#hwinterstellar

Hackweek - Thursday

This day was mostly spent debugging problems, and doing it in a stupid way. I think now the intense hacking is starting to get to me, and I am being inefficient.

I have been having problems that I've blamed on myself and my inability to get the math right - in particular I couldn't get the alpha sort to work as it should, things were behaving oddly.

Finally, I managed to figure out that the problem I was having was really an OpenGL issue: I wasn't handling my VAOs and VBOs correctly, and things got broken in ways that I thought looked like bad math.

I could have figured this out much sooner by using something like vogl or just thinking calmly about what I was seeing. Instead I've been changing things here and there and staring at a gdb prompt.

You'd think I would have learned this lesson by now, but to my defense it's been years since I wrote software in plain C, and years since I last wrote any 3D code at all.

VAOs and VBOs

So, the key insight that solved this for me was when I read that OpenGL 3.2+ core profile no longer allows you to use the default VAO, instead requiring that all VBO draw calls are wrapped in a VAO. When I just started out I created two different concepts, one I called mesh which wrapped a VBO for vertex data and an optional VBO for index data, and one I called renderable which wrapped a VAO. When I then started rendering chunks, I never actually created any renderables, I just created meshes and called glDrawArrays directly.

Unfortunately, this worked. Sort of. Until I started rendering in passes.

Now I have merged these into a single mesh object which holds the VAO and VBOs.

Hackweek, wednesday

Yesterday I got stuck on collision detection. I have the Christer Ericson book but haven't read it in a long time, and clearly I've forgotten most of it. So today I decided to focus on something simpler, and implement lighting. I've got basic sunlight working now - no propagation yet, and the AO needs to flip some triangles to look good - I get artifacts seen above as described in this article. I'm not implementing that exact lighting algorithm, but the fix of flipping certain triangles should work for me too, I just need to implement it.