Standard material have strange behavior with next pass materials

[atirut-w]

Godot version

v4.1.1.stable.official [bd6af8e]

System information

Godot v4.1.1.stable - Windows 10.0.22621 - Vulkan (Forward+) - dedicated AMD Radeon RX 6700 XT (Advanced Micro Devices, Inc.; 27.20.21034.37) - AMD Ryzen 7 5700X 8-Core Processor (16 Threads)

Issue description

If you set up a new material and its next pass, enabling these options will cause the first material to ignore the next pass:

• Emission
• Normal map
• Rim
• Clearcoat
• & many more

Even more strange, if I reopen the project, the behavior will change, sometimes always drawing over the next pass.

Steps to reproduce

1. Set up a mesh with a material with a non-default color.
2. Set up the material's next pass.
3. On the first material, enable any of the aforementioned option.

Minimal reproduction project

np.zip

[AThousandShips]

Can you please try with a supported version, like 4.1.2?

[atirut-w]

Sorry. I completely missed that version, somehow. I can reproduce it on 4.1.2 and even on the master branch.

2023-10-22.19-04-25.mp4

[jsjtxietian]

I did some more check, looks like toggle Emission will not cause this behaviour at master, but others do.

[clayjohn]

It looks like the material is just getting drawn over the next pass. Opaque objects are sorted by material, if you want to control their draw order (and ensure one is always drawn overtop, you need to adjust the render_priority setting.

In other words next_pass doesn't control draw order, render_priority does

[atirut-w]

That's.... very counter-intuitive...

[atirut-w]

I'm seeing the same behavior with material overlay. I think this is definitely a bug now:

2023-10-25.06-51-58.mp4

[jsjtxietian]

Opaque objects are sorted by material, if you want to control their draw order (and ensure one is always drawn overtop, you need to adjust the render_priority setting.

I suppose @atirut-w is confused at why next pass material will be drawn before base material given they have the same render priority? This is indeed very counter-intuitive.

[atirut-w]

I suppose @atirut-w is confused at why next pass material will be drawn before base material given they have the same render priority?

Basically this. By the way, check my latest comment. Material overlay also does not behave as expected

[clayjohn]

All opaque meshes are sorted by material for performance reasons. There is no guarantee of order except if you use render_priority. Material overlay works the same as next pass. It just inserts another draw call with that mesh using the chosen material.

To control draw order, you must use render_priority.

[atirut-w]

The behaviour should probably be noted in the docs, then.