Tell me more ×
Game Development Stack Exchange is a question and answer site for professional and independent game developers. It's 100% free, no registration required.
up vote 9 down vote favorite
2

I've been embracing Test-Driven Development (TDD) recently and it's had wonderful impacts on my development output and the resiliency of my codebase. I would like to extend this approach to some of the rendering work that I do in OpenGL, but I've been unable to find any good approaches to this.

I'll start with a concrete example so we know what kinds of things I want to test; lets say I want to create a unit cube that rotates about some axis, and that I want to ensure that, for some number of frames, each frame is rendered correctly.

How can I create an automated test case for this? Preferably, I'd even be able to write a test case before writing any code to render the cube (per usual TDD practices.) Among many other things, I'd want to make sure that the cube's size, location, and orientation are correct in each rendered frame. I may even want to make sure that the lighting equations in my shaders are correct in each frame.

The only remotely useful approach to this that I've come across involves comparing rendered output to a reference output, which generally precludes TDD practice, and is very cumbersome.

I could go on about other desired requirements, but I'm afraid the ones I've listed already are out of reach.

share|improve this question
3  
The entire problem here is that your test case is determined by a good output; but what happens if that output is buggy (false positive)? Either way I would start by checking wireframes first; then move to a forward-rendered scene and finally deferred (if you use that). You can XOR the entire image to make a quick comparison (entirely black passes). The GPU is really a bad area to apply TDD; but if you come up with anything smart I would love to know. – Jonathan Dickinson Jan 3 '12 at 21:01
I suspect that I won't get exactly the answer I hope for, but I still hope for some good ideas. Good thought on black pass. Testing the depth buffer could also be helpful. – stephelton Jan 3 '12 at 21:26
2  
@Adam thanks for sharing that. Unfortunately, it's way out of reach for an indie like me working on mobile games :) It also fails most of my basic requirements. – stephelton Jan 3 '12 at 22:10
@Adam you should definitely 'answerize' that link. Quite novel. – Jonathan Dickinson Jan 4 '12 at 9:12

2 Answers

up vote 7 down vote accepted

This seems like a good application of the Approval Tests framework or something like it.

As stated in the comments, you are still going to have an issue with false positives, if you happen to approve bad output, but this will at LEAST tell you when output has changed significantly.

Since you are using OpenGL, I'm assuming that approvals won't work for you directly, but the idea is sound. Just check the file hash and if it is different, show the failure in an appropriate diff viewer (like an image diff program). If you approve of the new version, update the "approved" file to match the new result.

share|improve this answer
That's an interesting tool. If you took something like the testing farm in Adam's link in the comments above, and applied an integrated approval mechanism like this, you'd probably start to approach something that is pretty low overhead. Thanks for sharing! – stephelton Jan 4 '12 at 6:29
up vote 1 down vote

I'm not into the game business, so please bear any potential stupid and naive perception

For me, writing tests that compare fully rendered images are not really unit tests, but full integration tests, because everything has to work fine for a successful test run.

What about an intermediate layer where you can check that everything is fine? There are two things that come to my mind:

  1. Don't draw directly, but issue a command stream that is turned into rendering calls down the way. The command stream can be checked for correctness. This is no end-to-end test, but you want unit tests, not full integration tests.

  2. This is really a variation on 1. Wrap OpenGL, catch all calls to it, strip this down to what you really want to test, and check if output still matches. The OpenGL wrapper can do the check itself if properly configured, and turns into a mock.

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.