由于这个原因，我终于设法构建了libjpeg-turbo静态库 libjpeg-turbo for android 现在我有一个libjpeg.a和一个由ndk-build
生成的libsimd.a但是我无法找到有关下一步该怎么做的任何信息？我正在使用BitmapFactory中的构建从缓冲区（从套接字）解码jpeg到位图
byte[] jpgBits = new byte[jpgBitsLen];
dis.readFully(jpgBits);
Bitmap bmp = BitmapFactory.decodeByteArray(jpgBits, 0, jpgBitsLen);
如何用libjpeg-turbo替换BitmapFactory.decodeByteArray？
我使用此
在我的电脑上编码流tjhandle rmfdJpegCompressor = tjInitCompress();
tjCompress2(rmfdJpegCompressor, (unsigned char *)s_rmfdPixels, MFD_WH, 0, MFD_WH, TJPF_BGRX,
&rmfdBits, &rmfdBitsLen, TJSAMP_420, RMFD_JPEG_QUALITY,
0);
tjDestroy(rmfdJpegCompressor);
哪个工作正常，所以我认为必须有一个Android等价物？
我读过这篇文章 https://wiki.linaro.org/BenjaminGaignard/libjpeg-turboAndSkia 这是否意味着使用它的唯一方法是重建android源码，所以它使用libjpeg-turbo？我读到某处有一个兼容性api和libjpeg-turbo的原生api，我很高兴使用任何api最容易，因为我不喜欢重建android我尝试过以下方法： 在我的项目根目录下，我创建了文件夹jni / include并将turbojpeg.h放在那里 在我的项目根目录下，我创建了文件夹jni / prebuilt并将libjpeg.a放在那里
在我的java代码中，我把
private native int tjInitDecompress();
并在onCreate中添加
int i = tjInitDecompress();
Log.d("MainActivity", "i="+i);
它构建并运行但在tjInitDecompress崩溃
在日志中说： 找不到本机Lcom / example.jpegtest / MainActivity的实现; .tjInitDecompress（）I
感谢
答案 0 :(得分：4)
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。只需a-x0-9就是最好的。
然后我将所有libjpeg-turbo文件和dirs复制到jni并测试ndk-build仍然有用
然后我为这样的libjpg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);
}
重要的是，您必须将com_design2112_fbmslpit_MainActivity重命名为您的包和类才能使其正常工作
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复制到正确的名称并放置
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。你可以任何你想要的方式显示bmp。
这也是我的一大堆工作，以确定根本没有jni ndk经验。如果有人发现这个有用，请给我发一封啤酒。
更新，这是令人震惊的消息，它需要20ms来解码450x450图像。 内置的BitmapFactory.decodeByteArray大致相同！
如果其他人尝试此操作并获得不同的结果，请记下