"/Download/test.jpg");
int jpegBitsLen = (int) file.length();
byte[] jpegBits = new byte[jpegBitsLen];
DataInputStream dis;
try {
dis = new DataInputStream(new FileInputStream(file));
dis.readFully(jpegBits);
dis.close();
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.loadLibrary("tjpegjni-arm");
int jpegDec = tjInitDecompress();
int wh = tjDecompressHeader2(jpegDec, jpegBits, jpegBitsLen);
int width = wh>>16;
int height = wh&0x7fff;
int[] buffer = new int[width*height];
tjDecompress2(jpegDec, jpegBits, jpegBitsLen, buffer, width, 0/*pitch*/, height, 2 /*TJPF_RGBX*/, 0);
tjDestroy(jpegDec);
Bitmap bmp = Bitmap.createBitmap(buffer, width, height, Bitmap.Config.ARGB_8888);
}
基本上就是这样。你可以以任何你想要的方式显示bmp。
这对我来说也是一大堆工作，以弄清楚根本没有 jni ndk 经验。如果有人觉得这很有用，请给我发电子邮件。
更新，这是一个令人震惊的消息，解码 450x450 图像需要 20 毫秒。
内置的 BitmapFactory.decodeByteArray 也差不多！
如果其他人尝试此操作并得到不同的结果，请记下