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From one hand-pixeled isometric dev (https://store.steampowered.com/app/690370/Cantata/) to another, congrats!

People really discount the complexity of doing isometric — it's a surprisingly nuanced thing to implement, especially if you want inner-tile sorting/depth, tiles that occlude others, etc.

For sorting for me I ended up using geometry shaders with fixed layers to basically emit objects on top of each other and render everything in one pass. It makes things like the editor and runtime incredible fast, which looks like you did as well! Happy to see more games with this style, I think the look is unbeatable.

Thanks! Sorting whole sprites is definitely a complicated problem and it took some time to arrive at the solution I use today.

I noticed this bit in the article...

"Screenshots suggest cities more complex than suburban plots are possible in Metropolis 1998."

Which sounds good, but naturally, all such simulators bake in assumptions about what good urban planning is. These are the kinds that get rewarded by the simulator. SimCity bakes in the awful postwar fetish for suburban sprawl and rigid zoning, for example. Perhaps it isn't always done explicitly - game developers could very well be absorbing prevailing sensibilities and expectations about urban planning unwittingly, for example. Most people today think suburban sprawl is just a fact. They even find it desirable, as that is what they are expected to want or what they grew up with themselves.

What I would like to see is a simulator based on traditional principles of urban planning or the 15 minute neighborhood or whatever. This could have the benefit of stirring the imagination of future urban planners to look beyond broken postwar patterns.

(Side note: the Venice Biennale this year features more examples of sustainable architecture and green adaptations of existing buildings, which is a welcome change compared to the usual practice of the weird architecture Olympics where vain architects compete to maximize how bizarre they can make a building, which is not to say beautiful or useful.)

Yes.. but: Don't forget this is a game, and the main mission of a game is to be FUN.

Sure, but I think doing this would actually make it fun. The weird, inhuman assumptions SimCity and other simulators make, I argue, make those games less fun, because they leave you with a city that looks offensive. You're no longer managing or building a city with good vision in mind. You're just some boring manager operating within boring rules.

> Since sorting sprites is O(N^2),

You probably know this already but sorting is `N log(N)` in the general case but `N` when the range of values is known and relative small using pigeonhole sort [1]. That's probably what you're doing on the GPU.

[1]: https://en.wikipedia.org/wiki/Pigeonhole_sort

It's been 2-3 years since I've thought about this. I dug around and found an article that said the time complexity (for topological sorting of sprites) was O(N^2) [1]

It appears there are O(n log n) algorithms though, I just didnt come across them at the time :)

EDIT: Or maybe not! I dont have time to dig into this, but it may not be accurate enough

Im not sure that would work for my use case though, since you can see inside the buildings in my game (and there's see thru windows!). A bunch of high density buildings will be drawing tens of thousands of sprites within the camera's field of view.

For anyone who's interested, here's the scope of the problem:

Isometric projection is simulating a 3D world by layering 2D sprites in a specific order. Notably, units/vehicles in the game have smooth (floating point) movement, so they can be e.g. partially occluded by a wall or another object. My game also has pixel thin walls that can be placed on any edge of a tile.

So imagine sorting a vehicle sprite behind two wall sprites (the vehicle sprites are twice as wide) as it's moving across them. All you have are rectangles to work with. Now add in a stationary plant in front the wall, and a person walking in front of the plant, the two walls, and the vehicle.

e.g. There will be a time when the front the vehicle (the bottom of the rectangle sprite) is lower (i.e. closer to the camera) than a wall sprite, but the vehicle would still be occluded by the wall.

[1] https://mazebert.com/forum/news/isometric-depth-sorting--id7...

If you're happy with your engine's behavior and performance than feel free to disregard. But if it is something you want to noodle on...

> I dug around and found an article that said the time complexity (for topological sorting of sprites) was O(N^2)

Topo sort in general is O(V + E) where V is the number of vertices in the graph and E is the number of edges. If you consider your set of sprites a graph with an edge between every pair of sprites, then it does become O(N + N*N) which is O(N^2).

If the only way to get topo sort to work is by treating the sprites as a fully connected graph, then it's not the right approach. Topo sort really only makes sense when the number of edges between nodes is relatively low. You'd be better off using quicksort which is O(N log N).

However, since you are going to be resorting the same data each frame and most sprites stay in the same order, what you want is a sorting algorithm that works well on mostly-sorted data. In that case, I suspect insertion sort is what you want. It will roughly behave like O(N) when the data is mostly sorted.

Alternatively, you could look at bucket sort. While your sprites can be freely positioned with floating point coordinates (which makes pigeonhole sort a poor fit), they still fall within a known finite range, and bucket sort is designed to handle that case.

It's a fun problem to think about. [1] I don't have a computer science background, so I appreciate you bridging the gaps in my knowledge.

I mostly understand what you're suggesting (I'd need to read up on how each individual algorithm works at a low level). It's true that most of the sprites would remain in the same order and in theory it would be worth looking into this (it may benefit low powered machines -> widen the potential market).

However, there are other limitations with the framework I'm using that make me pause. I'm using OpenGL and Vertex Buffer Objects (semi-dynamic Vertex Arrays, ie. a std::vector<> of vertex information that the GPU can store locally). When a vertex array is updated, the entire array must be resent to the GPU, or alternatively one can do individual range updates (which... are not working at the moment). There can be so many sprites on the screen that a full update would cause the FPS to drop (learned this by example). And since CPU -> GPU communication is so costly, I assume hundreds of individual updates would also drop the FPS.

With my custom depth maps for each sprite, the vertex array only needs to be sent once. (Side note: the world is broken into 40x40 chunks)

> If the only way to get topo sort to work is by treating the sprites as a fully connected graph, then it's not the right approach.

One trick the OpenRCT devs did was split the screen (or scene?) into 64 pixel wide vertical strips. Though they still said the performance was O(N^2) for each strip.

[1] I am content with the engines performance for now. Last I tested I, a very dense scene ran >165 FPS on a medium performance GPU.

If you dont have twitter: https://old.reddit.com/r/Archapolis/comments/1o91vme/added_h...

Fun fact: the entire game is currently 27 MB

just got the demo, this is literally the smallest game in my collection. impressive

It's a lost art, but I for one appreciate when the developer makes the effort to avoid all the bloat that typically comes with new software these days (and especially games).

Agreed. Looking through my library, the only game remotely close is RoR1

I know this is probably super low on your priority list but any plans for a Linux port?

Ill be looking into porting after launch, so its possible!

> - Since sorting sprites is O(N^2), I figured out a way to create a depth map for each sprite to depth sort on the GPU

Could you elaborate on this some more? This seems very interesting.

See my other comment in this thread.

The solution I went for was drawing a 3D box (in 2D space, i.e. in the sprite sheet over each sprite), and then using that box to calculate the local depth within the "diamond"/isometric space is occupies (er, hope that makes sense!)

Have you investigated Unity’s “HPC#”? This is how you can write C++ in it. If you don’t even want to deal with ECS/DOTS.

I haven’t. One of the reasons I decided to write my own engine was to be able to organize the code/logic my way. I’m pretty sure I would have burnt out from the organizational friction of using eg unity

The art and little people walking around remind me of roller coaster tycoon. Very interesting looking game.