It turns out I never used the close method in Restructure in any of my production code. This led to crashes cleaning up statements, as well as fully deleting the database. There was even a lone issue on GitHub pointing me to the problem, but I never fixed it for over 3 years.

Or Dance of the Sugar Plum Fairies?

Day 23 of Advent of Code had us simulate a group of elves spacing themselves out to plant fruit. This one is a little slapdash, but it’s still fun to look at. The ground and view could have been nicer, but the holidays always limit what I can attempt in a reasonable amount of time.

Day 12 of Advent of Code is a path finding problem, which is ripe for visualization. I used the A* algorithm for my solution, which should get to the closest path as fast as possible. It’s always crazy to watch these algorithms in action as they search and narrow down the solution near the end.

Lessons Learned

This is the first visualization with a large amount of nodes. For just the terrain, there are 5,904 nodes. The renderer uses one giant buffer for storing constants and allows a max of 3 renders in flight at a time. This means I can only use 1/3 of the buffer per render pass. In my original implementation, I was breaking past the 3MB buffer, which at best causes artifacts, and at worst causes slow downs and lock ups. To fix this, I added:

1. The ability to specify the buffer size at initialization.
2. A check after a render pass to fatally crash the app if more than the maximum buffer allowance is used.

Day 10 of Advent of Code had us determine which pixels should be enabled on a broken display. These pixels make a string that is the final input. Some times challenges like this can be interesting to look at, because the puzzle has the display go through a series of iterations before the string comes to form. This puzzle was much more straight forward.

Lessons Learned

My renderer never had a means to update the perspective matrix, leaving me stuck with a near / far ratio of 0.01 to 1000 and a field of view of 60º. I added updatePerspective to allow modification of these values at any time.

I noticed in my previous visualization that memory usage was extremely high. I didn’t think too much of this until this visualization also consumed a lot of memory for no real reason. This is a simple render comparatively. The last time this happened, I was bitten by CVMetalTextureCache taking a reference to the output texture as a parameter:

CVMetalTextureCacheCreateTextureFromImage(
    kCFAllocatorDefault, 
    textureCache, 
    pixelBuffer, 
    nil, 
    .bgra8Unorm, 
    CVPixelBufferGetWidth(pixelBuffer), 
    CVPixelBufferGetHeight(pixelBuffer), 
    0, 
    &tMetalTexture
)

In the above code, the function takes a reference to currentMetalTexture as output. This would cause Swift to never release any previous value in currentMetalTexture, effectively leaking every texture made. Assigning nil to currentMetalTexture was the fix in that case.

But this was not the issue. It felt like another texture leak, because the size was growing quickly with every frame. A look at the memory graph debug should 100,000+ allocations in Metal, so I was on the right track.

Most of the objects still in memory are piles of descriptors and other bookkeeping objects, but they were all stuck inside of autorelease pools. Since the rendering function is just one long async function, anything created inside of an autorelease pool in the function will never get released until the function eventually ends. Wrapping the function in an autoreleasepool closure solved the issue and brought memory consumption on both this visualization and the previous one under control.

Day 5 of Advent of Code revolves around a crane moving crates around to different stacks. This was a great opportunity to try my new 3D renderer for generating visualizations.

What Was Missed?

This was the first attempt at using the renderer, so a proper implementation was going to expose what features I didn’t know I needed.

Animation is a bit weird if you don’t have easing functions. I implemented a small set of functions on the 3D context, so that I can ease in and ease out animations as the crates go up, over, and down.

Rendering text was an easy implementation when using CoreGraphics and CoreText, but for 3D renderers, it gets more complex. I built a createTexture function that generates a CoreGraphics context of a given size, uses the given closure to let you draw as you need, and then converts that to a texture that is stored in the texture registry. There is a bit of overlap here with the 2D renderer, but for now, the utilities exist as copies between the two implementations.

Ooops!

There are a couple of rough edges if you manage to watch through the whole 1 hour video. I try not to rewrite too much of my original solution when I’m creating the visualized variant. I typically add the structures and logic from the initial project and slightly adapt it to work across both the console and visualized versions. Because of that, I’m typically stuck with weird state. If you watch the crates go up and over, they use the height of the tallest stack, even if that stack isn’t traversed. Crates travel further than they need to.

Also, because the movement is generated from a state when the moving crates are removed and not placed in their destination, you’ll some times see crates travel down through their own stack and move across at the wrong height. I’ll chalk that up to a quirk and leave it.