control the angle

[chris_rookie]

I saw an example of qml. UI Components: Dial Control Example.
I don't understand how to caculate the angel.

[IntruderExcluder]

The angle property is read-only, instead of this you should use value property.

[chris_rookie]

@IntruderExcluder
Yes. I know what you mean.
Here is the code.I just don't know "angle: Math.min(Math.max(-130, root.value*2.6 - 130), 133)" mean.

Image {
    id: needle
    x: 98; y: 33
    antialiasing: true
    source: "needle.png"
    transform: Rotation {
        id: needleRotation
        origin.x: 5; origin.y: 65
        //! [needle angle]
        **angle: Math.min(Math.max(-130, root.value*2.6 - 130), 133)**
        Behavior on angle {
            SpringAnimation {
                spring: 1.4
                damping: .15
            }
        }
        //! [needle angle]
    }
}

[Pablo J. Rogina]

@chris_rookie said in control the angle:

I just don't know "angle: Math.min(Math.max(-130, root.value*2.6 - 130), 133)" mean.

It's a formula to calculate the angle for drawing the needle :-)

And the angle is then used to animate a Behavior:

A Behavior defines the default animation to be applied whenever a particular property value changes.

In your case the property that changes is angle which in turn is dependent on root.value

[chris_rookie]

@Pablo-J-Rogina
Thanks for your answer.
After reading this page ```
https://doc.qt.io/qt-5/qml-qtquick-rotation.html

I think I understand what "angle: Math.min(Math.max(-130, root.value*2.6 - 130), 133)" mean

[chris_rookie]

@IntruderExcluder
Thanks for your answer.