As I’ve been working on Devastro 2 I thought it would be great to be able to see and adjust properties of the in-game entities in the level editor.

Properties can be generic ones such as position, angle or color but there can also be ones specific only to certain types of objects – for example a “crate” object can have a (bool) property that defines if a pickup item should appear when the crate is broken. An enemy ship can have a property that defines how much damage it can take.

But how does the game know what types of objects have what properties? I guess we’ll need some kind of system for that.

A property system is a way to inspect and modify the properties of objects at runtime.

Implementing this is quite easy to do in languages such as Java or C# because reflection (aka introspection) is part of their runtimes. Also, custom annotations can be used to further describe how we want the properties to be published. But being the stubborn person I am, I’m writing this game in C++, so… how hard could it be? Maximum effort…

Use cases:

• Serialization – read/write properties to a file when saving and loading levels
• Editing – interactively adjust properties using sliders, checkboxes etc in a GUI.
• Debugging – inspect objects at runtime

We need to:

• Get a list of properties for each class in the game
• For each property, get its type, name and additional info for editing & serialization purposes
• For a given object instance, get/set the value of each property

I defined several constraints for the system:

• No custom preprocessing steps (looking at you, Qt)
• No macros
• Don’t use C++ RTTI
• Non-invasive – objects don’t need to register or add getters/setters; this is hard to avoid completely but currently there’s only 1 line of boilerplate declaration to be added to each class
• No runtime overhead for objects with properties (allow direct access to values when type is known)
• Simple setup (all properties for all objects defined in single location, DRY for subclasses)

And some compromises:

• OK to do string lookups but only when editing/loading, not in main game loop
• Limited set of property types (int/float/bool/string/enum)
• Limited amount of validation (can set a property to any value, object must deal with it; a value range can be defined as a hint for editor UI but is not enforced internally)

As of now the property system is up and running. Phew! I went through several iterations before settling on a design and it took a lot of effort to flesh it out for all the use cases and integrate it into the game.

Bottom line: Interesting challenge; looking forward to using Jai.

Another Blender practice session! This one took a few hours and I’m quite happy with the result.

It’s the house from the opening scene of Ed Wood.

I took two screenshots from the scene as the camera moves in towards the house.

I decided to do all my modeling based on those. I started by adding two cameras and attaching a screenshot to each of them using Blender’s “image empty” object.

Matching the camera views and the model to both screenshots at the same time was quite difficult. Matching the lighting was even harder since it’s a night scene with lightning effects.

Final result:

Reference shot #1 for comparison:

Subtle shadow mismatches show that my model isn’t 100% accurate, especially when it comes to depth. But let’s be honest, this is Ed Wood we’re talking about, so they probably had the lighting all wrong.

If I could devote any more time to this project I would probably model the terrain around the house a bit, add some trees, grass and dynamic lighting to match the movie scene. Also the texturing is pretty basic and not very accurate – another pass with manually painted details and wear & tear would be nice. Next time!

Here’s a concept render of a space scene with saucers approaching Earth. Inspired by the intro scene from Mars Attacks. I might use this in a video teaser for an upcoming game.

Kind of wishing I had known Blender when making Superforce… but there’s always next time!

Did a quick conversion of the Catnap Games logo into 3D and added a little animation.

Download hires version.

I just released a new app for the iPhone called Tiny Monitor. You can use it to quickly check if your website is up and running using the following rules:

• Page must contain a certain term
• Server response must have a certain status code (200 OK)
• Hostname must resolve to a certain IP address

Pull to refresh and get the current status. Tap the results to see what’s wrong.

First pass at a simple lowpoly machinegun:

Inspired by Devastro cover art:

The audio effects you get with OpenAL are:

• pitch
• pan
• gain
• that’s it

It’s a shame that OpenAL doesn’t provide more built-in effects or some equivalent of OpenGL’s shaders. HW accelerated or not – they could provide a lot of flexibility without having to rely on vendor-specific extensions.

With Superforce we had to make do with pitch shift where we really wanted a lowpass filter (in-game pause menu slows down the background music to 50%; this workaround actually turned out nice but lowpass or a combination of the two could have been even better). For the next game I decided to write my own audio mixer.

The actual sound mixing code turned out pretty well. Pitch shift was a bit tricky to get right. I also integrated the stb_vorbis decoder for streaming music. At first I was willing to keep using OpenAL as a backend since I already had it working. But OpenAL is a layer on top of Core Audio, so I couldn’t sleep well knowing that I could get rid of it…

So, Core Audio. With OpenAL, you play sounds. You can take your time. OpenAL will keep playing the sounds you already fired – no problem, no glitches. With Core Audio, it works the other way – you don’t call them, they call you. Like some sort of crime syndicate. And they will keep calling, whether you’re ready or not. You better be.

I got basic Core Audio output to work on the Mac pretty quickly but the setup wasn’t right. I was filling my mix buffer on the main thread and the Core Audio callback could come in to pick it up whenever it wanted. This was definitely going to cause problems when I’d start playing more sounds – sooner or later the callback was going to happen at a BAD TIME. Also, whenever the main thread got behind even a little bit during fullscreen transitions or loading, I could hear glitches – it didn’t fill the buffer quickly enough.

After a bit of research I settled on a more sophisticated approach. It is multithreaded and it gets me gapless playback even when loading a level or switching to fullscreen mode.

• MAIN THREAD (GAME LOOP) → PLAY SOUND 1 → PLAY SOUND 2 → VSYNC, RENDER → REPEAT
• MIXER THREAD → GET CURRENT SOUNDS → MIX INTO A FREE BUFFER → WAIT A BIT → REPEAT
• CORE AUDIO CALLBACK → GET A FULL BUFFER FROM MIXER → USE IT TO FILL CORE AUDIO BUFFER → RETURN

The threads communicate using lock-free queues.

• The game thread starts and stops sounds by sending commands into a lock-free queue.
• The mixer thread reads from that queue and updates its internal information; then it gets a new empty buffer and mixes the sounds into it. When the buffer is filled it is put on another lock-free queue.
• The Core Audio callback is called by the OS. It gets a full buffer from the buffer queue and just copies that into the destination Core Audio buffer. The size of the buffers coming from the mixer may differ from Core Audio, so it keeps a “cursor” inside the current source buffer.

There are several variables I can adjust:

• Buffer size (currently 512 samples, matching Core Audio)
• Buffer count (currently 3)
• Mixer thread update frequency (currently 100Hz)

The latency is ~30ms, which is about two frames at 60FPS. I think that’s fine. I should probably add another thread dedicated to reading audio streams from disk and decoding to avoid problems with slow disk access. Some people still have HDDs…

In general, I’m quite happy with this. Ironically, my new mixer can still do only pitch, pan and gain but I now have the option to write my own sound effects, because I control the whole thing.