Asset importing

[nfagerlund]

OK, so assume I'm gonna keep working with these shaunjs sprites. Or, alternately, some other assets I get ahold of. That means I'm starting with (or can at least derive):

• Some number of animation frames, the same for each direction (can be derived from name)
• A per-frame pixel size (has to be derived from image resolution and frame count)

What I WANT to have is that, plus:

• Entity-consistent pivot coordinate, so you can transition smoothly between different animations without your body glitching around.
• Per-frame footbox
• Per-frame hitbox
• Per-frame hurtbox/attackbox
• Frames per second

...with all of the spatial ones measured in offsets from the bottom left corner, since that's the positioning origin.

The problem there is, all of those things are just, like, a social construct, maaannnnn. So I need some way to visually construct them in probably Aseprite, and then export them in a useful format that bevy can use.

So, uh,

• [x] Learn about what Aseprite can export
• [x] Mark up some sprites to play with
• [x] Learn about Bevy asset pipeline (and look into that aseprite importer)
• [x] (all the implementation work I already finished)
• [x] Make variant selection not take a String, that sucks. Do I need to keep freedom of custom tags that aren't obvious directions? Could always do an enum w/ eight non-data-carrying variants and one that has a String. And if I ever decide to do omnibus aseprite files (one per character/monster) or something, I'll need to seriously reconsider. Maybe just leave em strings for now, until profiling says don't?
• [x] deal with picking variants based on a single direction angle (rads) input. Need separate impls for 2, 3 (flip), 4, 5 (flip), 8 directions
• [x] angle-to-discrete-direction functions (req'd by ^^)
• [ ] Oh, and to support the prev., got to store memory of how many directions I have in a given animation struct.
• [x] Support both looping and non-looping animations
• [x] Emit signal of some kind when non-looping animation finishes?? need some way to transition controller states after doing Thing, effectively tying Thing's duration to the animation asset.
• [x] Assign origin & walkbox to entity, use in physics checks
• [ ] Special case for one-frame looping animations? (for static sprites like town npcs, don't bother animating but do have direction changes?)

[nfagerlund]

Okay, so I'm working with alpine-alpaca/asefile (rather than mdenchev/bevy_aseprite, which is too high-level for what I need).

Aseprite lets you link/reference cels for reduced storage overhead and easier updates of shared content. But it looks like the asefile crate abstracts over that, and presents you an interface that always returns full image content for each cel if you need to dig into pixels. Which is actually probably much nicer to work with! It's just highly redundant, especially since I need box content for every frame. Oh well! Importing can't be in the critical loop, then, but we already knew that.

Also, Cel has a magic .top_left() method that gets me exactly what I want, but it turns out that's an artifact of aseprite's pixel data compression/storage format. It must not be storing the transparent pixels that form the padding of a mostly-transparent cel, and instead just absolutely positioning the first meaningful pixel. So, there's no equivalent .bottom_right(). alas!!!

But, Cel.image().enumerate_pixels() pretty much gets me exactly what I need! The iterator yields the coords and rgba content as a (u32, u32, Rgba([u8; 4])), and if the fourth component of that Rgba is 0 it means it's a transparent pixel.

I just need to do that on every frame of the walkbox et al, and then associate the resulting rect bounds with the actual frame I'm working with. Oh... and also extract the visible image content I want and put it into some texture format bevy can use.

[nfagerlund]

• I'm going to want to iterate through the tags in the file to separate out the animations.
• whoa damn I can even get the frame timings.
• I think I can add every animated sprite cel to the same omnibus texture atlas. (Can't use .len() to count frames, but that's fine.)
• What all do I need, and where do I want to keep it?

[nfagerlund]

Can I annotate looped / not looped in the aseprite file? Does that make sense? Isaac says he never ended up needing animations that might be both looped and non-looped.

ETA: Ok nope, not today. https://community.aseprite.org/t/userdata-enhancements/4831/5 Noel from exok requested that exact same feature for the same reasons (ah hey, that's validating), and as of early 2022 it's planned but not started.

ETA: Well, the way tutorial boi did it was to handle it in the application code via the state machine and the "act out" trigger function. So even though loopiness probably does inhere in the animation, I'll just do that for now -- the easiest way I can see to tie it to the animation source would be a .meta.ase file or something, and that makes no sense until I have at least two things to put in there.

[nfagerlund]

OK, here we go, next move: refactor existing movement to use the same kinds of rectangles as the assets.

[nfagerlund]

Hmm so this is mostly done, the main thing is looping and emitting finished events.

[nfagerlund]

I did it!