Implement a Texture2D to support Lottie animation

[beicause]

Related proposals:

• Add support for Lottie animation using ThorVG godot-proposals#9104

This implementation is simple and just works for me, by generating animation frame on-demand.

• Bugsquad edit, closes: Add support for Lottie animation using ThorVG godot-proposals#9104

[fire]

I'll put this on my list to review for the pipeline import.

[fire]

1. Run the godot engine binary with --doctool to update the documentation
2. I'll try to give you guidance for the "json" property being set as the default value

Here are the changes: beicause/godot@lottie...V-Sekai:godot:vsk-lottie-4.3

3. Thoughts on extending Ref<Image> directly? You could also extend Ref<Texture2D>.
4. There's a system to convert ".json" to "LottieSheet" that is missing that goes through the ResourceImporter.

[beicause]

Thanks for your guide.
I have changed it to inherit Texture2D. Now in editor it display Lottie normally, but when running the game it's empty. I don't find the reason.

[fire]

I was stuck, I suspect we need to use the resource importer system that takes json and gives a LottieTexture2D

[beicause]

I was stuck, I suspect we need to use the resource importer system that takes json and gives a LottieTexture2D

Don't open json directly. Create a LottieTexture2D and add the json as subresource.

[beicause]

I'm not very familiar with custom resource. I still can't understan why using code to set this texture works:

texture=LottieTexture2D.create_from_string(FileAccess.get_file_as_string("res://lottie.json"),1.0)

But setting the texture in editor doesn't work in games. ( Update: create_from_json doesn't work too. Fixed by disabling JSON::stringify sort_keys )

For resource importer, since lottie extension name is also .json and will be recognized as JSON, we have to customize one, for example .lottie. Or don't implement resource importer for Lottie, just create it manually and use JSON as property.

[fire]

So there's a way to create a resource importer plugin that scans for "*.json" as lottie.

I'll try to give you instructions as soon as I can or you can try it.

[Calinou]

This implementation is simple and just works for me, by generating animation frame on-demand.

While this is a simpler approach, note that it'll result in less smooth animations that no longer look crisp when zoomed in (e.g. due to Camera2D zoom or canvas_items stretch mode).

I think Lottie's biggest use case is that it allows for vector-based 2D animation with an arbitrary amount of frames (in other words, things can be freely interpolated). While you could choose to import at a high framerate (which doesn't seem to be adjustable in this importer right now), targeting 60 FPS will require a lot of memory.

This might be a dealbreaker for some use cases, so it's worth considering whether a true vector-based approach is more suitable first.

Performance is also an important caveat, similar to AnimatedTexture. Updating texture data often is slow, and it can also be inflexible (e.g. it might not obey pausing as expected).

On the bright side, this texture-based approach has some upsides, such as being easier to use in 3D (e.g. with Sprite3D). A vector-based solution wouldn't be usable in 3D unless rendered to a texture via ViewportTexture, in which case it would also lose its vector-based nature.

[beicause]

The common use case of Lottie is UI or other short duration animation, where AnimatedTexture is convenient. We can add a resource loader to import Lottie as AnimatedTexture
( I just find AnimatedTexture is deprecated, so it's not a good solution. )

[hermet]

Hello, Texture (or AnimatedTexture) methods have several advantages.

Primarily, GPU with direct drawing is not always good & faster since the following factors:

• When using Lottie as a static resource like SVG, or when animations are paused, the result from one rendering can be quickly reused in subsequent frames. This is particularly evident when using Lottie with UI assets that rarely change resolution.
• Lottie requires more composition steps than expected to complete a scene. This process involves using a temporary framebuffer to create intermediate scenes, and then extracting pixel information from the framebuffer for blending. These requirements can be quite burdensome on a GPU-based graphics pipeline compared to current software rendering & texturing method.
• Sometimes, the GPU might have too many burdens to complete real-time game graphics.

On the other hand, directly outputting vector drawings without going through textures can be more efficient in terms of memory use & performance in situations such as:

• Super high resolution for Lottie Scenes.
• Outputting very simple Lottie design resources (such as icons) without any composition.

Obviously it could be more beneficial to unify the vector drawing primitives as a single form in the Godot, however, implementing complex rendering logic like Lottie directly in Godot can be costly in terms of development resources and maintenance. Therefore, using third-party libraries may be advisable. In such architectures, typically using FBOs or textures can provide a stable integration structure during the main rendering and thorvg rendering.

Moving forward, ThorVG would be able to attempt hardware acceleration through its own hw rendering backend in order to integrate with Godot's main rendering pipeline, targeting FBOs for drawing. Nevertheless, if performance issues arise, attempting an aggressive integration structure based on direct drawing methods and sharing rendering contexts might be considered, although it will be comparatively challenging.

[beicause]

Godot editor gets stuck sometimes, especially when frame_count is high or there are multiple lottie files in the project, may because of ThorVG 0.13.2.
Tried ThorVG 0.12.10, it's stuck too, although less frequently.
Call stack:

[fire]

@beicause @hermet Is there a test project I can send to help ThorVG debug this?

[beicause]

@beicause @hermet Is there a test project I can send to help ThorVG debug this?

thorvg_test.zip

[hermet]

Hmm... it looks threading dead lock. let me review the patch first.

[hermet]

@beicause Could you please check the comments?

Also an opinion:
I just noticed that generating all frame images like this is quite intensive. I expect that dynamically updating the texture every frame by using ThorVG animation would be better for saving texture memory and reducing the harsh initialization bottleneck.

[beicause]

I think it's easier to use it in AnimationSprite2D/SpriteFrames by generating multiple frames at the same time. And if you just want one frame, you can set frame_count to 1 and set frame_begin. Playing the animation by dynamic updating the texture needs more codes for users.

Another option is implementing a import plugin to import Lottie as a image texture, like SVG. This avoids run-time cost, but increases app size.

[fire]

Another option is to treat this like theora like a video.

[beicause]

@hermet Hello, I made the change 6e56a6c according to your guidance, but still get stuck sometimes.

[hermet]

Thank you for your update. I have some additional feedback on your code, although it might not help to resolve this issue.

Unfortunately, I've tried similar calls with our ThorVG example with your attached resource(lottie.json in lottie_test.zip) using one extra thread but didn't encounter any issues, and even the thread sanitizer didn’t report anything.

I might need more context. Could you please conduct some tests and observe the results?

1. Disable the ThorVG threading feature and see the result:
   -> Remove #define THORVG_THREAD_SUPPORT in inc/config.h.
2. Does this worker thread seems not same with the thread which calls initialize_svg_module?
   
3. How many LottieTexture2D instances are created from this issue, and does update_image() calls are made just once per its instance?

[beicause]

@hermet
After disabling ThorVG thread support, I get in the infinite(?) loop in sw_engine/tvgSwRle.cpp static void _cubicTo(lines 665)
Sometimes it's OK, but sometimes the rc is very negative, I print it as follow:

Then I wait arc gradually decreasing, but rw.bezStack is (-1682252790473928, -1682252790480408), which is too negative and impassable to reach.

Additional info: In the same game project, the left successfully run, while the right is stuck, log diff:

[hermet]

@beicause It looks data corruption or overflow @_@. Could you please share me the size of picture here?

[beicause]

@beicause It looks data corruption or overflow @_@. Could you please share me the size of picture here?

The size of picture is correct and this call returns SUCCESS. _update_image is only called once at startup. It's strange that the render behavior is inconsistent ( not every time it gets stuck ).
I also try some other Lottie files, but don't reproduce the issue.