Canvas/QPainter bug

f.serreau

Hi everyone,

I use Qt 5.11 and QtQuick 2.11, on windows OS.
I do have a bug on one of my application:
"
QPainter::begin: Paint device returned engine == 0, type: 3
QPainter::setRenderHint: Painter must be active to set rendering hints
QPainter::setRenderHint: Painter must be active to set rendering hints
QPainter::setCompositionMode: Painter not active
QPainter::scale: Painter not active
QPainter::worldTransform: Painter not active
QPainter::worldTransform: Painter not active
QPainter::setWorldTransform: Painter not active
QPainter::pen: Painter not active
QPainter::setPen: Painter not active
QPainter::brush: Painter not active
QPainter::setBrush: Painter not active
QPainter::font: Painter not active
QPainter::setFont: Painter not active
QPainter::opacity: Painter not active
QPainter::compositionMode: Painter not active
QPainter::setClipping: Painter not active, state will be reset by begin
QPainter::pen: Painter not active
QPainter::setPen: Painter not active
QPainter::pen: Painter not active
QPainter::setPen: Painter not active
QPainter::pen: Painter not active
QPainter::setPen: Painter not active
QPainter::compositionMode: Painter not active
QPainter::setCompositionMode: Painter not active
QPainter::setCompositionMode: Painter not active
QPainter::pen: Painter not active
QPainter::setPen: Painter not active
QPainter::pen: Painter not active
QPainter::setPen: Painter not active
QPainter::pen: Painter not active
QPainter::setPen: Painter not active
QPainter::end: Painter not active, aborted
"

And the area that is supposed to be painted is filled with black instead.

In order to isolate the problem I made a small application that can reproduce the bug:

"
import QtQuick 2.11
import QtQuick.Window 2.2
import QtQuick.Controls 2.4 as QtQuick2
import QtQuick.Controls 1.4 as QtQuick1

Window {
visible: true
width: 1024
height: 768
title: qsTr("Hello World")
id:mainWindow

QtQuick2.ScrollView {
    id: myScrollView
    anchors.fill: parent
    property real scaleFactor: 1
    onScaleFactorChanged: myCanvas.requestPaint()

    contentItem: Canvas {
        id: myCanvas
        width: 200 * myScrollView.scaleFactor;
        height: 200 * myScrollView.scaleFactor

        onPaint: {
            var ctx = getContext("2d")
            ctx.save()
            ctx.lineWidth = 4
            ctx.strokeStyle = "blue"
            ctx.fillStyle = "steelblue"
            ctx.beginPath()
            ctx.moveTo(0,0)
            ctx.lineTo(myCanvas.width,0)
            ctx.lineTo(myCanvas.width,myCanvas.height)
            ctx.lineTo(0,myCanvas.height)
            ctx.closePath()
            ctx.fill()
            ctx.stroke()
            ctx.restore()
        }
    }
}

MouseArea {
    anchors.fill: parent
    onWheel: {
        if (true )
        {
            myScrollView.scaleFactor += 0.2 * wheel.angleDelta.y / 120;
            if (myScrollView.scaleFactor < 0)
            {
                myScrollView.scaleFactor = 0;
            }
            console.log(myScrollView.scaleFactor)
        }
    }
}

}
"

In this application when you scroll (zoom in) for a while, the error occurs and the view is filled with "blue" (#0000FF).

I am using Canvas in my application. I also tried using QQuickPaintedtem or QQuickItem.
With QQuickPaintedtem I still have the bug.
With QQuickItem I do not have the bug no more but the render is very slow.
Besides, I find Canvas convenient in order to draw, I would appreciate to keep using them.

Does the problem come from the update/requestPaint method call on a wheel event?
Is there any other solution in order to implement my zoom function?

Regards,

Diracsbracket

Hi @f.serreau
I have tested your example, and it works correctly with no errors.
I tested it on Windows 10 (Fall Update), MS VS2017 and Qt 5.11.0.

penpen 0

Hello, I encountered the same problem as you, did you solve it, it will be black or blue screen when zoomed in