What are good pratices about games frame rates development

johngod

I am developing a qml game where I used a Timer with 60 fps for the game loop.
Posts like this https://forum.qt.io/topic/60063/smooth-character-movement and Qt Blog https://www.qt.io/blog/new-in-qt-6.4-frameanimation-element, explain that Timers have flaws and can cause choppy animations with different monitors refresh rates.
I naively replaced Timer with FrameAnimation, and character movement become smooth even with different monitors refresh rates.
All good until last week, when I bought a new gaming laptop with 144Hz, and my character movement become blazing fast, which is not ok, since it should be consistent in different laptops with different frame rates.
I read the FrameAnimation blog again with more attention and found I need to multiply the movement speed with frameTime. This seems to work, the following example is a moving cube, it seems to be at the same velocity in both my old and new laptops.

import QtQuick

Window {
    id: root
    width: 640
    height: 480
    visible: true
    title: qsTr("Hello World")

    property real mm: Screen.pixelDensity

    Rectangle {
        id: rect2
        property real direction: 1
        //use the frameTime to make the velocity independent from different refresh rates
        property real speedWalk: 20 * mm * direction * frameAnimation.frameTime

        //velocity varies according different refresh rates
        //property real speedWalk: 1 * mm * direction

        width: 5 * mm
        height: width
        color: "orange"
        anchors.bottom: parent.bottom

        function move(){
            if (x > parent.width - rect2.width)
                direction = -1

            if (x < 0)
                direction = 1

            x += speedWalk
        }
    }

    FrameAnimation {
        id: frameAnimation
        running: true
        property real smoothfps: smoothFrameTime > 0 ? (1.0 / smoothFrameTime) : 0
        property real fps: frameTime > 0 ? (1.0 / frameTime) : 0


        onTriggered: {
            rect2.move()
        }
    }

    //property real speedNormalized: rect.speed * frameAnimation.frameTime
    Text {
        id: name
        text: " frameTime: " + frameAnimation.frameTime
        + "\n smoothFrameTime: "+frameAnimation.smoothFrameTime
        + "\n smooth fps: " + frameAnimation.smoothfps.toFixed(0)
        + "\n fps: " + frameAnimation.fps.toFixed(0)
        + "\n rectangle velocity: " + rect2.speedWalk//.toFixed(3)
    }

    MouseArea {
        anchors.fill: parent
        onClicked: frameAnimation.running = !frameAnimation.running
    }
}

Anything else I should know about frames rates, so I dont get any more surprises with my game? What are some other good practices that I am not aware ? How do other games platforms like Unity handle the frames rates differences ?

SimonSchroeder

Your speedWalk is not just dependent of the frameTime, but also of the pixelDensity. So far, this seems to be correct to include both of these. However, you might have a higher resolution monitor now instead of just having a faster one. Are you using a scaling factor (its a setting of your operating system)? You should also include Screen.devicePixelRatio. Not sure, if this is the actual problem.