Rendering error after changing the size of Window

[wangfys]

I'm trying to implement a simple image viewer. I hope the image viewer can show the image without scaling, so I read the documentation about Image and find that I can use sourceSize property to get the real size. But there is something wrong after I change the size of Window to fit the size of the image.
I use a FileDialog to choose a file and dynamiclly create a new Window to show the image.

FileDialog {
        id: fileDialog
        title: "Choose a file"
        folder: shortcuts.home
        onAccepted: {
            var image = Qt.createComponent("qrc:/image.qml").createObject(appWindow, {});
            image.data[1].source = this.fileUrl;
        }
}

And this is my image.qml

import QtQuick 2.11
import QtQuick.Window 2.11
import QtQuick.Controls 1.4
Window {
    id: imageWindow
    visible: true
    width: 200
    height: 200
    ToolBar {
        height: 50
        Row {
            ToolButton {
                width: 70
                height: 45
                text: qsTr("Exit")
                onClicked: imageWindow.close()
            }
        }
    }
    Image {
        id: showImage
        y: 50
        onSourceSizeChanged: {
            imageWindow.height = this.sourceSize.height + 50;
            imageWindow.width = this.sourceSize.width;
        }
    }
}

I tried to change the Window's size when receiving sourceChanged signal, but failed because at that time, sourceSize is still (0, 0). So I choose to change the Window's size when receiving sourceSizeChanged signal.

This image for test is 256*256:

And I get a result like this:

There is an empty hole that looks like 200*200. After I drag the edge of the window it becomes normal immediately.

So what's wrong with this process?

[Diracsbracket]

@wangfys
Really strange indeed. I tested your code, and it is perfectly working, for any images I use, including yours. I tested on Win10, Qt 5.11.0. Using onSourceChanged instead does indeed not work.

Aside from not being very useful here, why not writing something like

Window {
    id: imageWindow
    ...
    property alias showImage: showImage
    ...
    Image {
         id: showImage
         ...
    }

and then use

image.showImage.source = this.fileUrl;

instead of

image.data[1].source = this.fileUrl;

[wangfys]

@Diracsbracket Thanks for the suggestion!

I find this problem only occurs when opening the first image.

It's very confusing.

And I try to avoid the problem by setting the Window invisible at first and then setting it visible after source is set.
But I face another problem now. I add a feature for my program. I want to draw something. (In fact I'm doing a homework about image warping. I need to set some control points)

Here is the effect:

I draw some lines but nothing is showed.
Then I pressed Exit button and keep pressed while exiting the button area so the button won't get a clicked signal and the Window won't close.

Now everything works fine. Maybe there's something wrong that the program can't refresh or update rendering automatically at first.

I implemented the drawing function according to the document about Scene Graph - Custom Geometry

Here is my new version of image.qml

import QtQuick 2.11
import QtQuick.Window 2.11
import QtQuick.Controls 1.4

import CustomItem 1.0

Window {
    id: imageWindow
    visible: false
    width: 200
    height: 200
    property alias showImage: showImage
    ToolBar {
        height: 50
        Row {
            ToolButton {
                width: 70
                height: 45
                text: qsTr("Exit")
                onClicked: imageWindow.close()
            }
        }
    }
    Image {
        id: showImage
        y: 50
        onSourceSizeChanged: {
            imageWindow.height = this.sourceSize.height + 50;
            imageWindow.width = this.sourceSize.width;
            mouse.height = this.sourceSize.height;
            mouse.width = this.sourceSize.width;
            canvas.height = this.sourceSize.height;
            canvas.width = this.sourceSize.width;
        }
    }
    MouseArea {
        id: mouse
        y: 50
        hoverEnabled: true
        property bool draw: false
        onPressed: {
            draw = true;
            points.addPoint(Qt.point(this.mouseX, this.mouseY));
            points.addPoint(Qt.point(this.mouseX, this.mouseY));
        }
        onPositionChanged: {
            if (draw === true)
            {
                points.setCurrentPoint(Qt.point(this.mouseX, this.mouseY));
            }
        }
        onReleased: draw = false;
    }
    Rectangle {
        id: canvas
        y: 50
        color: "transparent"
        MyPointPairs {
            id: points
        }
    }
}

I use qmlRegisterType<pointpairs>("CustomItem", 1, 0, "MyPointPairs"); in main.cpp to register pointpairs and here is my pointpairs.h

#ifndef POINTPAIRS_H
#define POINTPAIRS_H

#include <QQuickItem>

class pointpairs: public QQuickItem
{
    Q_OBJECT
public:
    pointpairs(QQuickItem *parent=nullptr);
    ~pointpairs();

    QSGNode *updatePaintNode(QSGNode *oldNode, UpdatePaintNodeData *);

public slots:
    void addPoint(const QPointF &p);
    void setCurrentPoint(const QPointF &p);

private:
    QVariantList points;
};

#endif // CLIENT_H

and pointpairs.cpp

#include "pointpairs.h"

#include <QSGNode>
#include <QSGFlatColorMaterial>

pointpairs::pointpairs(QQuickItem *parent)
    : QQuickItem(parent)
{
    setFlag(ItemHasContents, true);
}

pointpairs::~pointpairs()
{
}

QSGNode *pointpairs::updatePaintNode(QSGNode *oldNode, UpdatePaintNodeData *)
{
    QSGGeometryNode *node = nullptr;
    QSGGeometry *geometry = nullptr;

    if (!oldNode)
    {
        node = new QSGGeometryNode;
        geometry = new QSGGeometry(QSGGeometry::defaultAttributes_Point2D(), points.count());
        geometry->setLineWidth(20);
        geometry->setDrawingMode(QSGGeometry::DrawLines);
        node->setGeometry(geometry);
        node->setFlag(QSGNode::OwnsGeometry);
        QSGFlatColorMaterial *material = new QSGFlatColorMaterial;
        material->setColor(QColor(255, 165, 0));
        node->setMaterial(material);
        node->setFlag(QSGNode::OwnsMaterial);
    }
    else
    {
        node = static_cast<QSGGeometryNode *>(oldNode);
        geometry = node->geometry();
        geometry->allocate(points.count());
    }
    QSGGeometry::Point2D *vertices = geometry->vertexDataAsPoint2D();
    for (int i=0; i<points.count(); ++i)
    {
        vertices[i].set(points[i].toPointF().x(), points[i].toPointF().y());
    }
    node->markDirty(QSGNode::DirtyGeometry);
    return node;
}

void pointpairs::addPoint(const QPointF &p)
{
    points << p;
    update();
}

void pointpairs::setCurrentPoint(const QPointF &p)
{
    points[points.count() - 1] = p;
    update();
}

[Diracsbracket]

@wangfys
I got exactly the same behavior as you. Although I never used the scene graph before, your example (+ the doc and the Custom Geometry example in Qt's examples) gave me a little crash course in the topic.
http://doc.qt.io/qt-5/qtquick-visualcanvas-scenegraph.html

Your example really should work as it seems you did everything as required by the doc. At my side, the lines become visible once I hover the mouse one the exit button. Possibly this is a bug?

PS. Again, not being useful, I maybe I could suggest you to change the definition of your points from QVariantList points; to QVector<QPointF> points;

Then you can use:

        const float x = static_cast<float>(points[i].x());
        const float y = static_cast<float>(points[i].y());
        vertices[i].set(x, y);

rather than

      vertices[i].set(points[i].toPointF().x(), points[i].toPointF().y());

as it saves you a couple of calls to toPointF().