[Solved] Drawing Linear graph using QML canvas

[vishnu]

@p3c0
I got a new error
Cannot read property 'length' of undefined
I have defined the properties like this

 property var physicalValue_x: []
    property var physicalValue_z: []
    property var logicalValue_x: [-80,-40,40,80,220,400,740,680,170,-170,-250,-220,-80,-40,-20]
    property var logicalValue_z: [820,820,820,820,780,670,560,305,295,285,380,780,820,820,820]

function map(value,srcMax,srcMin,dstMax,dstMin){
        //        console.log(srcMax,srcMin,dstMax,dstMin," value ",value)
        return Number(((((dstMax - dstMin)*(value - srcMin)/(srcMax - srcMin))+dstMin)).toFixed(1)) ;
    }

    function logicalToPhysical()
    {
//        if(root.physicalValue_x)
        for(var i=0;i<logicalValue_z.length;i++)//error 'length undefined'
        {
            var pos_x = root.map(logicalValue_x[i],maxRange_x,minRange_x,x1,x0)
            physicalValue_x[i] = pos_x
            var pos_z = root.map(logicalValue_z[i],maxRange_z,minRange_z,y1,y0)
            physicalValue_z[i] = pos_z // here type error
        }
        console.log("physical x values"+physicalValue_x)
        console.log("physical z values"+physicalValue_z)
    }

if i uncomment the checkif(root.physicalValue_x) i get the error at for loop Cannot read property 'length' of undefined.
If I comment it i get 'TypeError: Type error' at physicalValue_z[i] = pos_z also 'TypeError: Cannot read property '0' of undefined' at var pos_z. I think the properties are not instantiated properly but eventually they will. What is the best practice to avoid these errors. Thanks

[p3c0]

@vishnu This means it is out of its scope. Access logicalValue_z just like you accessed physicalValue_x using root.

[vishnu]

@p3c0
As you said i have changed like this

 function logicalToPhysical()
    {
//        if(root.physicalValue_x)
        for(var i=0;i<root.logicalValue_x.length;i++)
        {
            var pos_x = root.map(root.logicalValue_x[i],root.maxRange_x,root.minRange_x,root.x1,root.x0)
            root.physicalValue_x[i] = pos_x
            var pos_z = root.map(root.logicalValue_z[i],root.maxRange_z,root.minRange_z,root.y1,root.y0) // here is the error
            root.physicalValue_z[i] = pos_z
        }
        console.log("physical x values"+root.physicalValue_x)
        console.log("physical z values"+root.physicalValue_z)
    }

But still the error TypeError: Cannot read property '0' of undefined at var pos_z;
FIY:these are the properties in addition to above properties

  property real y0 : 50.0;
    property real y1 : chart.height - chart.xAxisHeight
    property real x0 : chart.yAxisWidth
    property real x1 : chart.width - 100

[p3c0]

@vishnu Did Cannot read property 'length' of undefined for logicalValue_z go ?
For the other check which of the other properties is not accessible.

[vishnu]

@p3c0
Nope. if put the check if(root.physicalValue_x). The error TypeError: Cannot read property 'length' of undefined still appears at for(var i=0;i<root.logicalValue_x.length;i++).If I dont put the check then i get TypeError: Cannot read property '0' of undefined at var pos_z = root.map(root.logicalValue_z[i],root.maxRange_z,root.minRange_z,root.y1,root.y0).

[p3c0]

@vishnu Can you post a minimal example which replicates above scenario ? Something is not clear here.

[vishnu]

@p3c0
okay.

Rectangle {
    id: root
    width: 1280; height: 800
    property var physicalValue_x: []
    property var physicalValue_z: []
    property var logicalValue_x: [-80,-40,40,80,220,400,740,680,170,-170,-250,-220,-80,-40,-20]
    property var logicalValue_z: [820,820,820,820,780,670,560,305,295,285,380,780,820,820,820]

    property int maxRange_x: 1040
    property int minRange_x: -400
    property int maxRange_z: 1020
    property int minRange_z: 100
    property real y0 : 50.0;
    property real y1 : chart.height - chart.xAxisHeight
    property real x0 : chart.yAxisWidth
    property real x1 : chart.width - 100

    function map(value,srcMax,srcMin,dstMax,dstMin){
        return Number(((((dstMax - dstMin)*(value - srcMin)/(srcMax - srcMin))+dstMin)).toFixed(1)) ;
    }

    function logicalToPhysical()
    {
        for(var i=0;i<root.logicalValue_x.length;i++)
        {
            var pos_x = root.map(root.logicalValue_x[i],root.maxRange_x,root.minRange_x,root.x1,root.x0)
            root.physicalValue_x[i] = pos_x
            var pos_z = root.map(root.logicalValue_z[i],root.maxRange_z,root.minRange_z,root.y1,root.y0)
            root.physicalValue_z[i] = pos_z
        }
        console.log("physical x values"+root.physicalValue_x)
        console.log("physical z values"+root.physicalValue_z)
    }
Item{
        id:root_chart
        //        anchors.fill: parent
        anchors.left: root_checkbox.right
        height: parent.height
        anchors.right: parent.right
        Canvas {
            id: chart
            property int maxPoints: 200
            Component.onCompleted: {
                logicalToPhysical();/
            }
        onWidthChanged: {
                console.log("chart width is changing ")
                logicalToPhysical() //call 1 
                requestPaint()
            }
            onHeightChanged: {
                console.log("chart height is changing ")
                logicalToPhysical()// call 2
                requestPaint()
            }
     }

I found that because of these calls 1 and 2 the error is coming.

[p3c0]

@vishnu This doesnot show any error specific to what you posted earlier.

[vishnu]

@p3c0
I think i better post the whole file. sorry for the inconvenience.

import QtQuick 2.4
import QtQuick.Controls 1.2
Rectangle {
    id: root
    width: 1280; height: 800

    property variant data1: [20.0]
    property double currentPos_x:591
    property double currentPos_y:60
    property double currentPos_z:193

    property var physicalValue_x: []
    property var physicalValue_z: []
    property var logicalValue_x: [-80,-40,40,80,220,400,740,680,170,-170,-250,-220,-80,-40,-20]
    property var logicalValue_z: [820,820,820,820,780,670,560,305,295,285,380,780,820,820,820]

    property double showPos_x
    property double showPos_y
    property double showPos_z


    property int maxRange_x: 1040
    property int minRange_x: -400
    property int maxRange_z: 1020
    property int minRange_z: 100
    property real y0 : 50.0;
    property real y1 : chart.height - chart.xAxisHeight
    property real x0 : chart.yAxisWidth
    property real x1 : chart.width - 100

    function map(value,srcMax,srcMin,dstMax,dstMin){
        //        console.log(srcMax,srcMin,dstMax,dstMin," value ",value)
        return Number(((((dstMax - dstMin)*(value - srcMin)/(srcMax - srcMin))+dstMin)).toFixed(1)) ;
    }

    function logicalToPhysical()
    {
        for(var i=0;i<root.logicalValue_x.length;i++)
        {
            var pos_x = root.map(root.logicalValue_x[i],root.maxRange_x,root.minRange_x,root.x1,root.x0)
            root.physicalValue_x[i] = pos_x
            var pos_z = root.map(root.logicalValue_z[i],root.maxRange_z,root.minRange_z,root.y1,root.y0)
            root.physicalValue_z[i] = pos_z
        }
        console.log("physical x values"+root.physicalValue_x)
        console.log("physical z values"+root.physicalValue_z)
    }

    function inputToGraph(byteIndex,bitIndex,bitValue){

        if(bitIndex === -1){
            if(byteIndex === 36){
                //update x position
                showPos_x=Number((bitValue/1000).toFixed(1));
                var pos_x= root.map(bitValue/1000,maxRange_x,minRange_x,x1,x0);
                currentPos_x=pos_x;
//                console.log("current pos x map value"+currentPos_x)
            }
            if(byteIndex === 40){
                //update y position
                showPos_y=Number((bitValue/1000).toFixed(1));
                currentPos_y=bitValue/1000;
                //                console.log("current pos y map value"+currentPos_y)
            }
            if(byteIndex === 44){
                //update z position
                showPos_z=Number((bitValue/1000).toFixed(1));
                var pos_z= root.map(bitValue/1000,maxRange_z,minRange_z,y1,y0);
                currentPos_z=pos_z;
//                console.log("current pos z map value"+currentPos_z)
            }
        }
    }

    Connections{
        target: tcpCommunicationPort
        onDataFromCpp:{
            inputToGraph(byteIndex,bitIndex,bitValue)
        }
    }
    Rectangle{
        id:root_checkbox
        anchors.left: parent.left
        width: parent.width/4
        height: parent.height
        Row{
            spacing: 50
            anchors.centerIn: parent
            Rectangle{
                width: triggerButton.width
                height: triggerButton.height
                border.color: "red"
                TextInput{
                    id: timeInput
                    anchors.centerIn: parent
                }
            }
            Button{
                id:triggerButton
                text:"trigger"
                onClicked: {
                    //                    var y0 = 50.0;
                    //                    var y1 = chart.height - chart.xAxisHeight
                    //                    var x0 = chart.yAxisWidth
                    //                    var x1 = chart.width - 100
                    //                    var mappedzvalue = root.map(521,maxRange_x,minRange_x,x1,x0);
                    //                    //                                        point2.ypos = mappedzvalue
                    //                    var mappedxvalue = root.map(717,maxRange_z,minRange_z,y1,y0)
                    //                    //                                        point2.xpos =Number((mappedxvalue).toFixed(1))
                    //                    console.log("mapped z value",mappedzvalue)
                    //                    console.log("mapped x value",mappedxvalue)
                    inputToGraph(36,-1,0);
                    inputToGraph(44,-1,0);
                }
            }
            Button{
                id:triggerButton1
                text:"trigger1"
                onClicked: {
                    console.log(" current ")
                }
            }
        }
    }


    Item{
        id:root_chart
        //        anchors.fill: parent
        anchors.left: root_checkbox.right
        height: parent.height
        anchors.right: parent.right
        Canvas {
            id: chart
            property int maxPoints: 200
            Component.onCompleted: {
                logicalToPhysical();
            }
            onWidthChanged: {
                console.log("chart width is changing ")
                if(root.physicalValue_x){
                    logicalToPhysical()
                    requestPaint()
                }
            }
            onHeightChanged: {
                console.log("chart height is changing ")
                logicalToPhysical()
                requestPaint()
            }

            width: parent.width
            height: parent.height
            anchors.margins: 50
            antialiasing: true
            renderStrategy: Canvas.Cooperative

            property color linecolor: "#808080"
            property color background: "#f5f5f5"

            //            property int yRef: chart.height/2 - chart.xAxisHeight
            //            property int xRef: chart.yAxisWidth + 100

            property int yAxisWidth: 80   // x pos of y-axis in pixel
            property int xAxisHeight: 40  // y distance of x-axis from bottom in pixel

            property bool fillAreas: false
            property int scalingFactor: 30

            function drawAxis(ctx) {
                var yAxis = {
                    labels: ["+6 dB", "0 dB", "-6 dB", "-12 dB", "-18 dB"],
                    lines: [0.0, 0.22, 0.44, 0.66, 0.88]
                }

                var xAxis = {
                    labels: ["100 mm", "150 mm", "200 mm", "250 mm", "300 mm",
                        "350 mm", "400 mm", "450 mm", "500 mm", "550 mm"],
                    lines: [0.0, 0.15, 0.25, 0.35, 0.50,
                        0.60, 0.70, 0.82, 0.92, 1.00]
                }

                //                var y0 = 50.0;
                //                var y1 = chart.height - chart.xAxisHeight
                //                var x0 = chart.yAxisWidth
                //                var x1 = chart.width - 100

                // clear
                ctx.fillStyle = background
                ctx.fillRect(0,0,width,height)

                // frame
                ctx.strokeStyle = linecolor;
                ctx.fillStyle = "#999999";
                ctx.lineWidth = 1

                ctx.beginPath();
                ctx.moveTo(x0,y0);

                ctx.lineTo(x1,y0);
                ctx.lineTo(x1,y1);
                ctx.lineTo(x0,y1);
                ctx.lineTo(x0,y0);
                ctx.stroke()

                var w
                var yp

                //drawing the small lines on the X and Y axis
                for (var y = 0; y < yAxis.lines.length; y++)
                {
                    ctx.beginPath();
                    ctx.strokeStyle = "black"
                    yp = (y1 - y0) * yAxis.lines[y] + y0
                    ctx.moveTo(x0 - 10, yp);
                    ctx.lineTo(x0, yp);
                    ctx.stroke();
                    ctx.closePath();

                    //                w = ctx.measureText(yAxis.labels[y]).width
                    //                ctx.fillText(yAxis.labels[y], x0 - w -5, yp + 5)
                }

                for (var x = 0; x < xAxis.lines.length; x++)
                {
                    ctx.beginPath();
                    var xp = (x1 - x0) * xAxis.lines[x] + x0
                    ctx.moveTo(xp, y1);
                    ctx.lineTo(xp, y1 + 5);
                    ctx.stroke();
                    ctx.closePath();

                    ctx.fillText(xAxis.labels[x], xp - 20, y1 + 20)
                }
                ctx.beginPath();
                console.log("drawing the graph")
                console.log("chart width"+ chart.width);

                ctx.moveTo(physicalValue_x[0],physicalValue_z[0]);
                for( var i=1;i< physicalValue_x.length;i++){
                    ctx.lineTo(physicalValue_x[i],physicalValue_z[i])
                }
                ctx.lineWidth = 2
                ctx.stroke();
                ctx.closePath();
            }
            onPaint: {
                var ctx = getContext("2d");
                //                ctx.save();
                drawAxis(ctx)
                //                ctx.restore();
            }
        }
        Rectangle {
            id: point1
            x: currentPos_x
            y: currentPos_z
            z:10
            radius: 5
            width: 60; height: 15
            color: "#800096d6"
            Text{
                id:currentpoisionText
                anchors.centerIn: parent
                text: showPos_x+","+showPos_z
            }
        }
    }
}

try to ignore the function inputToGraph and connections because it is from cpp side.

[p3c0]

@vishnu It appears to be the problem with the initialization of properties as well as the intialization of items from where these properties are accessed. It seems that when Canvas is created and its heightChanged signal is invoked the property logicalValue_z is not initialized yet and thus causes that error but very first time only. Later it doesnt seems to give that error. This can be avoided by adding another condition where you can check if that property is initialized just like you checked physicalValue_x

if(physicalValue_x && logicalValue_z){
    logicalToPhysical()
    requestPaint()
}

[vishnu]

@p3c0
perfect. May i know what does this mean exactly? if(physicalValue_x && logicalValue_z) . I am assuming at this point physicalValue_x!=0 and logicalValue_z !=0 .then it enters inside the condition.

[p3c0]

@vishnu The control will go ahead if and only if both properties are initialized. Its a normal & operation.