var viewer = new Cesium.Viewer('cesiumContainer');

var scene = viewer.scene;

var canvas = viewer.canvas;

canvas.setAttribute('tabindex', '0'); // needed to put focus on the canvas

canvas.onclick = function() {

    canvas.focus();

};

var ellipsoid = viewer.scene.globe.ellipsoid;

// disable the default event handlers

scene.screenSpaceCameraController.enableRotate = false;

scene.screenSpaceCameraController.enableTranslate = false;

scene.screenSpaceCameraController.enableZoom = false;

scene.screenSpaceCameraController.enableTilt = false;

scene.screenSpaceCameraController.enableLook = false;

var startMousePosition;

var mousePosition;

var flags = {

    looking : false,

    moveForward : false,

    moveBackward : false,

    moveUp : false,

    moveDown : false,

    moveLeft : false,

    moveRight : false

};

var handler = new Cesium.ScreenSpaceEventHandler(canvas);

handler.setInputAction(function(movement) {

    flags.looking = true;

    mousePosition = startMousePosition = Cesium.Cartesian3.clone(movement.position);

}, Cesium.ScreenSpaceEventType.LEFT_DOWN);

handler.setInputAction(function(movement) {

    mousePosition = movement.endPosition;

}, Cesium.ScreenSpaceEventType.MOUSE_MOVE);

handler.setInputAction(function(position) {

    flags.looking = false;

}, Cesium.ScreenSpaceEventType.LEFT_UP);

function getFlagForKeyCode(keyCode) {

    switch (keyCode) {

    case 'W'.charCodeAt(0):

        return 'moveForward';

    case 'S'.charCodeAt(0):

        return 'moveBackward';

    case 'Q'.charCodeAt(0):

        return 'moveUp';

    case 'E'.charCodeAt(0):

        return 'moveDown';

    case 'D'.charCodeAt(0):

        return 'moveRight';

    case 'A'.charCodeAt(0):

        return 'moveLeft';

    default:

        return undefined;

    }

}

document.addEventListener('keydown', function(e) {

    var flagName = getFlagForKeyCode(e.keyCode);

    if (typeof flagName !== 'undefined') {

        flags[flagName] = true;

    }

}, false);

document.addEventListener('keyup', function(e) {

    var flagName = getFlagForKeyCode(e.keyCode);

    if (typeof flagName !== 'undefined') {

        flags[flagName] = false;

    }

}, false);

viewer.clock.onTick.addEventListener(function(clock) {

    var camera = viewer.camera;

    if (flags.looking) {

        var width = canvas.clientWidth;

        var height = canvas.clientHeight;

        // Coordinate (0.0, 0.0) will be where the mouse was clicked.

        var x = (mousePosition.x - startMousePosition.x) / width;

        var y = -(mousePosition.y - startMousePosition.y) / height;

        var lookFactor = 0.05;

        camera.lookRight(x * lookFactor);

        camera.lookUp(y * lookFactor);

    }

    // Change movement speed based on the distance of the camera to the surface of the ellipsoid.

    var cameraHeight = ellipsoid.cartesianToCartographic(camera.position).height;

    var moveRate = cameraHeight / 100.0;

    if (flags.moveForward) {

        camera.moveForward(moveRate);

    }

    if (flags.moveBackward) {

        camera.moveBackward(moveRate);

    }

    if (flags.moveUp) {

        camera.moveUp(moveRate);

    }

    if (flags.moveDown) {

        camera.moveDown(moveRate);

    }

    if (flags.moveLeft) {

        camera.moveLeft(moveRate);

    }

    if (flags.moveRight) {

        camera.moveRight(moveRate);

    }

});