Java Plugin Architecture 2016-10-16

In this post I will show how the plugin system in Chunky is being implemented.

Plugin support is surprisingly easy to add in a Java application thanks to the Java reflection API. Java reflection allows runtime type introspections, and dynamic code loading. Some of the more exotic uses cases for Java reflection is to generate executable code during runtime. A compiler hosted on and targeting the JVM could even use reflection for compile-time code execution. You don’t need to build anything nearly so exotic to implement a simple plugin system.

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The JavaFX Rewrite 2016-09-14

I have been working on rewriting the Chunky UI using JavaFX. After a few months of work I am nearly done with the rewrite and it has resulted in removing more than 7 thousand lines of code. That’s close to 15% of the total source code removed!

During the JavaFX rewrite i changed much more than just the UI code. In this post I will summarize the major things that I rewrote or refactored as part of the JavaFX rewrite.

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Categories: Chunky Programming

Project Updates 2016-08-17

I am home again from California, and my plants survived! This post is a collection of updates on some of my projects that I have posted about here on my blog before.


I have started coding on Chunky again, and I tried livestreaming some of my Chunky coding on Twitch. I streamed last evening from 20:00 to 24:00 CEST, and I’m planning to stream around the same time the rest of the week. Feel free to ask questions in the chat if you join my stream!

In Chunky I am working on the UI code, trying to finish up the new JavaFX UI. Here is a screenshot from last evening while I was working on a new Color Picker dialog:

Color Picker progress

My current Chunky development priorities are:

  1. Finish the new JavaFX UI.
  2. Add support for Minecraft 1.10 blocks.
  3. Add support for custom block models.
  4. Plugin system.


Plant Watering System

My automatic plant watering system was a success. My plants were completely alone in my apartment for about 5 weeks, and the watering system kept them alive. Here is the moisture graph from one of my plants:

Moisture - whole summer

I made a timelapse video of my plants using a Raspberry Pi camera. The video shows one image per day, taken at the same time of day, and the images cover about one and a half month of real time. My fiancée came home and moved the camera a bit at the end of the video.


As mentioned I was in California for work again this summer. Here are some pictures:

Golden Gate Bridge




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My thoughts on Virtual Reality 2016-08-14

I recently bought the HTC Vive, and after I converted my living room into a Virtual Reality cave I have been trying out lots of VR experiences.

The best thing about the Vive is that it has a very accurate motion tracking system for the head mounted display and the motion controllers. The most impressive game I tried so far is a bow-and-arrow minigame in Valve’s The Lab. In the game you are tasked with defending a gate from oncoming attacker stick figures by using a bow and arrow. You pick the bow in one hand and hold an arrow in your other hand. It feels very intuitive to shoot arrows using the virtual bow, and I became very immersed in the game feeling like I was almost there in the virtual game world.

The Lab - Image from Steam Store

Too little content

Sadly most of the games available for the Vive so far have very little content. Two of the best paid games available now are Space Pirate Trainer and Hover Junkers, but neither of them has much to offer in terms of gameplay. In Space Pirate Trainer you stand on a platform shooting flying robots that attack in waves – there is no enemy variety and you play on the same stationary platform with no other levels available, so even though the shooting action is cool it does get boring quickly. Hover Junkers does not have much more content – it similarly has a mode where you shoot flying robots attacking in waves, with slightly more enemy variety, there is also a mode where you fly around a small arena shooting at other players in a multiplayer death match.

I was very excited about trying racing and flying games in VR. It seemed like the perfect fit for the platform – ideally the VR features would just make it more immersive. So far there seem to be very few racing games with VR support. Project Cars is one game, and DiRT Rally another (for the Oculus Rift). I tried Project Cars and it made me slightly motion sick after a few races. It also has a problem keeping a high framerate, which I’ve noticed is very important for reducing motion sickness and keeping immersion. I think VR might work much better with slower paced driving games like Euro Truck Simulator 2, since it probably won’t make you motion sick as quickly.

Graphics, framerate, latency

Having high fidelity graphics does not seem at all important for VR immersion. The stereoscopic graphics make everything seem real, even if the textures have very low resolution or even if the 3D models have few polygons. High and consistent framerate and low latency matters much more for VR immersion. As soon as the framerate dips you instantly notice it, and worst of all it can make you feel motion sick. Latency is equally important – while looking around in VR it is very easy to notice the delay between your head movement and the world rotating around you. The Vive seems to handle motion tracking latency just about right, making the latency unnoticeable – at least to me – when the game I’m playing is running smoothly. It is similarly important to have fast tracking and low latency visualization of the motion controllers. When everything is tracked with low latency I can really believe that I’m swinging a lightsaber in front of me.

Speaking of lightsabers, there is a free VR demo on Steam called Trials on Tatooine. The game is very short – about 5 minutes – and has lots of framerate and latency problems. It seems like ILM tried to make it look very pretty before trying to make it run decently. During some short periods it ran okay, and the lightsaber felt very responsive and cool, but even though there is very little stuff happening on screen it still manages to tank the framerate and have terrible latency most of the time. Trials on Tatooine is an excellent example of how poor the experience gets when you sacrifice framerate and latency for graphics.

Trials on Tatooine

Creative tools

Tilt Brush is an interesting VR tool for painting in 3D, though painting 3D lines does not seem very useful to me. I’d rather use something more like ZBrush to sculpt in VR. VR could be a huge win for authoring 3D content. The industry standard 3D modeling tools are, as far as I know, all limited to using 2D screens for drawing shapes – I can imagine that many new 3D modeling tools will be made specifically to exploit VR.

Vive’s Head Mounted Display

The Vive has a 2160×1200 pixel display – each eye seeing roughly 1080×1200 pixels. When I use the display there is noticeable blurring when I look up or down, outside the center of the eyepieces. It’s also surprising how few pixels make out distant objects. The first times I used the HMD I felt like I had become short-sighted because I couldn’t make out distant objects clearly – it was simply because there are not enough pixels for faraway things.

There is also an effect that people describe as the “Screen Door” – it’s like a slight mesh pattern in your vision caused by the pixel grids in the display. I got used to that very quickly, and it really doesn’t detract that much from the experience. A more noticeable effect of the pixel grid is very pronounced false chromatic abberation from the pixel geometry of the display. The effect is not noticeable in the center of vision but quite noticeable near the edges of my vision where the lens blurring enhances it.

All in all, things that are reasonably close and near my viewing direction are rendered very nicely. I have not tried the Oculus Rift so I can’t say how the displays compare.

Developing for VR

I’ve become interested in coding something for the HTC Vive now that I’ve tried some of the existing games. I’m not entirely sure what I’d make yet, but one idea was to make some kind of VR exploration tool for Minecraft. It would be very cool to be able to fly around a Minecraft world in VR.


VR is very cool, but it’s overpriced and there are too few games for it right now.

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My thoughts on Gradle 2016-06-20

A while ago I wrote about why I prefer short build scripts and I briefly mentioned Gradle, a build system for Java. Today I’d like to share more of my thoughts on Gradle. I’ve been using it for most of my projects in the last couple of years. I wanted to summarize my thoughts here both for personal reflection and future reference, and hopefully I’ll help you decide if you want to use Gradle too.

I’ll mostly be comparing Gradle to two other build systems for Java: Ant and Maven. From personal experience these are the two most common build systems for Open Source Java projects. It seems like Maven is more common nowadays, but Ant used to be the de facto standard for building Java projects. I think Gradle is growing in popularity, especially since it is part of the official Android toolchain.

Things I like about Gradle

I have mostly positive things to say about Gradle, but I also have some complaints or nits that I think could be improved. Let’s start with the stuff I like in Gradle.

Goodbye XML

My favorite feature of Gradle is that it uses Groovy as the language for build scripts. Java build systems have a long tradition of XML-based build scripts (Ant & Maven), and I’m incredibly happy to use something that is not XML-based. XML may be nice for technical reasons but it sucks so bad to hand-write XML.

Thanks to being Groovy-based, Gradle has a nice and sparse syntax and it is even possible to write general purpose Groovy code inside the build script, allowing complex actions and decisions to be integrated in the build.

General purpose code in the build

Writing general purpose code in the build script is very useful because it allows adding any of the following complex high-level behaviors to the build:

  • Complex one-off project-specific build tasks.
  • Complex up-to-date checks for build tasks.
  • Environment-dependent build configuration.

Gradle makes it very simple to construct custom build tasks, making it easy to handle build steps that there may not already exist a plugin for. In comparison, you’d have to write your own one-off plugin to do something similar with Ant or Maven, a much larger investment for something that you’ll likely only use for one project.

Custom up-to-date checks are very useful for making a build more incremental. Gradle already has nicer incremental build support and improved dependency handling compared to Ant, but when using custom build tasks it may be useful to write your own up-to-date checks to decide when a rebuild is necessary in order to maximize incrementality.

Finally, I mentioned environment-dependent build configuration. This is more of a niche use case but one that I have found very useful in my projects. I usually generate version names using git describe, which gives nice incremental version names for Git projects. To generate such version strings in Gradle I use a common snippet of general-purpose code that I add in my build scripts. It looks something like this (edited for brevity):

// Runs 'git describe' and returns the output as a string.
def getVersion() {
    def output = tryCommand(['git', 'describe'])
    // Update resource files...
    output.readLines()[0] // Return the first line of output.

project.version = getVersion()

The getVersion() function above runs git describe to generate a version string. The function also stores the version string in a property file and does some error handling in case the git describe command failed.

Build by convention

Build by convention is not a new idea. I believe the concept was popularized by Maven, and Gradle has adopted the same conventions. Briefly, the idea of build by convention is this: if source files are stored in standard directories then you do not have to configure them in the build script.

Java projects use the following conventions: Java source files are stored in src/main/java, and test files are stored in src/test/java. If you follow this convention you’ll only need to use the Java plugin in Gradle to set up a new Java project:

apply plugin: 'java'

That’s it, a complete build script for a simple Java project. Getting started with your next project should be at least this simple.

Maven dependencies

In my eyes the best thing Maven gave the Open Source Java community was the Maven Central Repository. It’s a database of Java libraries which can be downloaded by Maven when building a project. If you don’t want to keep large Jar files in your repository you can add dependencies to the Central Repository and rely on Maven to fetch the libraries when the project is built.

The Maven Central Repository became hugely popular for Open Source Java projects, with most projects favoring the Central Repository over storing libraries in their own source repository. Support for Maven dependencies has since spread to many other build systems that can build Java or Scala applications.

Gradle also supports Maven dependencies natively. With just a few extra lines in your build script you can build with a Maven library:

apply plugin: 'java'
apply plugin: 'maven'
repositories {
dependencies {
    test 'junit:junit:4.12'

The Maven Central Repository has become an invaluable tool for simplifying Open Source development, it reduces the manual work needed to set up a new project using Open Source libraries. Many useful plugins for Gradle itself are even hosted in the Central Repository.

I love using Maven dependencies in Gradle, and it really feels like I’ve emerged from the dark ages of using Ant into the glorious future of Java building with Gradle using Maven dependencies.

Build daemon

Since a few releases back, Gradle comes with a daemon that runs in the background – it’s like a little build server that runs on your machine and waits for build commands. The Gradle daemon is a huge win for Gradle users, because without it, Gradle has a pretty long cold-start time – very noticeable and somewhat annoying. When using the daemon my builds start instantly, and the build over all goes much faster!

Before the Gradle daemon was released my Ant builds used to be much faster than my Gradle builds, but now my Gradle builds are faster than my Ant builds.

Portable build

In 2014 I was collaborating remotely with a professor in Germany and implementing a demonstration compiler for a language feature which the professor had invented. I wrote the compiler in Java, using JastAdd, and I was working on Linux. The professor was working on Windows, and didn’t have Gradle installed.

When I sent my code to the professor so he could try it, I had to make it as simple as possible to compile and run the code to remove any friction and not waste his time. Gradle to the rescue! With Gradle you can generate scripts that bootstrap the build system on most Windows or Linux/Mac platforms. It worked flawlessly, and really helped in the collaboration.

These cross-platform bootstrap scripts are called wrapper scripts. They download Gradle and make it run and build your project. These wrapper scripts are excellent for sharing a project with people who may not have Gradle installed, or who may have an older version of Gradle that can’t build the project.

Things that could be improved

I do like Gradle a lot, but there are a couple issues that I think could be improved.

Obscured functionality

Although I’ve had some positive things to say about the brevity of Gradle build scripts above, I think the terseness can be problematic in some cases. The main issue I have with the way Gradle scripts work is that they hide very much of what’s going on under the surface. It takes a long time to grok what really happens, at least if you learn Gradle mostly by using it rather than by reading the documentation – my preferred way of stumbling my way through new tech.

One example of an obtuse construct is appending actions to a build task. For example, you could declare a build task like this:

task buildHouse << { doWork() }

Alternatively, you could accomplish the same thing like this:

task buildHouse {
    doLast { doWork() }

The second form explains much more about what is happening. The first form relies on you knowing what the << operator stands for. I quickly learned what it meant, but nonetheless there was a period where I thought << was a thing you always had to use. Later on I learned that there existed doLast and when I knew that doLast existed, it was easy to discover doFirst.

Using default behavior is a double edged sword – it makes everything very compact and neat for the experienced user, but it hinders discoverability for new users.

Gradle hides a lot of other defaults under the surface. When you get started you don’t have a clue about what is really happening and often you don’t need to know, but when you want to start making more advanced build rules and defining your own up-to-date checks you really need to know what’s happening and in what order things are happening. One gotcha I learned is that anything enclosed in braces is a closure, and closures can be used to do lazy evaluation thereby solving some issues caused by inadvertently using configuration variables before they have been properly configured.

Learning more advanced Gradle usage and writing my own plugins felt needlessly difficult due to obscure semantics. Part of this obscurity is inherited from Groovy which in itself has some pretty complicated invisible behavior, such as the name lookup / delegation semantics.

Multiple configuration files

The main build script in Gradle is named build.gradle, but there are also two other files involved that you will have to edit them when you start making more advanced builds: settings.gradle,

It would be nice if everything project-specific could be consolidated into one file. Sometimes there is a need for non project specific configuration, but that should just require one extra file.

No implicit dependency on the build script

A minor issue I have with Gradle is that it does not track changes to the build script itself. If I edit a build task it would be reasonable to re-run that task on the next build, because the edits probably have affected the output of the build task.

Stupid logo

My last complaint is very non-technical and petty, but I think Gradle has a stupid logo. Gradle’s logo depicts an angry elephant. Why have an angry elephant as your logo when your motto is “Build happiness”? Gradle have even addressed the issue and noted that people will misunderstand this on their own blog, saying “You might find it a bit odd to see him swearing if our motto is ‘Build Happiness'”.

You are right it is odd, it doesn’t make sense. They go on to say that developers are often frustrated with their builds, and they call this phenomenon “Build Hell”, and the elephant is angry at Build Hell.

However, when I see that logo, I am reminded of unhappy moments caused by frustrating build problems. Do you want me to associate Gradle with Build Hell? You should want me to associate it with happiness. The elephant should be happy.

If you know that the logo is confusing, then the logo is bad. Logos must be as unconfusing as possible, otherwise they fail at their job of communicating your goals. Trying to be clever doesn’t work: if it’s not intuitive nobody gets your message.


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Categories: Programming

Automatic plant watering system 2016-05-16

I am away from home for three months. I wanted a way to ensure that two of my plants could survive while I was away, without a human watering them for a long time.

I built a small system to automate the plant watering process. Here is a picture of the system in action:

Waterbot Still

Some nice features of my watering system are:

  • Watering is done on a fixed schedule, but I can log in remotely to adjust the schedule.
  • Soil moisture is logged and moisture graphs are periodically generated.
  • A camera takes a picture of the watering system twice an hour.
  • Surveillance pictures and moisture graphs are uploaded to a website so I can easily check the status of the system.

Here are examples of the moisture graphs that my system generates:



The moisture graphs are generated using the R programming language and the excellent ggplot2 library. Here is a snippet of the code that generates one of the graphs above:

tod <- function(x) as.numeric(format(x, "%H")) + as.numeric(format(x, "%M"))/60
ggplot(moist, aes(x=time, y=m1)) + geom_point(aes(color=tod(time))) +
    scale_color_gradient(low='blue', high='orange') +
    labs(title='Plant 1', y='moisture')

One of the challenges of designing the watering system was that I had not done any hobby electronics projects before, so I had to learn a bit of electronics basics and refresh my memory from my undergrad electronics class.

Arduino and Raspberry

I used an Arduino Uno to prototype the water pump control. I had a lot of fun using the Arduino, and I ended up doing several other projects with Arduinos as well, such as reverse engineering an IR remote control for my home audio system.

The final watering system uses an Arduino to control a submersible water pump, and to measure soil moisture using two moisture sensing devices. The Arduino uses a USB serial port to listen for commands from a Raspberry Pi which has scripts that determine the watering schedule. This setup keeps the code on the Arduino really simple, and allows me to tweak a lot of the logic in the system by logging in to the Raspberry Pi via a remote shell. I could even reprogram the Arduino remotely if I wanted to.

The Raspberry Pi has a camera for taking the surveillance pictures. I’m planning to use the images from the camera to compile a time lapse video later on.

Here is a closeup of the box that sits on top of the water reservoir. It contains the Arduino and a prototype board with the power switching circuit for the pump:

Control Box


I have only one water pump that waters two separate plants. To make this work I have a regular garden hose divider to split the lab tubing and water both plants at the same time. I tweaked the length of the tubes that lead to the two plants to adjust the amount of water going to each plant. To make adjustments without drowning my plants I used plastic bags to collect the water while I was tweaking the system. Collecting the water in plastic bags let me measure exactly how much water each plant was receiving.

The current watering system is not flexible and relies on the two plants consuming relatively the same amount of water. If I decide to improve the watering system in the future I will probably install solenoid valves so that I can water each plant independently of the other. This would make the system more reliable for long-term use and make it possible to use a separate control loop for each plant.

Flooding concerns

Flooding was a big concern when I designed the system, so I placed each plant in a big plastic container large enough to collect all water in the reservoir in case a catastrophic failure should happen.

The towel under the water reservoir is there to catch condensation from the outside of the reservoir. I did not notice any condensation problems while the system was in trial mode before I left. Condensation could be a problem if the room temperature changes faster than the reservoir temperature. One other option I considered was to place the reservoir in another container like the one the big plant is standing in.

Future work

As mentioned, I would like to have individual plant watering using solenoid valves. This could also make the system modular – I could add extra plants to the water loop and have them individually watered just by adding an extra piece of tubing and a valve for each plant.

Another way of improving the system is to add moisture feedback in the control loop, and use e.g. a PID regulator to control the water pump. It is probably good to have oscillating moisture levels, at least that seems more natural for the plants, but I’d like a regulator that ensures that the three-day average moisture stays the same over a long time.

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