import QtQuick 2.8
import QtQuick.Window 2.2
import QtQuick.Controls 2.1

Window {
    id: root
    visible: true
    width: Screen.width
    height: Screen.height
    title: qsTr("Canvas Bug : click on the drawing, if it works it says ok")
    
    
    Canvas{
        id: theCanvas
        anchors.fill: parent
        
        renderStrategy: Canvas.Threaded
        
        onPaint: {
            var ctx = getContext("2d");
            
            ctx.reset();
            ctx.clearRect(0, 0, width, height);
                
            ctx.save();
                    
            ctx.strokeStyle="yellow";
            ctx.lineWidth=Screen.pixelDensity*2;
    
            ctx.moveTo(0,height);
            ctx.lineTo(width,0);
                    
            ctx.stroke();
                    
            ctx.restore();
        }
        
        MouseArea{
            anchors.fill: parent

            readonly property int mouseRegionSize : 8 // the tolerance for click detect

            function found(mouse)
            {
                var ctx = theCanvas.getContext("2d");
                var imgPixel;
                
                // workaround  for 5.8 :
                /*if(Qt.platform.os=="windows")
                    imgPixel = ctx.getImageData((mouse.x-(mouseRegionSize/(2*Screen.pixelDensity))),(mouse.y-(mouseRegionSize/(2*Screen.pixelDensity))),mouseRegionSize/Screen.pixelDensity,mouseRegionSize/Screen.pixelDensity);
                else
                    imgPixel = ctx.getImageData((mouse.x*Screen.pixelDensity/2-(mouseRegionSize/2)),(mouse.y*Screen.pixelDensity/2-(mouseRegionSize/2)),mouseRegionSize,mouseRegionSize);*/
                
                // code that worked in 5.7 :
                    imgPixel = ctx.getImageData(mouse.x-mouseRegionSize/2,mouse.y-mouseRegionSize/2,mouseRegionSize,mouseRegionSize);
                
                
                for(var i=0; i<imgPixel.width*imgPixel.height; i++)
                    if(imgPixel.data[3+(4*i)]) // alpha channel
                        return true;

                return false;
            }

            onPressed: {
                if(found(mouse))
                    popup.createObject(theCanvas).open();
            }
        }
        
        Component{
            id: popup
            
            Dialog{
                x: (parent.width-width)/2
                y: (parent.height-height)/2
                Label{
                    text: "ok"
                }
            }
        }
    }
}