Applying a theme to your Chrome Dev Tools

I wanted to make the Chrome dev tools editor easier on the eyes so I had a look around to see if it was possible. Since the web tools UI is web based it seems easy to skin and there is a great eco system of themes available from which to choose from.

A great site to browse through is, although it seems some of the themes no longer render correctly perhaps to due breaking changes in Chrome. One relatively complete theme which did function correctly is chromegray so this is the one I kept.

It will need to be installed into the following directory if your on Windows:

C:\Users\%USERNAME%\appdata\local\Google\Chrome\User Data\Default\User StyleSheets

So you can run the following PowerShell command to get this installed directly.

Invoke-WebRequest -Uri "" -OutFile "C:\Users\$env:USERNAME\appdata\local\Google\Chrome\User Data\Default\User StyleSheets\Custom.css" 

As a result I have a flatter design and an easier on the eyes editor which reminds me more of sublime text.


I have to recommend giving it a go, the editor updates live with the new theme. If you don’t like it then its easy to find another one or remove the theme altogether.

Dependency Injection in Scala and Play! using the cake pattern

It is my first time using Scala and I wanted a simple way to do DI so I could unit test my controller easily. The ability to use traits really seems to have a positive impact on code design, and enables things like DI to be quite easy without a runtime framework.

Real work scala dependency injection was a great introduction to implementing the Cake pattern in Scala so I won’t repeat the specifics of it here.

In case you haven't come across it the Play! framework is a complete web framework for JVM languages.

Personally I did not want to override plays controller instantiation so things stayed simple and I kept a clean routes table.

# Routes
# This file defines all application routes (Higher priority routes first)
# ~~~~

POST    /:topic/:key          controllers.Application.send(topic: String, key: String)
GET     /:topic/:key          controllers.Application.get(topic: String, key: String, groupId: String)

The standard play pattern changes slightly with the controller which is split between two definitions. The first is the Application object which works with the play route and inherites the ApplicationController trait. It defines a message consumer to a real implementation which is going to connect to a Kafka cluster and it is this that we will want to mock when running our unit tests.

object Application extends ApplicationController {
  val messageConsumer = new KafkaMessageConsumer

Now we have the ApplicationController itself which contains the controller behaviour and inherits from a MessageConsumerComponent which is where it has access to a message consumer. The controller does not care how this is created and just uses it.

trait ApplicationController extends Controller with MessageConsumerComponent {

  def get(topic: String, key: String, groupId: String) = Action {
    this.messageConsumer.get(topic, key, groupId)

  def send(topic: String, key: String) = Action(parse.text) {
    request =>

      val body: String = request.body

      this.messageConsumer.send(topic, key, body)

      Ok("received: " + topic + ", " + key + "," + body)

The message consumer is implemented as a pair of traits, the first as the interface which can be mocked and the second which is used in the cake pattern.

trait MessageConsumer {
  def get(topic: String, key: String, groupId: String)
  def send(topic: String, key: String, message: String)

trait MessageConsumerComponent {

  val messageConsumer: MessageConsumer

  class KafkaMessageConsumer extends MessageConsumer  {
    def get(topic: String, key: String, groupId: String) { ... }
    def send(topic: String, key: String, message: String) { ... }

This MessageConsumerComponent defines a messageConsumer field which will be accessible by any classes which inherit from the trait and can be set to either the KafkaMessageConsumer or a mock object. That's all there is to this implementation, so let's take a look at how this is done in a unit test.

trait TestEnvironment extends MessageConsumerComponent with ApplicationController with Mockito
  val messageConsumer = mock[KafkaMessageConsumer]

class ApplicationSpec extends Specification with TestEnvironment {

  "getting by topic" should {

    "return list of messages" in {
      val result = this.get("topic","key","group")(FakeRequest())
      there was one(messageConsumer).get("topic", "key", "group")
      status(result) must beEqualTo(OK)

I've followed Jonas' example in using a TestEnvironment object, but to avoid creating an extra component for the Application my system under test is the TestEnvironment. It might be worth changing this later but to keep things simple I've chosen this way.

There were a further two implementations I came across which are here and here. You might prefer one of those implementations and they are worth a read.

I am new to Scala so if there are errors, design issues or a Scala faux pas please let me know!


Excluding jmxtools with SBT

If you are using Scala and SBT you might experience this problem. In particular I was referencing Apache Kafka and found it trying to resolve the jmxtools which has been removed from the maven repository.

It took me a while to find the syntax to exclude this from my build.sbt file, but here it is:

libraryDependencies ++= Seq(
  "org.apache.kafka" % "kafka_2.10" % "0.8.0" excludeAll(ExclusionRule(organization = "com.sun.jdmk"),
                                                         ExclusionRule(organization = "com.sun.jmx"))

For more information you can check out the SBT documentation here.

How we used the chrome dev tools to optimise our html5 game

We wanted to experiment and see whether we could build a simple cross platform game using the latest web tech. The idea was that it would run across the mobile platforms and be easy to develop using our existing skills and tools. So for some background we are using cocoonjs to hardware accelerate canvas drawing and melonjs which is an OSS game engine which is easy to run on cocoon.

Our initial attempt was running very smoothly at 60fps on our powerful desktop browsers, however I was getting half that on my Galaxy Nexus. Given how simple the game was we were concerned and looked to find out why. We are developing using Chrome Canary which has the latest developer tools within.

CPU Profile

This was the first place we looked to see what was happening.


The trace is telling us we spend a majority of our time rendering rather than executing game logic. The sprites we are drawing are basic and we’ve made them as small as possible so this was the first surprise.


The flame chart puts into perspective how much idle time we have on a desktop machine and that each frame is speedily rendered in approximately 5ms. Initially that sounded good but given the lack of complexity in our graphics this performance is extremely disappointing and is a good indicator as to why the a mobile device might be struggling.

It wasn’t enough to know what to fix yet and for that we used the Canvas Debugger.

Canvas Debugger

This is an experimental chrome feature which means you will need to manually enable it. I used the learningthreejs blog which has a good video explanation but if you prefer something more textual you can follow the guide at html5rocks.

With the ability to inspect each canvas call both at the API level and visually we could track down where we were losing the performance. Below is a gif animation of cycling through each draw call shown in the debugger:


And with that visual representation it has become quite obvious where the extra draw calls are coming from, the background gradient is a 1px wide repeating image! Ironically we chose to do it this way for performance thinking loading a smaller image would be lighter on resources.

We were able to easily fix this in the map editor and it resulted in a big reduction in draw calls.


The gif animation also highlights the draw call for each tile which is imported from the map editor and this could be a further avenue to investigate if we want to target even lower performance devices.


Each frame now takes between 2 and 3ms to complete and more importantly the draw portion of that has been greatly reduced. It only takes 1ms to render on the desktop and the game code is now visible in the profile.


These changes were not only enough to run the game at 60fps on our mobiles, but has allowed us to increase the animation and visual fidelity while keeping the frame rate smooth. If you are working with canvasses either for game development or visualisations like d3 I recommend you grab the latest chrome tools and give them a go.


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