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I am trying to use skia with qml. I am inheriting from QQuickPaintedItem. I have modified this exanple, http://doc.qt.io/qt-5/qtquick-customitems-painteditem-example.html to use QQuickPaintedItem::FramebufferObject as renderTarget. I am trying to create SkSurface from existing texture from QQuickPaintedItem. I am always getting null. Please let me know If it is possible to use existing texture from qml item and use it for skia rendering.

main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include "textballoon.h"

int main(int argc, char *argv)

 QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);

 QGuiApplication app(argc, argv);


 QQmlApplicationEngine engine;
 qmlRegisterType<TextBalloon>("com.sanjay.check", 1, 0, "TextBalloon");
 engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
 if (engine.rootObjects().isEmpty())
 return -1;

 return app.exec();

project.pro file

QT += quick
CONFIG += c++11

# The following define makes your compiler emit warnings if you use
# any feature of Qt which as been marked deprecated (the exact warnings
# depend on your compiler). Please consult the documentation of the
# deprecated API in order to know how to port your code away from it.
DEFINES += QT_DEPRECATED_WARNINGS

# You can also make your code fail to compile if you use deprecated APIs.
# In order to do so, uncomment the following line.
# You can also select to disable deprecated APIs only up to a certain version of Qt.
#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000 # disables all the APIs deprecated before Qt 6.0.0

SOURCES += 
 main.cpp 
 textballoon.cpp

RESOURCES += qml.qrc

# Additional import path used to resolve QML modules in Qt Creator's code model
QML_IMPORT_PATH =

# Additional import path used to resolve QML modules just for Qt Quick Designer
QML_DESIGNER_IMPORT_PATH =

# Default rules for deployment.
qnx: target.path = /tmp/$$TARGET/bin
else: unix:!android: target.path = /opt/$$TARGET/bin
!isEmpty(target.path): INSTALLS += target

HEADERS += 
 textballoon.h

INCLUDEPATH +=
/home/sanju/skia/include/core 
/home/sanju/skia/src/core 
/home/sanju/skia/include/private 
/home/sanju/skia/include/config 
#/home/sanju/skia/tools/ 
/home/sanju/skia/include/gpu 
/home/sanju/skia/src/gpu 
/home/sanju/skia/src/gpu/gl 
#/home/sanju/skia/include/effects 
/home/sanju/skia/include/encode 
/home/sanju/skia/include/utils 

unix:!macx: LIBS += -L$$PWD/../../skia/out/Release/ -lskia

INCLUDEPATH += $$PWD/../../skia/out/Release
DEPENDPATH += $$PWD/../../skia/out/Release

Here is my modified textballoon.cpp file

#include "GrContext.h"
#include "gl/GrGLTypes.h"
//#include "GrGLTexture.h"

#include "textballoon.h"

#include "gl/GrGLInterface.h"
#include "SkData.h"
#include "SkImage.h"
#include "SkStream.h"
#include "SkSurface.h"
//#include "GrGpu.h"
#include "GrBackendSurface.h"
//#include "GrContextPriv.h"
//#include "GrGpu.h"

#include <QtDebug>
//! [0]
TextBalloon::TextBalloon(QQuickItem *parent)
 : QQuickPaintedItem(parent)
 , rightAligned(false)

 setRenderTarget(QQuickPaintedItem::FramebufferObject);
 setRightAligned(true);

 QObject::connect(this, &QQuickPaintedItem::widthChanged, this, [this]() 
 // qDebug() << "textureChanged";
 this->dirty = true;
 );

//! [0]

//! [1]
void TextBalloon::paint(QPainter *painter)

 QBrush brush(QColor("#007430"));

 painter->setBrush(brush);
 painter->setPen(Qt::NoPen);
 painter->setRenderHint(QPainter::Antialiasing);

 QSizeF itemSize = size();
 painter->drawRoundedRect(0, 0, itemSize.width(), itemSize.height() - 10, 10, 10);

 if (rightAligned)
 
 const QPointF points[3] = 
 QPointF(itemSize.width() - 10.0, itemSize.height() - 10.0),
 QPointF(itemSize.width() - 20.0, itemSize.height()),
 QPointF(itemSize.width() - 30.0, itemSize.height() - 10.0),
 ;
 painter->drawConvexPolygon(points, 3);
 
 else
 
 const QPointF points[3] = 
 QPointF(10.0, itemSize.height() - 10.0),
 QPointF(20.0, itemSize.height()),
 QPointF(30.0, itemSize.height() - 10.0),
 ;
 painter->drawConvexPolygon(points, 3);
 

 if(textureProvider())
 
 sk_sp<const GrGLInterface> interface = nullptr;
 // Leaving interface as null makes Skia extract pointers to OpenGL functions for the current
 // context in a platform-specific way. Alternatively, you may create your own GrGLInterface and
 // initialize it however you like to attach to an alternate OpenGL implementation or intercept
 // Skia's OpenGL calls.
 sk_sp<GrContext> context = GrContext::MakeGL(interface);
 if (!context) 
 SkDebugf("GrContext::MakeGL returned nulln");
 

 // GrGpu* gpu = context->contextPriv().getGpu();

 QSGTexture* texture = textureProvider()->texture();
 if(texture)
 
 qDebug() << "Texture exist";
 QSurfaceFormat format = QSurfaceFormat::defaultFormat();
 QSize size = texture->textureSize();
 qDebug() << size;


 qDebug() << "Texture id " << texture->textureId() << " alpha channel " << texture->hasAlphaChannel()
 << "FORMAT RGB" << format.depthBufferSize() << " sample size " << format.samples();


 GrGLTextureInfo info;
 info.fID = texture->textureId();
 info.fFormat = SkColorType::kUnknown_SkColorType;
 GrBackendTexture grTexture(size.width(),
 size.height(),
 texture->hasMipmaps()? GrMipMapped::kYes : GrMipMapped::kNo,
 info);

 GrGLFramebufferInfo fboInfo;
 fboInfo.fFBOID = texture->textureId();

 auto surface = SkSurface::MakeFromBackendTexture(context.get(),
 grTexture,
 GrSurfaceOrigin::kTopLeft_GrSurfaceOrigin,
 0,
 SkColorType::kUnknown_SkColorType,
 nullptr,
 nullptr);

// GrGLFramebufferInfo fboInfo;
// fboInfo.fFBOID = texture->textureId();

// GrBackendRenderTarget backendTarget(size.width(),
// size.height(),
// 0,
// 0,
// fboInfo);
// auto surface = SkSurface::MakeFromBackendRenderTarget(context.get(),
// backendTarget,
// GrSurfaceOrigin::kTopLeft_GrSurfaceOrigin,
// SkColorType::kUnknown_SkColorType,
// nullptr,
// nullptr);
 if(surface)
 
 qDebug() << "Surface created";
 
 
 

//! [1]

bool TextBalloon::isRightAligned()

 return this->rightAligned;


void TextBalloon::setRightAligned(bool rightAligned)

 this->rightAligned = rightAligned;