Whilst tidying up my desk area I stumbled on an old George-bot (CGL CompuRobot) that I’d bought cheap on ebay some years ago. The electronics all work perfectly well, but a broken gear/cog means one of the wheels is undrivable. Eventually I may find a replacement gear, but in the meantime here are some photos showing some robust 1980s electronics.
George / CompuRobot CGL – Front View
George / CompuRobot CGL – Front View
George / CompuRobot CGL – Inside Front View
George / CompuRobot CGL – Motors View
George / CompuRobot CGL – Cogs, Gears and Differential Drive View
George / CompuRobot CGL – PCB Circuit View
George / CompuRobot CGL – Membrane Keypad PCB View
I had initially started development using Android and OpenGL ES using straightforward Java. But quickly ran into responsiveness issues due to naive use of Collections and the automatic garbage collector. After reading around the subject I stumbled onto libGDX (as mentioned in the previous post) and decided to start afresh. The library as a whole I found to be very straightforward to use. Great tools for setting up the initial projects. Excellent and expansive documentation for the API and cookbooks for actually making use of the library in your own application.
The result is a 2D game inspired by the arcade games played in my youth – The likes of Space Invaders, Silkworm and Missile Command to name a few.
PlanetKillers In-Game Screenshot
The general concept is a sort of steampunk or more Wellsian-era battle of primitive weaponry versus vastly superior technology. “Bows and arrows against the lightning!”. You are in control of a train (Class A4 inspired) racing across the country whilst using the artillery cannon to shoot the aliens before they bomb you or make it to the other side of the screen.
All of the graphics and sprites were drawn using InkScape – a free vector graphics package. Although they were loaded into the game as PNGs (with alpha). This gives some future proofing for devices with much greater resolution screens. Ideally there would be a nice way to render SVG images directly in-game.
The libGDX setup tools produce everything you need to get started provided you have already installed the Eclipse IDE (with the ADT plugins and Android SDKs). The tutorials again are top-notch. The game can be executed as a desktop application, an Android application, a browser application or if you have suitable tools as an iOS application.
The resultant game is quite snappy, although there are still areas that can be better optimised (to make better use of the libGDX library) and optimise the graphics to be device resolution-specific.
The AI might also be a little too hard too soon for some lesser-skilled players. See how you get on.
I have been wanting to get back into developing simple arcade games for the last few years. With modern mobile devices packing some serious processing power it seemed like a good time to start again. Back then it was all C++ and desktop Windows PCs using OpenGL or DirectX (or even better Irrlicht). Now, I wanted to focus on Android devices so Java and OpenGL ES were the obvious choice. To get my head back in the game (so to speak) I knocked up a simple invaders clone. The aim being to familiarise myself with OpenGL, user input options, and the performance capabilities of the devices.
I was using OpenGL ES 1.1 (fixed pipeline) and producing the meshes in code.
Cube, Icosahedron, and sphere approximation. The Sphere is approximated by subdividing the faces of an Icosahedron and pushing out the new vertices to lie on the sphere surface. From these basic meshes we can construct some simple game objects.
The scene graph makes use of transform matrices to position, scale and rotate the meshes relative to the parent node.
Each game object has a global transform applied to it, and this also applies to the bounding sphere which is used for collision detection.
The user is able to move the artillery and fire on the alien ships. When a collision is detected the ship and shell are destroyed and removed from the field of play.
This is a relatively simple scenario, and the processing capability of the mobile device should be more than sufficient to handle it. However, I noticed some slow down in the frame rate when firing (and running collision detection). The slowdown wasn’t in the physics, or the collision algorithms, but actually in the Garbage Collector being called when Collections were being modified. In the past when I’d used C++ this wasn’t an issue, memory management is handled by the user. But with Java, the Garbage Collector is an automatic process. On searching for more information about this I stumbled on this presentation by Kactus Games that gave some great insights into Android Game Development.
On further research I stumbled on an excellent framework that takes the limitations of Java into account to allow developers to create games that will run not only on Android devices, but also on the desktop, in HTML5 browsers, and on iOS devices. LibGDX is definitely worth a look. The documentation, tutorials and example code are extensive and comprehensive. I’m now going back to the start to build a quick test game using this framework prior to experimenting with some novel ideas I have for a new game.
I was wondering what music to listen to whilst coding today and had a hankering for some 80s magic. It reminded me of the Weetabix tapes we had as kids. Luckily someone has kindly put the track listings online so I can rebuild the playlist.
The Christmas Tree is up. The artificial antique one (a Woolworths classic) this year as the live one shed all of its needles in the garden last winter and has only grown back about half of them. The heating is on and cosy. The Christmas Robot is merrily beep beep booping in the background. So it seems the festivities have begun in earnest. Here’s hoping you all have an enjoyable festive season catching up with loved ones and look forward to an exciting year in 2014! 😀
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