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/*[[
    <Property name="cameraTarget" formalName="Camera Target" type="ObjectRef" default="Scene.Layer.Camera" description="Object in scene the camera should look at" />
    <Property name="startImmediately" formalName="Start Immediately?" type="Boolean" default="True" publishLevel="Advanced" description="Start immediately, or wait for\nthe Enable action to be called?" />

    <Handler name="start" formalName="Start" category="CameraLookAt" description="Begin looking the target" />
    <Handler name="stop" formalName="Stop" category="CameraLookAt" description="Stop looking the target" />
]]*/

import QtStudio3D.Behavior 1.0

Behavior {
    //External:
    property string cameraTarget
    property bool startImmediately
    //Internal:
    property bool running: false
    property var updateFunction

    function start() {
        running = true;
    }

    function stop() {
        running = false;
    }

    onInitialize: {
        if (startImmediately)
            start();
    }

    onUpdate: {
        if (!running)
            return;
        var targetTransform = calculateGlobalTransform(cameraTarget);
        var targetSpot = targetTransform.row(3).toVector3d();
        var cameraTransform = calculateGlobalTransform();
        var cameraSpot = cameraTransform.row(3).toVector3d();

        var matrix = calculateGlobalTransform("parent").inverted();
        matrix.m41 = 0;
        matrix.m42 = 0;
        matrix.m43 = 0;

        var rotateRay = targetSpot
                        .minus(cameraSpot)
                        .times(matrix);

        var rotation = lookAt(rotateRay);
        setAttributeVector("rotation", rotation);
    }

    function getAttributeVector(name) {
        var vec = Qt.vector3d(0, 0, 0);
        getAttribute(name + ".x", vec.x);
        getAttribute(name + ".y", vec.y);
        getAttribute(name + ".z", vec.z);
        return vec;
    }

    function setAttributeVector(name, vec) {
        setAttribute(name + ".x", vec.x);
        setAttribute(name + ".y", vec.y);
        setAttribute(name + ".z", vec.z);
    }
}
