pixelmeat It is visible when the depth test is set to "Less Equal"
But it does not render as the opaque version when I change the test to "Greater"
Your yellow object seems to be fully in front. If you set it to Less Equal and see everything, setting it to Greater will show the inverse of everything, which is nothing 
. So I see nothing unexpected in these two screenshots.
Oh, maybe the screenshots' angle is misleading. The small yellow object is behind the big one. Here's a better angle:
It is visible when the depth test is set to "Less Equal"
Then which depth test did you set to Less Equal? If it's behind, it should not render with Less Equal, so something in your setup or the description is wrong.
Sorry to take a detour here, but I started getting this error:
Problematic material setup at Spine GameObject (blob_skeleton):
Warning: Premultiply-alpha atlas textures not supported in Linear color space!You can use a straight alpha texture with 'PMA Vertex Color' by choosing blend mode 'PMA Vertex, Straight Texture'.If you have a PMA Texture, please
a) re-export atlas as straight alpha texture with 'premultiply alpha' unchecked
(if you have already done this, please set the 'Straight Alpha Texture' Material parameter to 'true') or
b) switch to Gamma color space via
Project Settings - Player - Other Settings - Color Space.UnityEngine.Debug:LogWarningFormat (UnityEngine.Object,string,object[])
Spine.Unity.SkeletonRenderer:Initialize (bool,bool) (at Assets/Spine/Runtime/spine-unity/Components/SkeletonRenderer.cs:508)
Spine.Unity.SkeletonAnimation:Initialize (bool,bool) (at Assets/Spine/Runtime/spine-unity/Components/SkeletonAnimation.cs:189)
Spine.Unity.SkeletonRenderer:Awake () (at Assets/Spine/Runtime/spine-unity/Components/SkeletonRenderer.cs:402)
UnityEditor.EditorApplication:Internal_RestoreLastOpenedScenes ()
I don't think I can do viable tests until it is solved. What happened? I was just testing different shaders and selected this one:
Now the character won't render (I disabled all render features and filters to be sure)
It's just invisible. Its skeleton animation component is showing this warning:
I tried deleting the character files and reexporting/reimporting from Spine and the error persists. What did I just break?
pixelmeat As it says there, the error appears when a PMA texture is used in the material but your Unity project's color space is set to Linear. If it is your intention to use the PMA texture, set the Color Space to Gamma in the Player - Other Settings in Project Settings:
If exporting the textures as PMA itself is an error, uncheck Premultiply alpha in the Texture Packer settings in the Spine Editor and check Bleed instead. You will then be able to export straight alpha textures.
Misaki
I haven't touched the PMA option and it was checked (Is this the default?) Now I reexported the character without the PMA option.
I prefer not to change the color space of the project, as Linear is the default and I don't want to change values that I don't understand hehe.
Anyways, I reimported the NOT-PMA png to Unity and the error persists.
Here's the PNG, in case you need to check that it is NOT-PMA.
The warnings persist 
pixelmeat Ah, sorry my explanation was not complete. If the texture and material settings are not set appropriately for the Straight alpha texture, the error will not be resolved. See this section of the documentation for the correct settings:
Correct Texture Packer export and Texture and Material import settings
I haven't touched the PMA option and it was checked (Is this the default?)
Yes, the PMA option is enabled by default. This is because there are some advantages to using PMA textures.
Additive blend mode for skeleton slots.Misaki
Alright! Now I have configured the color space as Gamma and enabled PMA back. The warnings are gone and the character renders if I use the Spine/Skeleton shader.
But as soon as I change to the Universal Render Pipeline/Spine/Skeleton shader, the character disappears:
I still have the feeling that something broke in the background, as I had no issues with the Spine URP shaders before. Any ideas?
BTW, thanks so much for your help so far Misaki
pixelmeat I haven't touched the PMA option and it was checked (Is this the default?) Now I reexported the character without the PMA option.
Note that exporting as PMA was always wrong when using Linear color space then. The warning however will not lead to things not rendering at all, just rendering incorrectly with outline artifacts. If you see nothing, you've likely setup anything completely wrong with your graphics settings or Material settings, or something like that.
pixelmeat I prefer not to change the color space of the project, as Linear is the default and I don't want to change values that I don't understand hehe.
If you leave settings at Linear color space, semi-transparent colors will add up differently than what you're used to in Photoshop or other image editors.
pixelmeat Here's the PNG, in case you need to check that it is NOT-PMA.
It's impossible to check this png image. An object with a black outline and bleed will look pretty much identical. If you had no black outline, then you've exported it incorrectly.
pixelmeat I still have the feeling that something broke in the background, as I had no issues with the Spine URP shaders before. Any ideas?
If you see nothing at all, you've likely messed up your material settings, or any graphics settings in the Project Settings or your Render Pipeline Asset, or with your post-processing settings, etc.
Best revert to an older state in your version control history before performing the breaking changes. If you don't use any version control software, well, we can just recommend to undo the changes that you've made, and use version control software in the future.
@pixelmeat And note that the Universal Render Pipeline/Spine/Skeleton shader is for use with URP without a 2D Renderer, while Universal Render Pipeline/2D/Spine/Skeleton is for URP when using a 2D Renderer.
See the documentation here:
https://esotericsoftware.com/spine-unity-rendering#URP-Shaders-Extension-Package
Harald
Wow, I really didn't see that coming, the shaders were not working because I had reverted to the 2D renderer and I was still trying to use the 3D shaders. Changed to the 2D ones and it displays right now. I'll continue from here.
Just one more question for now. Are there versions of the outline shaders for the URP/2D category?
I mean like this one:
@pixelmeat Very glad to hear you've found the issue!
pixelmeat Just one more question for now. Are there versions of the outline shaders for the URP/2D category?
It's a bit more complicated currently, unfortunately there is no single-shader version available yet. This is planned in this issue ticket:
EsotericSoftware/spine-runtimes1824
However in the meantime you can use e.g. the RenderExistingMesh component and the Universal Render Pipeline/Spine/Outline/Skeleton-OutlineOnly shader as described here in the documentation.
You can find an outline URP example scene Outline Shaders URP.unity in the Samples of the Spine URP Shaders UPM package (installed via Package Manager under the Samples tab), there you can see this setup in action.
pixelmeat How can I make the outline object be mask-interactive?
By mask-interactive, do you mean the masks in the way of Inside-Mask Outside-Mask options of the Mask Interaction parameter of SkeletonAnimation? If so, that's the Stencil Comparison parameter (_StencilComp in the shader and in the Material properties under debug mode). Values are as follows (as names and parameter int-values):
Always, 8LessEqual, 4Greater, 5The integer values for each comparison operation can also be found under UnityEngine.Rendering.CompareFunction.
I have encountered a new problem now. My prototype is using custom axis sorting, so the scene sprites sort themselves using the Y axis instead of Z. All the characters and ground obstacles are in a sorting layer called onGround, more specifically in position 0 inside that sorting layer.
Now that the outline object is working, I need it to render in position 1, inside the onGround layer, so the "see through" silhouette will be visible when the character is behind an obstacle.
I've tried using the SortingGroup component, as I think this has worked for me in the past. Is that the right way to force a mesh to sort using the sprite sorting system? It is not working for me right now.
What do you think I am doing wrong?
Thanks!!
I can't delete my last post, so please ignore it. My mask was not in the wrong place. The setup is working as intended.
OK! Now I have something really similar to what I was trying to do. The problem is... I don't know why it's working! hahaha
Here's the effect in action:
The thing I'm not getting is why the shader that I use for the "silhouette" is working correctly inside the masks.
These are the shader settings:
There's no info there about Stencil Comparison, not even if I look in debug mode. So I don't know how is it working correctly with the Sprite Mask.
Here's the rest of the components I'm using to create the silhouette, based on the same components used in the outline method:
And that would be all for now, just looking for some enlightenment about why this is working before I happily move on 
Thanks!
