Swift: get values from Accelerometer and Gyroscope via CMMotionManager

To access data from Accelerometer and Gyroscope we are going to use CMMotionManager.
Here’s the class what wraps everything related to motion API (CMMotionManager).
And here’s the code:
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swift: How to insert animated watermark into the video, or how to merge two videos

So I have a video from camera and array of images – result of screen capturing, basically the list of screenshots.
I want to merge them and add ability for User to save the resulted video on the phone. Let’s insert static image as a watermark as well as animated (video in video) watermark into the main video.

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Swift: how to record a screen video, or convert images to videos

Let say we want to capture the screen of your game and have it as a video in output.
Search results on “How to record screen video in swift” will lead us to RPScreenRecorder, it’s kind of cool, but for security reasons you are no allowed to save video or even access it. The only trick how to solve it is to make number of screenshots, save them as an array of Images. Unfortunately, you can deal with some performance issues here, it could be feasible to make like 30 fps capturing but it depends on many factors. For my game I came up with 30/5 fps, here’s the whole code:
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How to add pixel-perfect physics to an SKSpriteNode

To perfect the collision detection, basically to ignore transparency during the interest we can use SKPhysicsBody. The idea here is to have two images – one is what User sees, another is very simplified version for SpriteKit engine – simplified from color and geometry standpoint. The more complex “collision body” is the more resources it will spend during each frame to calculate collisions. Just for instance here’s the actual image and it’s “mask”

Now we are ready for some code
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Swift: how to get decibels

You might had a chance to check out the new trend – scream application. The most popular one I believe “Chicken Scream”. The new weird and funny interface for the games. Let’s take a look at how chicken scream works – the main part of functionality is to detect the background noice to set up the threshold, and to get “loudness” value – some how to measure the decibels.
In scope of my tests and investigations I’ve decided to create a flappy bird like game but where you need to scream, kind of flappy bird scream, you may want check out the result – “Scream to Fly” (appstore link, my site link)

All right, the first thing to start you need to request access to the mic, to have such ability we need to add the following to the Info.plist – click “plus” and start typing “Privacy – Microphone Usage Description” and add the value, something like – “Access to microphone is needed to detect noice level only.”. This message will appear when you request the access to it programmatically.

To check whether permissions were granted or to request ones you’ll need the following method:
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AWS DynamoDB query top 5 scores for country

Let’s take a look at how to query top 5 scores from AWS DynamoDB, let say we have some top scores table and want to get top 5 performers for the specific country. What we also need is not to waste the network resources, that’s why we will specify what exact fields we need to fetch from server – with help of projectionExpression.
Moreover let’s take a look at how to deal with the following error:
com.amazon.coral.validate#ValidationException”,”message”:”Invalid ProjectionExpression: Attribute name is a reserved keyword; reserved keyword: name”

it could be solved by adding reserved words to the expressionAttributeNames, e.g. instead of

queryExpression.projectionExpression = "userId,challenge,country,name,total"

where name and total are reserved words let’s do the following

queryExpression.expressionAttributeNames = [
            "#n": "name",
            "#t": "total",
queryExpression.projectionExpression = "userId,challenge,country,#n,#t"

That approach will eliminate the ValidationException – reserved keyword; reserved keyword error.

Here’s the whole method
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Swift: How to create iOS Today extension and share data with containing app

Do you happen had a chance to see the 3d touch icon widget or iOS Today Extension, let’s take a look at how to create an Extension in swift, how to open containing app and how to share data with containing app.

To add Today Extension to the project click “file” -> “new” -> “target”: chose “Today Extension”.
Let’s go to “Capabilities” tab and enable “App Groups” for both AppWithExtension and Extension targets, for both app and extension you need to click “+” icon under the “App Groups” and add Groups to you app id, e.g. like here

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Swift: how to use 3D Touch – Introduction

3D Touch or force touch – is a new feature that have been introduced in the iPhone 6s. It’s interesting to know that you can get touch force, it is a number from 0 up to 6.6667, actually it a number from 0 up to maximumPossibleForce.

Let’s take a look at how to check if 3d touch is supported on current device:

func is3dTouchAvailable(traitCollection: UITraitCollection) -> Bool {
    return traitCollection.forceTouchCapability == UIForceTouchCapability.available
// Let's call it somewhere from the GameScene for instance
override func didMove(to view: SKView) {
    if(is3dTouchAvailable(traitCollection: self.view!.traitCollection)) {

Feel free to take a look at the example project – I’ll provide the link in the end of this post.
So this is a good practice to check whether 3d touch is supported or not.

Here’s an example of how to get the force of the 3d touch

func touchMoved(touch: UITouch, toPoint pos: CGPoint) {
    let location = touch.location(in: self)
    let node = self.atPoint(location)
    if is3dTouchEnabled {
        bubble.setPressure(pressurePercent: touch.force / touch.maximumPossibleForce)
    } else {
        // It is important to use touchMoved for iPhones w/o 3dTouch,
        // So we can "emulate" it.
        bubble.setPressure(pressurePercent: 1)

The current value of the Touch’s force is touch.force and the touch.maximumPossibleForce is a good one to convert force value to the “percentage”.
This code is from the small example of how to “emulate” the bubble reacting on the force of the touch.
To try this on your iPhone 6s/7 you can install this bubble wrap app real quick.

Here is my previous post with more details about Haptic feedback.

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IoT: raspberry pi 3 how to blink led from iPhone

Internet of Things: raspberry pi 3 – how to blink led from iPhone?

Here’s a tech stack:
– raspberry pi 3 + led
– node-red hosted in AWS/anywhere – should be available in internet
– node js script on raspberry pi connected to node-red via web socket
– swift/ios app which makes http requests to node-red

Let’s start from node-red configuration (it’s a really cool tool for wiring together hardware devices, APIs and online services). All we need is to have “http GET” input, let specify the following path “/mmled/status” for it. and we want to wire it with Output/”Listen on” “web socket” with “/ws/mmled” path. We might also want to add “pay load” node.
So with several “debug” nodes (convenient way to debug our endpoint) it should look something like this:


At this point if we will GET https://{nore-red-host}/mmled/status?value=1 we will see the following things:
– {“value”: 1} in the debug panel
– the same message we will get in case if we are listening the “wss://{nore-red-host}/ws/mmled” socket.

Let’s check it, here is the node js “server” script which we going to start like “sudo node server” on raspberry pi:

var W3CWebSocket = require('websocket').w3cwebsocket;
var Gpio = require('onoff').Gpio;
var led = new Gpio(17, 'out');  
var client = new W3CWebSocket('wss://{node-red-host}/ws/mmled');
client.onerror = function() {
    console.log('Connection Error');
client.onopen = function() {
    console.log('WebSocket Client Connected');
client.onclose = function() {
    console.log('echo-protocol Client Closed');
    if (led) led.unexport();
client.onmessage = function(e) {
    if (typeof e.data === 'string') {
        console.log("Received: '" + e.data + "'");
        try {
            var data = JSON.parse(e.data);
            var newValue = parseInt(data.value);
            console.log('got new value = ' + newValue);
        } catch (ex) {
            console.log('invalid JSON in e.data');

Ok, let’s digg into the magic, first of all what is

var Gpio = require('onoff').Gpio;
var led = new Gpio(17, 'out');

if you will google “raspberry pi 3 pins” you’ll find where “GPIO 17” – you basically need to connect it to resistor + led + GND
after that you’ll have a chance to turn led on with this line – “led.writeSync(1);” and turn it off with “led.writeSync(0);“. So the circuit is the following:
raspberry pi [DPIO 17 pin] -> resistor -> led -> raspberry pi [GND pin]

Everything else we need to connect and listen socket and to react on the value change. run the script with

sudo node server

and try to GET https://{node-red-host}/mmled/status?value=1
and and try to GET https://{node-red-host}/mmled/status?value=0 to toggle the led. It’s awesome, at this step you can enable/disable your LED from internet!

Let’s create a new “single view” xcode project and drop a “switch” UI element on the view. Go to “Assistant editor” and bind the switch’s “action” to the code. Here is the controller’s code:

import UIKit
class ViewController: UIViewController {
    let ledUrl = "https://{node-red-host}/mmled/status"
    func setLed(status: Bool) {
        let finalUrl = ledUrl + "?value=" + (status ? "1" : "0")
        print("final url = " + finalUrl)
        let nsUrl = NSURL(string: finalUrl)
        let task = NSURLSession.sharedSession().dataTaskWithURL(nsUrl!) {(data, response, error) in
            print(NSString(data: data!, encoding: NSUTF8StringEncoding))
    @IBAction func onChange(sender: UISwitch) {
    override func viewDidLoad() {
        // Do any additional setup after loading the view, typically from a nib.
    override func didReceiveMemoryWarning() {
        // Dispose of any resources that can be recreated.

It’s just sending GET request with the value 1 or 0 on toggle/switch change. That’s it, if you’ll run the app and toggle the switch you’ll see the message in the “debug” node, and you’ll see your LED blinking which is Awesome! You might go further and replace led with relay+real lamp, but it’s a different story.

Here’s an EPIC demo video, just for fun and self-motivation.

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