Question HDRP Decal Mesh Draw Order

Meshes using the Decal material in HDRP do not have any obvious functionality that allows for them to be sorted. In its simplest form on HDRP/Lit (grass) with two mesh decals HDRP/Decal (sand and an i) using Unity's plane mesh:

The "Mesh Decal Depth Bias", has no impact because the meshes are drawn by camera distance. Does anything exist in HDRP's workflow that would allow me to control the draw order of these meshes without using decal projectors?

I can batch both meshes into a single mesh and use a texture array and two quads with a tiny height offset to force the draw order in theory but that would be my last resort solution.

 

I have the same issue. There really needs to be a "Decal" Surface Type on Materials that enables the Sorting Priority found on Transparent materials. This is very much needed (as is an opacity just *just* ambient occlusion in the decal shader) for them to be useful for us.

I feel like this is another case of if Unity was making an actual game, they'd have run into these issues already and fixed them...

 

I'm not familiar with HDRP, but in URP you can create Decal Shader Graphs which have the Priority slider, ..maybe it works for HDRP as well ?

 

Thanks for the suggestion @polemical, but HDRP doesn't have that setting. Here's what it has:

• Draw Order - This is only for projectors for some reason!?!?

I tried it just to see, but it has no effect on two plane quads with different decal materials using different Draw Order values. Mesh Decal Bias/ Depth/ View also do nothing useful for this case.

So Unity, can we please get priority sorting in HDRP similar to URP for mesh-based decals? I see no reason this can't use the same "Draw Order" value (or rename it to Priority to match URP).

They'd should also be secondarily sorted (or just guaranteed) by their sub-mesh index. We have multiple submeshes using the same decal material (this is on a large terrain) so that they are culled spatially. We need to ensure that the draw sorting sorts by material Draw Order (Prioirty) first and then by sub mesh index otherwise the overlapping decals will pop/switch order as the camera moves.

 

I'd also like to point out that there is also no stable sort/draw order between GameObjects using the same material. So based on the camera location, decals will pop and randomly draw on top of one another if they overlap.

Can we please get a way to sort decal meshes and sub-meshes with a stable sort comparison so this doesn't happen? We use a lot of mesh decals and without a fix for this, we would not be able to ship. So ideally something along the lines of:
Material Priority > Shader > Material >Mesh > Sub Mesh Index > Mesh Renderer

 

Thanks @SebLagarde. Does this also fix sorting issues for decals using the same material in different GameObjects or sub-meshes of the same GameObject? If not, we still need an option for this otherwise all our terrain decals pop/change order as the camera moves.

 

@SebLagarde Ok, as long as it's stable down to the sub-mesh then it should work for us. Thanks for fixing it!

 

you can also, instance your own materials:

Code (CSharp):

1. using UnityEngine.Rendering.HighDefinition;
2.  
3. Material decalMaterial = GameObject.GetComponent<DecalProjector>().material;//get material
4. Material instanceMaterial = new Material(decalMaterial);//instance new (lone) material
5. GameObject.GetComponent<DecalProjector>().material = instanceMaterial;//set new material

then directly set the draw order by using

GameObject.GetComponent<DecalProjector>().material.SetInt("_DrawOrder", int)