QChart Range / TickCount Question

[Rich Bair]

I have a report from the field on 5.12.x on a chart.

I have the following code with a file with maxTime = 106.4 and printerTimeScale = 0 (1min blocks).

            // *** Chart Area ***
            int numBlocks = 0;
            switch(printerTimeScale) {
            default:
            case 0:
                numBlocks = static_cast<int>(maxTime) + 1;
                break;
            case 1:
                numBlocks = static_cast<int>(maxTime/2.0 + (static_cast<int>(maxTime) % 2) + 1);
                break;
            case 2:
                numBlocks = static_cast<int>(maxTime/5.0 + (static_cast<int>(maxTime) % 5) + 1);
                break;
            }

            reinterpret_cast<QValueAxis*>(chart.axes()[0])->setTickCount(numBlocks + 1);
            reinterpret_cast<QValueAxis*>(chart.axes()[0])->setRange(0.0, numBlocks*((printerTimeScale == 0) ? 1.0 : (printerTimeScale == 1) ? 2.0 : 5.0));

The data ends at 106.4 minutes as expected and the last column #107 runs from 107.0 to 108.0.

All good so far. However, if I go to day column #40 it runs from 39.4 to 40.4...why?

Where is this decimal coming from?

Thanks,
-Rich

[SGaist]

Hi,

Can you compare that behaviour to a more recent version of Qt ? At least 5.15.

[Rich Bair]

On windows I cannot replicate using 6.10.2. I'm trying to get 5.12 installed on this same system to see if that's related.

[Joe von Habsburg]

@Rich-Bair said in QChart Range / TickCount Question:

107.0 to 108.0.

Maybe, it's about

void QValueAxis::setRange(qreal min, qreal max)
setTickInterval(qreal insterval)

or you can check with these

void QValueAxis::minChanged(qreal min)
void QValueAxis::maxChanged(qreal max)
tickIntervalChanged(qreal interval)

Because your code its calculate true.

int getNum(int printerTimeScale, double maxTime){
    int numBlocks = 0;
    switch(printerTimeScale) {
    default:
    case 0:
        numBlocks = static_cast<int>(maxTime) + 1;
        break;
    case 1:
        numBlocks = static_cast<int>(maxTime/2.0 + (static_cast<int>(maxTime) % 2) + 1);
        break;
    case 2:
        numBlocks = static_cast<int>(maxTime/5.0 + (static_cast<int>(maxTime) % 5) + 1);
        break;
    }
    return numBlocks;
}

    double maxTime = 106.4;
    qDebug() << "getNum 0" << getNum(0, maxTime); //getNum 0 107
    qDebug() << "getNum 1" << getNum(1, maxTime); //getNum 1 54
    qDebug() << "getNum 2" << getNum(2, maxTime); //getNum 2 23

    maxTime = 39.4;
    qDebug() << "getNum 0" << getNum(0, maxTime); //getNum 0 40
    qDebug() << "getNum 1" << getNum(1, maxTime); //getNum 1 21
    qDebug() << "getNum 2" << getNum(2, maxTime); //getNum 2 12

[Rich Bair]

I tested on windows 5.12.12 and 6.10.2...no joy. The only way I can make the symptom appear is if I do something like change the range with the multiplier:

            int numBlocks = 0;
            switch(printerTimeScale) {
            default:
            case 0:
                numBlocks = static_cast<int>(maxTime) + 1;
                break;
            case 1:
                numBlocks = static_cast<int>(maxTime/2.0 + (static_cast<int>(maxTime) % 2) + 1);
                break;
            case 2:
                numBlocks = static_cast<int>(maxTime/5.0 + (static_cast<int>(maxTime) % 5) + 1);
                break;
            }

            reinterpret_cast<QValueAxis*>(chart.axes()[0])->setTickCount(numBlocks + 1);
            reinterpret_cast<QValueAxis*>(chart.axes()[0])->setRange(0.0, numBlocks*((printerTimeScale == 0) ? **1.01** : (printerTimeScale == 1) ? 2.0 : 5.0));

[Joe von Habsburg]

How much does it affect you if the graph's boundaries grow by one unit? If the graph is drawn correctly, there shouldn't be a problem.