Can't get custom interpolators to work in a "Sprite Custom Lit" shader.

[JesperBHansen]

Hi,
I’m new to Shader Graphs, and URP, and I have had some problems getting a custom interpolator working with the Sprite Custom Lit" shader.

I have boiled the problem down to adding a interpolator to a Shader Graph based on “Sprite Custom Lit”.

If I attach a Vector3 (red color) directly to the “Base Color” of the fragment shader, the result is a (correct) red sprite, but if I attach the same Vector3 to an interpolator, and the interpolator to the “Base Color” I just get a black sprite.
The same experiment works fine with the “Unlit Sprite” base shader.

See screenshots for a better explanation

Unity: 2021.2.10f1
Universal RP: 12.1.4

[JesperBHansen]

I took a peek at the generated shader, and it seems like the interpolater is not sampled in the fragment shader, but instead float4(0,0,0,0) is in it’s place.

[laurentlavigne]

what i’m getting is a pixel interpollation, instead of triangle interpolation

maybe i’m not doing it right or custom interpolators aren’t supposed to behave the same as in unreal