I am going to load an image by provided file_path and then downsample it then save it. The whole thing should be done on android device.
I am in trouble to load an image on device and convert to halide::buffer.
Halide::Tools::load_image didn't work on android if I use it like
JNIEXPORT bool JNICALL Java_com_example_boxdownsample_MainActivity_downsample(
JNIEnv *env, jobject obj, jstring file_path) { ...
const char *path = env->GetStringUTFChars(file_path, NULL);
std::string work_path = path;
LOGD("the path is:%s", path);
std::string input_file = work_path + "input.png";
std::string output_file = work_path + "output.png";
Halide::Buffer<uint16_t> input = Halide::Tools::load_image(input_file);//load_image didn't work ....
int ret = box_downsample_halide(input, downsample_factor, output_u16); //box_downsample_halide is a static lib generated by halide generator
... } }
So, am I use it wrong? or
I should load it use java(that would be bitmap format) then encode it to halide::buffer, but this seems a bit hard and indirect.
Is there any easier way to do it?
Thanks!
UPDATE:
I found a way, in case who also need this, please go to my github
Related
I'm struggling with reading file stream inside Android environment using C++ library.
I believe I set all the permissions correctly (1st figure) and I'm getting the file path using Android internal library. Would you please give me a snippet to correctly read a file using std::ifstream.getline()?
For instance, I get "/document/1EF7-1509:Download/015_1440.jpg" for the image file existing in the 2nd figure under "Download" folder. This path is a raw value returned by "Intent.getData().getPath()" with "ACTION_GET_CONTENT".
extern "C" JNIEXPORT jstring JNICALL Java_com_example_testpplication_MainActivity_testGeneralEncryption(JNIEnv* env, jobject, jstring myString)
{
const char *nativeString = env->GetStringUTFChars(myString, nullptr);
std::string filePath = std::string(nativeString);
std::string buffer;
std::ifstream fStreamIn(filePath);
if(fStreamIn.is_open())
{
std::getline(fStreamIn, buffer);
}
else
{
bool exists = fStreamIn.good();
if(exists)
{
buffer = "Exists";
}
else
{
buffer = "Non-existing";
}
}
return env->NewStringUTF((buffer + ":" + filePath).c_str());
}
Thanks to #blackapps, I did a google with a different keyword and found below answer. Basically, my question is a duplicate.
Inspired by this answer:
https://stackoverflow.com/a/49221353/1770003
The idea is, Android doesn't directly return the absolute path as other OS reports like Windows. A different approach is needed.
The approach I took is,
Add this in my solution: https://android-arsenal.com/details/1/8142#!package
Edit the project: https://github.com/onimur/handle-path-oz/wiki/Java-Single-Uri
In my case, I moved the caller into onRequestHandPathOz which is add by implementing "HandlePathOzListener.SingleUri".
#Override
public void onRequestHandlePathOz(PathOz pathOz, Throwable throwable)
{
txt_pathShow.setText(testGeneralEncryption(pathOz.getPath()));
}
The method "testGeneralEncryption" is defined in the original question and pathOz.getPath() is passed as an argument to the parameter "jstring myString".
This simple program to write into a file is running fine in my emulator as I am getting a text file generated inside the sdcard(text file has HELLO WORLD in it) along with the given message on emulator screen.
jstring
Java_com_example_hellojni_HelloJni_stringFromJNI( JNIEnv* env,
jobject thiz )
{
FILE* file = fopen("/sdcard/hello.txt","w+");
if (file != NULL)
{
fputs("HELLO WORLD!\n", file);
fflush(file);
fclose(file);
}
return (*env)->NewStringUTF(env, "Hello from JNI (with file io)!");
}
But when I try to read the file using this program I am facing problems. It outputs nothing on the emulator screen or on logcat. As seen from the above program there definitely is no problem with the location of sdcard or with using FILE operations. How to fix it?
JNIEXPORT jstring JNICALL Java_com_example_myproject_MainActivity_doSomething( JNIEnv* env, jobject thiz)
{
// Counts the characters inside file
char ch;
int cnt= 0;
FILE* fptr = fopen("/sdcard/hello.txt","r");
while((ch=fgetc(fptr))!=EOF)
cnt++;
fclose(fptr);
LOGE("cnt: %d",cnt);
return (*env)->NewStringUTF(env, "Hello from JNI (with file io)!");
}
Thanks
EDIT:
This above code to read file works well in linux gcc but has errors working in Android. Changing it as mentioned by Andrew solves it.
fgetc() returns int, not char, so this loop never terminates:
while((ch=fgetc(fptr))!=EOF)
cnt++;
because ch can never equal EOF.
I am trying to use openCV in my android project and trying to run this native code but I don't know how to use this parameter
JNIEXPORT jint JNICALL Java_com_example_helloopencvactivity_nativecalls_filepath
(JNIEnv * env, jobject jo, jstring str1, jstring str2) {
cv::Mat img1 = cv::imread("");
}
I tried using this
const char *nativeString = (*env)->GetStringUTFChars(env, str1, 0);
cv::Mat img1 = cv::imread(nativeString);
but i am getting this error error: no matching function for call to '_JNIEnv::GetStringUTFChars
I need to pass the file path from android file system to openCV's native code for processing, the passing element is string and should be read by imread
first in the java side, my codes looks likeļ¼
private String path="/mnt/sdcard/";
InitFeature(width,height,path);
public native void InitFeature(int width, int height,String path);
then in the jni side, it's:
//passed from the java part and release after InitFreature
const char* nPath;
//to save the globle path
char* g_path;
JNIEXPORT void JNICALL Java_org_opencv_samples_tutorial6_Tutorial2Activity_InitFeature(JNIEnv* env, jobject,jint width,jint height,jstring path);
JNIEXPORT void JNICALL Java_org_opencv_samples_tutorial6_Tutorial2Activity_InitFeature(JNIEnv* env, jobject,jint width,jint height,jstring path)
{
//jsize path_size;
nPath=env->GetStringUTFChars(path,NULL);
//path_size=env->GetArrayLength(path);
LOGD("path: %s \n",nPath);
int length=strlen(nPath);
LOGD("length: %d \n",length);
g_path=new char[length+1];
memcpy(g_path,nPath,length+1);
LOGD("path_2: %s \n",g_path);
LOGD("length: %d \n",strlen(g_path));
char l_path[128];
strcpy(l_path,g_path);
strcat(l_path,"color.jpg");
LOGD("path_3: %s \n",l_path);
LOGD("length: %d \n",sizeof(l_path));
m_width=width;
m_height=height;
center.x=float (m_width/2.0+0.5);//float (Img_tmp->width/2.0+0.5);
center.y=float (m_width/2.0+0.5);//float (Img_tmp->height/2.0+0.5);
env->ReleaseStringUTFChars(path,nPath);
}
since I have different native calls, one to initiate features(shown here) and others to process every frame, and after you env->ReleaseStringUTFChars(path,nPath); the string would be invisible to jni part. I have the copy the string to a global char* g_path;
and a little sample is here as well, the file path is "/mnt/sdcard/color.jpg" and check those logs.
then you can use imread() to get this jpg.
I use other libs like libjpg, so I am not showing the codes here.
Is there a way for my android app to retrieve and set extended user attributes of files? Is there a way to use java.nio.file.Files on android? Is there any way to use setfattr and getfattr from my dalvik app? I know that android use the ext4 file system, so i guess it should be possible. Any suggestions?
The Android Java library and the bionic C library do not support it. So you have to use native code with Linux syscalls for that.
Here is some sample code to get you started, tested on Android 4.2 and Android 4.4.
XAttrNative.java
package com.appfour.example;
import java.io.IOException;
public class XAttrNative {
static {
System.loadLibrary("xattr");
}
public static native void setxattr(String path, String key, String value) throws IOException;
}
xattr.c
#include <string.h>
#include <jni.h>
#include <asm/unistd.h>
#include <errno.h>
void Java_com_appfour_example_XAttrNative_setxattr(JNIEnv* env, jclass clazz,
jstring path, jstring key, jstring value) {
char* pathChars = (*env)->GetStringUTFChars(env, path, NULL);
char* keyChars = (*env)->GetStringUTFChars(env, key, NULL);
char* valueChars = (*env)->GetStringUTFChars(env, value, NULL);
int res = syscall(__NR_setxattr, pathChars, keyChars, valueChars,
strlen(valueChars), 0);
if (res != 0) {
jclass exClass = (*env)->FindClass(env, "java/io/IOException");
(*env)->ThrowNew(env, exClass, strerror(errno));
}
(*env)->ReleaseStringUTFChars(env, path, pathChars);
(*env)->ReleaseStringUTFChars(env, key, keyChars);
(*env)->ReleaseStringUTFChars(env, value, valueChars);
}
This works fine on internal storage but not on (emulated) external storage which uses the sdcardfs filesystem or other kernel functions to disable features not supported by the FAT filesystem such as symlinks and extended attributes. Arguably they do this because external storage can be accessed by connecting the device to a PC and the users expects that copying files back and forth preserves all information.
So this works:
File dataFile = new File(getFilesDir(),"test");
dataFile.createNewFile();
XAttrNative.setxattr(dataFile.getPath(), "user.testkey", "testvalue");
while this throws IOException with the error message: "Operation not supported on transport endpoint":
File externalStorageFile = new File(getExternalFilesDir(null),"test");
externalStorageFile.createNewFile();
XAttrNative.setxattr(externalStorageFile.getPath(), "user.testkey", "testvalue");
I want to know how to get a custom object from Java to c++?
I need to implement a method in c++ for get performance. I already have the method working in java but I want to port to c++.
On Java a I call the method like this:
private native boolean P(Mat Previous, String Name);
On CPP file I need to get the mat object. Getting string is easy! But how can I get the custom mat object similar to c++(cv::Mat)? I need to get java Mat into a cv::Mat.
Here the cpp file:
JNIEXPORT bool JNICALL Java_br_raphael_detector_SimpsonDetector_P
(JNIEnv* env,jobject thiz, jobject Previous, jstring Name){
jboolean sim = false;
const char* N = env->GetStringUTFChars(Name,0);
std::string Nome = N;
//Release
env->ReleaseStringUTFChars(Name,N);
//Then Return
return sim;
}
A java Mat object is a totally different thing from a native cv::Mat, you can't get one directly from the other.
That said, if you know what fields are inside Mat, and you know the corresponding fields in cv::Mat, you can write a conversion function that copies the contents of the fields one-by-one.
// First get the Mat class
jclass Mat = (*env)->GetObjectClass(env, Previous);
// To get a field
jfieldId field = (*env)->GetFieldID(env, Mat, "fieldName", field type);
// To get a method
jmethodId method = (*env)->GetMethodID(env, Mat, "methodName", method signature);
from there you can read the values of fields, or call methods
// getting a field
(*env)->GetObjectField(env, Previous, field);
// calling a method
(*env)->CallObjectMethod(env, Previous, method, parameters);
refer to http://docs.oracle.com/javase/1.5.0/docs/guide/jni/spec/functions.html for details
I'm one year late to the party, but the way you pass a Mat to C is with a jlong with the address of the Java's Mat. You can do something like this:
private static native boolean P(long matAddress, String name);
In C:
JNIEXPORT jboolean JNICALL Java_br_raphael_detector_SimpsonDetector_P
(JNIEnv* env,jobject thiz, jlong matAddress, jstring Name)
{
cv::Mat* image = (cv::Mat*)matAddress;
// Do stuff with image.
}
Then you would call the method in Java like this:
P(myMat.getNativeObjAddr(), name);
OpenCV exposes this method just for cases like this. (I would link to the documentation's page but the website is not loading here, sorry.)