For example, in cases where there are hair and shadows.
I want to completely confine the hair and shadows in the same mesh and set the automatic weights with bones to work as comfortably as possible.
However, as shown below, if they are different in size, there is also a difference in the size of the square.
And the mesh cannot go beyond that rectangle. Why is it restricted like this?
The convenience regarding weights, meshes, etc., is so limited that I feel like kneeling down and crying... It might just be because I'm a beginner, though.
Copying a mesh outside of an image
qwer As you said, you cannot set the mesh hull beyond the boundaries of the original image. Therefore, in a case like the one you mentioned, you should set more padding when exporting the images using scripts, or use layer masks to match the size of the image (though this is only available in PhotoshopToSpine).
The reason for this restriction can only be answered by Nate, but my personal guess is that allowing vertex placement without regard to image boundaries would make the texture packing process too complicated.
For your information, even if the images used in your skeleton have a lot of whitespace, you can remove it when packing the texture if you enable Strip whitespace X/Y in the Texture Packer settings. This will ensure that the extra whitespace will not be a problem in the final packed texture atlas. Therefore, it is a good idea to keep the image with a sufficient amount of padding when you export it from the image editor, to allow for more freedom in the positioning of the mesh vertices.
This is how texture UVs work in hardware accelerated graphics (not just Spine). When Deformed is unchecked, you are setting the UV coordinates for each mesh vertex. The UVs are a location within the texture and therefore cannot be outside of the texture. Adding padding is the only solution. With polygon packing the whitespace outside the mesh hull won't take up any extra space.
Is it not possible to map a 1x1 transparent pixel to a polygon confirmed to be completely empty?
I'm also a small user who says, "This is inconvenient! How to improve it? I'm not sure..." but I would be happy to see this cool program named Spine improved to be more easily used in a wider range of cases.
It doesn't make sense for the task at hand. The task to setup UVs is, "where on the image do these vertices correspond". The answer cannot be "outside the image". If you want that, you need to make the image larger.
You can certainly create a mesh inside a 1x1 image, transparent or not.
If you exit Edit Mesh mode then you can move the vertices however you want. The restrictions come from being in Edit Mesh mode, which is where you define the UVs (where on the image each vertex corresponds).
I was short-sighted! If it's a transparent space, there's no problem in stretching it outside the Edit Mesh. Thank you.
Happy to help! 