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For now, I'm basically just trying to understand some of the code behind the "drag and drop" sample in the Babylon.js playground. I would eventually like to create a 3d arcade style game, starting here by being able to move the meshes around WITHOUT the camera moving. But first things first tho, I need to understand the code thats here. I've read as much of the documentation and tutorials as I could, and I didn't see any previous post really related to what I'm looking for. There's are some things I dont get with the event listeners: getGroundPosition(), onPointerDown, onPointerMove. I altered the scene and added it to my hosting. I removed everything but the sphere. http://portfolio.blenderandgame.com/draganddrop.html Posting the code here, I commented the parts of the code I dont get: With getGroundPosition(), I dont get the predicate. Not sure i entirely grasp the concept of "predicate". I know that its a callback that returns a boolean value: returns true if ground was clicked. I just dont know what purpose that boolean serves. What other piece of code is that impacting? Not sure how it ties in. I notice that if you comment that part out, so that x and y are the only parameters, then the meshes will "sink" in into the ground instead of staying on the surface. I want to understand it on a code level tho. var getGroundPosition = function () { var pickinfo = scene.pick(scene.pointerX, scene.pointerY, function (mesh) { return mesh == ground; }); //?? dont understand purpose of predicate if (pickinfo.hit) { return pickinfo.pickedPoint; } return null; }I have the same question about the scene.pick predicate in onPointerDown (this one returns true if the ground was NOT what was clicked on. ) One OTHER question about this: startingPoint is assigned a value of getGroundPosition(evt). I know its passing the event. But getGroundPosition was defined WITHOUT parameters. So why is a parameter being passed to it? And what difference does that make? I've never seen an example like that with addEventListener. var onPointerDown = function (evt) { if (evt.button !== 0) { return; } var pickInfo = scene.pick(scene.pointerX, scene.pointerY, function (mesh) { return mesh !== ground; }); //dont understand purpose of predicate again if (pickInfo.hit) { currentMesh = pickInfo.pickedMesh; startingPoint = getGroundPosition(evt); //dont understand why argument is passed if fucntion was defined with no parameters.. if (startingPoint) { setTimeout(function () { camera.detachControl(canvas); }, 0); } } } Because of those two questions. There is a LOT I dont get about onPointerMove. But hopefully once I understand the above, it will help me figure out the rest. Dont want to bombard with my questions here on my first post Muchas Gracias to anyone that can help. Can't get any further with this and I dont want to give up and move on. Everything else I see with regard to movement is actually just moving the camera, not translating a mesh with a static camera view. This is the only sample I've come across that actually disengages the camera (at least only when the mesh is being moved).