If you don't have time to read or if you know the information, the final code for getting a full-size image from an Android smartphone camera is located at the end of the article.
Description of the problem
If you are writing a cross-platform application, you can use the QCamera class to get an image from a PC camera , an example for which is described in the Qt documentation.
According to the above example, we add to the .pro file
QT += multimedia multimediawidgets
Next, we create a widget in our program that displays an image from a webcam and saves it in a QPixmap or QImage for future use.
When the task arises to do the same on Android, it turns out that multimediawidgets are not supported by this OS and the camera will take and save pictures, but what it displays at the moment will be a mystery, since QCameraViewfinder uses multimediawidgets and does not display on Android nothing. Further search for a solution to the problem leads to two solutions:
use QML and write your own Qt Quick-element that performs this function, then dock it with the rest of the application in Qt Widgets , C ++;
use the default Android smartphone application to receive a photo, then process it in your application.
Consider the first option
If you are a C ++ programmer of Qt Widgets , then the next episodic deepening into QML will take you time, add to this time to write a Qt Quick-element , dock this element with C ++ code, debug the written code. If you are not a professional in QML it turns out to be long and difficult.
Consider the second option
Android- -, , , Java- (JNI — Java Native Interface) ++ QtAndroid. . , , , Android .
, Android- .
Android , . , GitHub , . , , FileUriExposedException , .
, , , Java- — .
.pro .
Android.
android {
QT +=androidextras
}
, QAndroidActivityResultReceiver. , , Qt, QObject.
(.h) :
#ifndef CAMSHOT_H
#define CAMSHOT_H
#include <QObject>
#include <QString>
#include <cstring>
#include <QImage>
#include <QDebug>
#include <QtAndroid>
#include <QAndroidActivityResultReceiver>
#include <QAndroidParcel>
class CamShot : public QObject, public QAndroidActivityResultReceiver
{
Q_OBJECT
public:
CamShot(QObject *parent = nullptr):QObject(parent),QAndroidActivityResultReceiver(){}
static const int RESULT_OK = -1;
static const int REQUEST_IMAGE_CAPTURE = 1;
static const int REQUEST_TAKE_PHOTO = REQUEST_IMAGE_CAPTURE;
void handleActivityResult(int receiverRequestCode, int resultCode, const QAndroidJniObject &data) override;
static QImage camThumbnailToQImage(const QAndroidJniObject &data);
public slots:
void aMakeShot();
signals:
void createNew(const QImage &img);
};
#endif // CAMSHOT_H
(.cpp) :
QImage CamShot::camThumbnailToQImage(const QAndroidJniObject &data){
QAndroidJniObject bundle = data.callObjectMethod("getExtras","()Landroid/os/Bundle;");
qDebug()<<"bundle.isValid() "<<bundle.isValid()<<bundle.toString();
QAndroidJniObject bundleKey = QAndroidJniObject::fromString("data");
const QAndroidJniObject aBitmap (data.callObjectMethod("getParcelableExtra", "(Ljava/lang/String;)Landroid/os/Parcelable;", bundleKey.object<jstring>()));
qDebug()<<"aBitmap.isValid() "<<aBitmap.isValid()<<aBitmap.toString();
jint aBitmapWidth = aBitmap.callMethod<jint>("getWidth");
jint aBitmapHeight = aBitmap.callMethod<jint>("getHeight");
QAndroidJniEnvironment env;
const int32_t aBitmapPixelsCount = aBitmapWidth * aBitmapHeight;
jintArray pixels = env->NewIntArray(aBitmapPixelsCount);
jint aBitmapOffset = 0;
jint aBitmapStride = aBitmapWidth;
jint aBitmapX = 0;
jint aBitmapY = 0;
aBitmap.callMethod<void>("getPixels","([IIIIIII)V", pixels, aBitmapOffset, aBitmapStride, aBitmapX, aBitmapY, aBitmapWidth, aBitmapHeight);
jint *pPixels = env->GetIntArrayElements(pixels, nullptr);
QImage img(aBitmapWidth, aBitmapHeight, QImage::Format_ARGB32);
int lineSzB = aBitmapWidth * sizeof(jint);
for (int i = 0; i < aBitmapHeight; ++i){
uchar *pDst = img.scanLine(i);
const uchar *pSrc = reinterpret_cast<const uchar*>(pPixels + aBitmapWidth * i + aBitmapWidth);
memcpy(pDst, pSrc, lineSzB);
}
env->DeleteLocalRef(pixels); //env->ReleaseIntArrayElements(pixels, pPixels, 0); , , DeleteLocalRef.
return img;
}
void CamShot::aMakeShot() {
QAndroidJniObject action = QandroidJniObject::fromString("android.media.action.IMAGE_CAPTURE");
// Java- ( ), (- "/"), "android/content/Intent", "java/lang/String".
// Java-, "L" ";" , "Landroid/content/Intent ;", "Ljava/lang/String;".
// , , "V" (void) "[IIIIIII" ( jint, 6 jint )
//, :
QAndroidJniObject intent=QAndroidJniObject("android/content/Intent","(Ljava/lang/String;)V", action.object<jstring>());
QtAndroid::startActivity(intent, REQUEST_IMAGE_CAPTURE, this);
}
void CamShot::handleActivityResult(int receiverRequestCode, int resultCode, const QAndroidJniObject &data){
if ( receiverRequestCode == REQUEST_IMAGE_CAPTURE && resultCode == RESULT_OK )
{
const QImage thumbnail (camThumbnailToQImage(data));
if (!thumbnail.isNull())
emit createNew(thumbnail);
}
}
JNI-
Java- ( Java-), (- "/"), "android/content/Intent", "java/lang/String";
Java-, "L" ";" , "Landroid/content/Intent;", "Ljava/lang/String;";
, ( ), "V" (void), "I" (jint) "[IIIIIII" ( jint, 6 jint );
:
C/C++
JNI
Java
Signature
uint8_t/unsigned char
jboolean
bool
Z
int8_t/char/signed char
jbyte
byte
B
uint16_t/unsigned short
jchar
char
C
int16_t/short
jshort
short
S
int32_t/int/(long)
jint
int
I
int64_t/(long)/long long
jlong
long
J
float
jfloat
float
F
double
jdouble
double
D
void
void
V
:
JNI
Java
Signature
jbooleanArray
bool[]
[Z
jbyteArray
byte[]
[B
jcharArray
char[]
[C
jshortArray
short[]
[S
jintArray
int[]
[I
jlongArray
long[]
[L
jfloatArray
float[]
[F
jdoubleArray
double[]
[D
jarray
type[]
[Lfully/qualified/type/name;
jarray
String[]
[Ljava/lang/String;
, JNI- QAndroidJniEnvironment, : NewIntArray, GetIntArrayElements, DeleteLocalRef GetArrayLength,GetObjectArrayElement, SetObjectArrayElement, ..
(pdf) Practical Qt on Android JNI — qtcon.
class CamShot :
, Android ( Java-);
void handleActivityResult(int receiverRequestCode, int resultCode, const QAndroidJniObject &data) override;
Java- Intent ;
static QImage camThumbnailToQImage(const QAndroidJniObject &data);
Java- Intent Java- Bitmap, (32- ) QImage;
void aMakeShot();
;
void createNew(const QImage &img);
.
void aMakeShot() Java- Intent , , — . (Intent) (Activity).
- . , handleActivityResult, : . , camThumbnailToQImage QImage Java- Bitmap Qt.
static QImage camThumbnailToQImage(const QAndroidJniObject &data) override;
Java- Intent Java- Bundle, Intent:
Bundle getExtras()
Bundle <->:<>. Android , . "data".
Java- Bitmap , Intent:
T getParcelableExtra (String name)
C Bitmap QImage , . . Bitmap . ( ) QImage .
Bitmap QImage Bitmap:
void getPixels (int[] pixels, int offset, int stride, int x, int y, int width, int height)
jintArray pixels = env->NewIntArray(aBitmapPixelsCount);
, , , C++ :
jint *pPixels = env->GetIntArrayElements(pixels, nullptr);
Qimage. ,
env->DeleteLocalRef(pixels);
QImage.
. .
FileProvider, Uri . , Android, , :
androidx.core.content.FileProvider;
android.support.v4.content.FileProvider.
— , Qt, QtCreator:
()→ «» → «» → «»→ «Android»→ «SDK Manager»→ «» → «Extras»→ «Android Support Repository» - «» .
Android
QtCreator «». « »→ «». «Build Android APK» → «Create Templates». « Gradle Android», «»:
«android», .
Android
- Android, .pro android: :
android { QT +=androidextras } # … DISTFILES += \ android: android/AndroidManifest.xml \ android: android/build.gradle \ android: android/gradle/wrapper/gradle-wrapper.jar \ android: android/gradle/wrapper/gradle-wrapper.properties \ android: android/gradlew \ android: android/gradlew.bat \ android: android/res/values/libs.xml \ todo.txt
AndroidManifest.xml
«AndroidManifest.xml» android/AndroidManifest.xml,
</activity>
<!-- For adding service(s) please check: https://wiki.qt.io/AndroidServices ->
:
<provider android:name="android.support.v4.content.FileProvider" android:authorities="org.qtproject.example.qsketch.fileprovider" android:grantUriPermissions="true" android:exported="false">
<meta-data android:name="android.support.FILE_PROVIDER_PATHS" android:resource="@xml/file_paths"/>
</provider>
, - .
, «AndroidManifest.xml» «res» «values», «xml», «file_paths.xml» (… /abin/AndroidManifest.xml) (… /abin/res/xml/file_paths.xml). :
<?xml version="1.0" encoding="utf-8"?>
<paths xmlns:android="http://schemas.android.com/apk/res/android">
<external-files-path name="shared" path="shared/" />
</paths>
shared/
, FileProvider
android/build.gradle, dependencies :
compile'com.android.support:support-v4:25.3.1'
:
dependencies { implementation fileTree(dir: 'libs', include: ['*.jar', '*.aar']) compile'com.android.support:support-v4:25.3.1' }
, Android Support Repository.
Sharing Files on Android or iOS from or with your Qt App - Part 4 .
(.h) :
#ifndef CAMSHOT_H
#define CAMSHOT_H
#include <QObject>
#include <QImage>
#include <QString>
#include <QDebug>
#include <QtAndroid>
#include <QAndroidActivityResultReceiver>
#include <QAndroidParcel>
#include "auxfunc.h"
class CamShot : public QObject, public QAndroidActivityResultReceiver
{
Q_OBJECT
public:
static const int RESULT_OK = -1;
static const int REQUEST_IMAGE_CAPTURE = 1;
static const int REQUEST_TAKE_PHOTO = REQUEST_IMAGE_CAPTURE;
enum ImgOrientation {ORIENTATION_UNDEFINED = 0, ORIENTATION_NORMAL = 1, ORIENTATION_FLIP_HORIZONTAL = 2, ORIENTATION_ROTATE_180 = 3, ORIENTATION_FLIP_VERTICAL = 4, ORIENTATION_TRANSPOSE = 5,
ORIENTATION_ROTATE_90 = 6, ORIENTATION_TRANSVERSE = 7, ORIENTATION_ROTATE_270 = 8};
void handleActivityResult(int receiverRequestCode, int resultCode, const QAndroidJniObject &data) override;
static QImage aBitmapToQImage(const QAndroidJniObject &aBitmap);
static QImage camThumbnailToQImage(const QAndroidJniObject &data);
ImgOrientation needRotateAtRightAngle();
QImage camImageToQImage();
static void applyOrientation(QImage &img, const ImgOrientation &orientation);
explicit CamShot(QObject *parent = nullptr):QObject(parent),QAndroidActivityResultReceiver(){}
~CamShot();
private:
QAndroidJniObject tempImgURI;
QAndroidJniObject tempImgFile;
QAndroidJniObject tempImgAbsPath;
bool _thumbnailNotFullScaleRequested;
public slots:
void aMakeShot(const bool &thumbnailNotFullScale = false);
signals:
void createNew(const QImage &img);
};
#endif // CAMSHOT_H
(.cpp) :
QImage CamShot::aBitmapToQImage(const QAndroidJniObject &aBitmap){
if (!aBitmap.isValid())
return QImage();
jint aBitmapWidth = aBitmap.callMethod<jint>("getWidth");
jint aBitmapHeight = aBitmap.callMethod<jint>("getHeight");
QAndroidJniEnvironment env;
const int32_t aBitmapPixelsCount = aBitmapWidth * aBitmapHeight;
jintArray pixels = env->NewIntArray(aBitmapPixelsCount);
jint aBitmapOffset = 0;
jint aBitmapStride = aBitmapWidth;
jint aBitmapX = 0;
jint aBitmapY = 0;
aBitmap.callMethod<void>("getPixels","([IIIIIII)V", pixels, aBitmapOffset, aBitmapStride, aBitmapX, aBitmapY, aBitmapWidth, aBitmapHeight);
jint *pPixels = env->GetIntArrayElements(pixels, nullptr);
QImage img(aBitmapWidth, aBitmapHeight, QImage::Format_ARGB32);
int lineSzB = aBitmapWidth * sizeof(jint);
for (int i = 0; i < aBitmapHeight; ++i){
uchar *pDst = img.scanLine(i);
const uchar *pSrc = reinterpret_cast<const uchar*>(pPixels + aBitmapWidth * i + aBitmapWidth);
memcpy(pDst, pSrc, lineSzB);
}
env->DeleteLocalRef(pixels); //env->ReleaseIntArrayElements(pixels, pPixels, 0); , , DeleteLocalRef.
return img;
}
QImage CamShot::camThumbnailToQImage(const QAndroidJniObject &data){
//
QAndroidJniObject bundle = data.callObjectMethod("getExtras","()Landroid/os/Bundle;");
qDebug()<<"bundle.isValid() "<<bundle.isValid()<<bundle.toString();
// jstring ( Java) "data" - <, > - Bitmap (Java)
QAndroidJniObject bundleKey = QAndroidJniObject::fromString("data");
// "data" : Bitmap
const QAndroidJniObject aBitmap (data.callObjectMethod("getParcelableExtra", "(Ljava/lang/String;)Landroid/os/Parcelable;", bundleKey.object<jstring>()));
qDebug()<<"aBitmap.isValid() "<<aBitmap.isValid()<<aBitmap.toString();
return aBitmapToQImage(aBitmap);
}
QImage CamShot::camImageToQImage(){
QAndroidJniObject bitmap = QAndroidJniObject::callStaticObjectMethod("android/graphics/BitmapFactory","decodeFile","(Ljava/lang/String;)Landroid/graphics/Bitmap;",tempImgAbsPath.object<jobject>());
qDebug()<<"bitmap.isValid() "<<bitmap.isValid()<<bitmap.toString();
QImage img = aBitmapToQImage(bitmap);
//
if (tempImgFile.isValid())
tempImgFile.callMethod<jboolean>("delete");
return img;
}
CamShot::ImgOrientation CamShot::needRotateAtRightAngle(){
//
QAndroidJniObject exifInterface = QAndroidJniObject("android/media/ExifInterface","(Ljava/lang/String;)V",
tempImgAbsPath.object<jstring>());
qDebug() << __FUNCTION__ << "exifInterface.isValid()=" << exifInterface.isValid();
QAndroidJniObject TAG_ORIENTATION = QAndroidJniObject::getStaticObjectField<jstring>("android/media/ExifInterface", "TAG_ORIENTATION");
qDebug() << __FUNCTION__ << "TAG_ORIENTATION.isValid()=" << TAG_ORIENTATION.isValid()<<TAG_ORIENTATION.toString();
const jint orientation = exifInterface.callMethod<jint>("getAttributeInt","(Ljava/lang/String;I)I",TAG_ORIENTATION.object<jstring>(),static_cast<jint>(ORIENTATION_UNDEFINED));
return static_cast<ImgOrientation>(orientation);
}
void CamShot::applyOrientation(QImage &img, const ImgOrientation &orientation){
switch (orientation){
case ORIENTATION_UNDEFINED:
case ORIENTATION_NORMAL:
break;
case ORIENTATION_FLIP_HORIZONTAL:{
img = img.mirrored(true, false);
break;
}
case ORIENTATION_ROTATE_180:
Aux::rotateImgCW180(img);
break;
case ORIENTATION_FLIP_VERTICAL:{
img = img.mirrored(false, true);
break;
}
case ORIENTATION_TRANSPOSE:{
img = img.mirrored(true, false);
Aux::rotateImgCW270(img);
break;
}
case ORIENTATION_ROTATE_90:
Aux::rotateImgCW90(img);
break;
case ORIENTATION_TRANSVERSE:{
img = img.mirrored(true, false);
Aux::rotateImgCW90(img);
break;
}
break;
case ORIENTATION_ROTATE_270:
Aux::rotateImgCW270(img);
break;
}
}
void CamShot::handleActivityResult(int receiverRequestCode, int resultCode, const QAndroidJniObject &data){
if ( receiverRequestCode == REQUEST_IMAGE_CAPTURE && resultCode == RESULT_OK )
{
if (_thumbnailNotFullScaleRequested){
const QImage thumbnail (camThumbnailToQImage(data));
if (!thumbnail.isNull())
emit createNew(thumbnail);
return;
}
const ImgOrientation orientation = needRotateAtRightAngle();
QImage image (camImageToQImage());
if (!image.isNull()){
applyOrientation(image, orientation);
emit createNew(image);
}
}
}
void CamShot::aMakeShot(const bool &thumbnailNotFullScale) {
QAndroidJniObject action = QAndroidJniObject::fromString("android.media.action.IMAGE_CAPTURE");
//
QAndroidJniObject intent=QAndroidJniObject("android/content/Intent","(Ljava/lang/String;)V",
action.object<jstring>());
qDebug() << __FUNCTION__ << "intent.isValid()=" << intent.isValid();
_thumbnailNotFullScaleRequested = thumbnailNotFullScale;
if (thumbnailNotFullScale) {
//
QtAndroid::startActivity(intent, REQUEST_IMAGE_CAPTURE, this);
return;
}
//
QAndroidJniObject context = QtAndroid::androidContext();
QString contextStr (context.toString());
qDebug() <<"Context: "<<contextStr;
//
QAndroidJniObject extDir = context.callObjectMethod("getExternalFilesDir", "(Ljava/lang/String;)Ljava/io/File;", NULL);
qDebug() << __FUNCTION__ << "extDir.isValid()=" << extDir.isValid()<<extDir.toString();
//
QAndroidJniObject extDirAbsPath = extDir.callObjectMethod("getAbsolutePath","()Ljava/lang/String;");
// . . /res/xml/file_paths.xml
extDirAbsPath = QAndroidJniObject::fromString(extDirAbsPath.toString() + "/shared");
const QString extDirAbsPathStr = extDirAbsPath.toString();
qDebug() << __FUNCTION__ << "extDirAbsPath.isValid()=" << extDirAbsPath.isValid()<<extDirAbsPathStr;
//
QAndroidJniObject sharedFolder=QAndroidJniObject("java.io.File","(Ljava/lang/String;)V",
extDirAbsPath.object<jstring>());
qDebug() << __FUNCTION__ << "sharedFolder.isValid()=" << sharedFolder.isValid()<<sharedFolder.toString();
const jboolean sharedFolderCreated = sharedFolder.callMethod<jboolean>("mkdirs");
Q_UNUSED(sharedFolderCreated);
// ,
//
QAndroidJniObject suggestedFilePath = QAndroidJniObject::fromString(extDirAbsPathStr+"/"+"_tmp.jpg");
qDebug() << __FUNCTION__ << "suggestedFilePath.isValid()=" << suggestedFilePath.isValid()<<suggestedFilePath.toString();
//
//
QAndroidJniObject tempImgFile=QAndroidJniObject("java.io.File","(Ljava/lang/String;)V",
suggestedFilePath.object<jstring>());
qDebug() << __FUNCTION__ << "fileExistsCheck.isValid()=" << tempImgFile.isValid()<<tempImgFile.toString();
// ,
if (tempImgFile.isValid()){
const jboolean deleted = tempImgFile.callMethod<jboolean>("delete");
Q_UNUSED(deleted);
}
//
const jboolean fileCreated = tempImgFile.callMethod<jboolean>("createNewFile");
Q_UNUSED(fileCreated);
//
tempImgAbsPath = tempImgFile.callObjectMethod("getAbsolutePath","()Ljava/lang/String;");
qDebug() << __FUNCTION__ << "tempImgAbsPath.isValid()=" << tempImgAbsPath.isValid()<<tempImgAbsPath.toString();
// authority fileprovider
const QString contextFileProviderStr ("org.qtproject.example.qsketch.fileprovider");
const char androidFileProvider [] = "android/support/v4/content/FileProvider";
//const char androidxFileProvider [] = "androidx/core/content/FileProvider"; - Qt
/*QAndroidJniObject*/ tempImgURI = QAndroidJniObject::callStaticObjectMethod(androidFileProvider, "getUriForFile", "(Landroid/content/Context;Ljava/lang/String;Ljava/io/File;)Landroid/net/Uri;",
context.object<jobject>(), QAndroidJniObject::fromString(contextFileProviderStr).object<jstring>(), tempImgFile.object<jobject>());
qDebug() << __FUNCTION__ << "tempImgURI.isValid()=" << tempImgURI.isValid()<<tempImgURI.toString();
// MediaStore.EXTRA_OUTPUT
QAndroidJniObject MediaStore__EXTRA_OUTPUT
= QAndroidJniObject::getStaticObjectField("android/provider/MediaStore", "EXTRA_OUTPUT", "Ljava/lang/String;");
qDebug() << "MediaStore__EXTRA_OUTPUT.isValid()=" << MediaStore__EXTRA_OUTPUT.isValid();
// URI
intent.callObjectMethod("putExtra","(Ljava/lang/String;Landroid/os/Parcelable;)Landroid/content/Intent;",MediaStore__EXTRA_OUTPUT.object<jstring>(), tempImgURI.object<jobject>());
qDebug() << __FUNCTION__ << "intent.isValid()=" << intent.isValid();
QtAndroid::startActivity(intent, REQUEST_IMAGE_CAPTURE, this);
}
- Aux .
(.h) Aux :
#ifndef AUXFUNC_H
#define AUXFUNC_H
#include <QImage>
#include <QColor>
#include <QPainter>
#include <QMatrix>
#include <QSize>
#include <QPoint>
class Aux
{
public:
static void resizeCenteredImg(QImage *image, const QSize &newSize, const QColor bgColor);
static void rotateImg(QImage &img, qreal degrees);
static void rotateImgCW90(QImage &img);
static void rotateImgCW180(QImage &img);
static void rotateImgCW270(QImage &img);
};
#endif // AUXFUNC_H
(.cpp) Aux :
void Aux::resizeCenteredImg(QImage *image, const QSize &newSize, const QColor bgColor){
if (image->size() == newSize)
return;
const QSize szDiff = newSize - image->size();
QImage newImage(newSize, QImage::Format_ARGB32);
newImage.fill(bgColor);
QPainter painter(&newImage);
painter.drawImage(QPoint(szDiff.width()/2, szDiff.height()/2), *image);
*image = newImage;
}
void Aux::rotateImg(QImage &img, qreal degrees){
QPoint center = img.rect().center();
QMatrix matrix;
matrix.translate(center.x(), center.y());
matrix.rotate(degrees);
img = img.transformed(matrix, Qt::SmoothTransformation);
}
void Aux::rotateImgCW90(QImage &img){
const int w = img.width();
const int h = img.height();
const int maxDim = std::max(w, h);
resizeCenteredImg(&img, QSize(maxDim, maxDim), Qt::white);
rotateImg(img, 90);
resizeCenteredImg(&img, QSize(h, w), Qt::white);
}
void Aux::rotateImgCW180(QImage &img){
rotateImg(img, 180);
}
void Aux::rotateImgCW270(QImage &img){
const int w = img.width();
const int h = img.height();
const int maxDim = std::max(w, h);
resizeCenteredImg(&img, QSize(maxDim, maxDim), Qt::white);
rotateImg(img, 270);
resizeCenteredImg(&img, QSize(h, w), Qt::white);
}
.
«thumbnailNotFullScale». , , , . JNI-.
If the thumbnail is always oriented correctly, then the full-size image is directed in one direction and must be rotated. Information about the required transformations can be obtained from the exif properties of the image using the ExifInterface . In the Java examples found on the Internet , the conversion to the normal orientation is done in Java code, in the case of Qt there is no point in torturing yourself with difficult to debug, cumbersome JNI calls, and it is easier to perform all the necessary transformations in Qt.