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Skeleton Clipping Documentation

Lucrecious

Hi,

I'm working on a runtime implementation for the Godot game engine, and it's going pretty well.

One thing I'm wondering about is the SkeletonClipping object.

I've looked through the API documentation and examples, but it's not clear to me how this works. I would really like an explanation. I kind of have sort of an idea from looking at its public methods and how it's used in the official runtimes but I'd like some concrete explanation.

Of course, I can just go in and copy the examples but that doesn't help me adapt the code when I need to.

From what I understand, the Clipping is applied directly to the immediate next (directly under) MeshAttachment or RegionAttachment. But if the next attachment is neither a MeshAttachment or RegionAttachment or another ClippingAttachment, then nothing is affected.

In the code, SkeletonClipping::clipEnd() is called if there's an error with the integration process or if the next attachment isn't Region, Mesh or Clipping.

But these are just my guesses. Would anyone be able to confirm how Clipping is actually done with the spine runtimes please?

Thanks

Lucrecious

Nate

A Godot runtime would be great to see! We have plans to support it ourselves, but have gotten bogged down lately with a number of other important things.

The user guide documentation is here:
Clipping - Spine User Guide
That describes how it works in the editor, but it translates well to the runtimes.

Clipping begins at the clipping attachment's slot. The attachment for each subsequent slot in the draw order is clipped until the clipping attachment end slot is reached (inclusive).

Note the clipEnd(slot) method in the Spine Runtimes code only ends clipping if the slot is the end slot. Clipping can be applied to multiple

Please note that if you include the official Spine Runtimes or adapt code from the Spine Runtimes, then you'd need to apply the Spine Runtimes License to your Godot runtime:
Spine Runtimes License Agreement
To be clear, in that case you'd not be able to apply the MIT License, which is the license what Godot uses. This may mean that the runtime would be best provided separately rather than as part of Godot, unless there is some way to make the difference in licensing clear.

Mario

Have a look at the spine-sfml runtime for reference. It demonstrates how to properly apply clipping attachments to the triangles of a region or mesh attachment.
spine-runtimes/spine-sfml.cpp at 3.8

Lucrecious

@Nate: Thanks Nate, I'll take a look at that documentation. I'm aware that I can't (or shouldn't) embed Godot with Spine due to licensing, however, this "plugin" is specifically made for my own project and the Godot editor will not be distributed along with it.

Maybe later on I'll put it up for the public once it's more polished and my game is released, but even then, I'd release it as a separate module that isn't distributed with the engine itself. There are also a few unofficial Spine modules already out there for Godot, but they didn't suit my needs; they're either over-complicated or oversimplified and lacked proper integration with the engine.

Thanks for the clarification 😃

@Mario: Thanks for the advice! I actually had taken an extensive look at the sfml runtime since it's simple and easy to follow. The problem is that the logic itself for the clipping is difficult to parse. I got the basic idea, and like I said, I could have just copied what the sfml runtime did, but I'm trying to best adapt the API to fit the engine, so it's best to know exactly how things work.

Mario

All clipping does is that it takes the triangles of a region (2 triangles) or mesh attachment (n triangles) and clips those triangles to the currently active clipping attachment, as seen here:
spine-runtimes/spine-sfml.cpp at 3.8

The Clipper is just some state the renderer retains, so we don't have to allocate scratch buffers every frame for the triangles coming out of the clipping process.