Adjust fragment position

Unity Engine
, ,
1

I’m trying to offset back-facing triangles slightly to avoid z-fighting artifacts. bgolus has a good example here for doing the offset: Depth Test Offset in Shader Graph or something equivalent?

However, with the current version of Shader Graph the master stack looks like this:

9006742--1241407--upload_2023-5-11_14-28-57.png
9006742--1241407--upload_2023-5-11_14-28-57.png304×544 23 KB

A position input only exists for the vertex shader. There is no way to adjust the position in the fragment shader as far as I can tell.

But the “Is Front Face” check can only be done in the fragment shader. This makes sense, as without three vertices we don’t have a face yet.

So, is there a way to adjust fragment position in shader graph?

9006742--1241407--upload_2023-5-11_14-28-57.png
9006742--1241407--upload_2023-5-11_14-28-57.png304×544 23 KB

2

Alternatively, the objects could be rendered in two passes, once with using front faces + no face offset, and once using back faces and with some offset. But I assume this is not possible with shader graph.

3

Hi, it’s impossible to connect “Is Front Face” node with position output in both old shader graph and current shader graph, because the calculation of position output is done in vertex shader.

I think what you need is the pixel depth offset in HDRP shader graph fragment stage.

2 Likes
4

In HDRP, you’d use PixelDepthOffset, to bring a pixel closer or further away from the camera. This is functionally equivalent to being able to output fragment depth (in addition to color) from a regular fragment shader.

However, as far as I’m aware this isn’t supported in either the Built-in pipeline or URP (for no good reason that I can think about, since you can still do this just fine by hand-writing the shader in both pipelines, just not when using ShaderGraph).

1 Like
5

Thank you for the answers. (I’m sorry for the late reply, I just got a notification mail now).

And I’m sorry for the lousy wording, I indeed wanted to change the depth and not the whole position.

I ended up rendering the according objects a second time with the RenderObjects renderer feature, using a handwritten shader, with hardcoded depth offset. I had to use the same material for all back faces, which ended up being ok.

1 Like
6

You can also try requesting “Pixel Depth Offset” feature for URP shader graph in 2023 Dev Blitz Day forum. At least you’ll get a response from devs compared to submitting ideas on roadmap.

1 Like
7

Thanks for the suggestion. It seems someone requested that already: Shader graph: SV_Depth output and vertex attributes

1 Like