Game Dev - Part 6

This week was spent doing a ton of stuff to support using an item from your inventory. Whilst this is a very basic gameplay mechanic, it's the first piece of real gameplay being integrated, so a lot of setup was required to get things architected properly.

Automated testing

Before proceeding with this, I explored doing automated render tests for the renderer. As future gameplay additions would require a lot of rendering code, I thought it'd be a good idea to get this stable and have a bit of code coverage.

Testing purely visual functionality is a bit strange, because it's not like you can just assert that OpenGL methods are called, you need to verify that they actually look correct too! This ruled out doing some kind of stubbing or basic "it called this method so it must be correct" style of testing.

Instead, I went with an approach I've used to great effect when doing automated tests for CSS styles - screenshot testing. The basic idea behind screenshot testing is you take a reference screenshot that demonstrates a correct visual state, then when the test runs, you get your UI into the correct state, then take a screenshot and diff the results.

The good thing about this is when the tests run it ensures pixel-perfect accuracy. If there are slight differences, say for example I accidentally swap red with blue when tinting a dialog box, it'll pick up on it and fail the test. The only downside is the space taken up in the git repository for the reference images. To mitigate this I made sure the outputs are very simple blocks of colour so they compress easily when saved as PNGs.

The results are very cool, as the diffing library I used will actually highlight the areas of the image that are incorrect, so you can see exactly what is wrong with the output. Here's a demo of all the tests I have so far:

Using items

The first step in getting the inventory working was to get item management in. This means being able to use an item, have the server acknowledge it, and update the UI to indicate the change in quantity. This also has to handle cases like removing an item from the inventory UI and shifting the following items back one slot.

This was mostly boilerplate and a bit of networking, and minor updates to the inventory UI Lua script to support shifting items around. Here's what it looks like:

Actually using items

Of course the above changes don't really achieve a working inventory, because nothing happens when you use an item. For that, I needed to get all of the scripting working, along with adding support for a bunch of extra messages between the client and server.

I spent a bit of time designing the logic flow between the client and server, it looks roughly like this:

A few essential item events were added to enable the kind of basic things you'd expect to happen when triggering events, e.g. locking player movement, displaying messages, etc. There was a lot of wiring up additional containers for player state on the server, and a fair bit of boilerplate for handling all of the extra messages sent between the client and the server.

Fortunately all of this stuff is reusable for other gameplay elements, which should help save time later.

Here's what the inventory looks like with scripting implemented:

This demonstrates tying together a bunch of the features I previously added, including the UI / Dialog system, localised text, and client/server scripting. It's very cool seeing it all be applied to something like this!


This week a ton of focus was placed on a single feature, which is a bit different to past weeks. I think this is mainly due to the fact that previous weeks were spent implementing a lot of core essentials to the engine, whereas this week was about using that functionality to build a gameplay feature, so the work was longer but more focused.

Next week the plan is to start implementing parts of the battle system. This will initially be focused on interacting with your ability deck, toggling on/off the battle UI, and displaying health and balance meters. With this in place, the engine will be set up nicely for participating in battles properly.

Til next time!