Does anyone know how to create "decals" like this in Godot4?

Audiobellum

It's a bit embarrassing to ask this but, does anyone know how to create "decals" like this in Godot4? I'm asking because I don't know how to get the Vulkan renderer on my laptop.😭

The dev that created this gave some clues as to how he did in the video description; they said "directspace intersect_point() method is used, final mesh is created with an arraymesh type". However, I'm still a beginner to Godot; I don't know what to do with that information. I'm been trying to research how to find a solution on my own but, this is taking up some much of time and interfering with with other other things I need to do. I understand that what I'm asking is for isn't super important and I've tried to move on by developing other aspects on my game but, I still can't get this thing out of my mind.
Could anyone provide me with pseudo code that could help me? If that's not too much to ask for, could you put me in the general direction of a solution?
If you can't do neither, could you me getting the Vulkan renderer working on my laptop so I can use the decal node in Godot? I haven't seen a lot of tutorials out there that can help me to get it down but, I've been embarrassed to ask about it because people talk about it as if it's one of those things everyone should already know how to do.

xyz

Audiobellum

Acquire PhysicsDirectSpaceState3D object by calling get_world_3d().get_direct_space_state() on any 3d node in your scene. This object lets you send direct intersection queries to the physics engine.
Use this object's method intersect_ray() to get the intersection point between your line of sight and any active collider in your scene. You'll need to pass in an argument of type PhysicsRayQueryParameters3D in which you have to set ray parameters representig your line of sight (from and to properties). You can also set other intersection parameters there, like collision masks and exclusions.
In the return results you will get intersection point and intersection normal. Instance the decal mesh, place it on intersection point and orient it to intersection normal using its look_at() method.

Audiobellum

xyz I do know how to use raycast with code; I'm mostly concerned about manipulating the shape of the mesh. I already have a system for placing the decal mesh down a spot when it's "shot", I'm just want to know how to manipulate the mesh so it's never too big on the surface it's on( making it look like a sticker).

Audiobellum

@"xyz"#p122446 Around the 45 second mark in the video, the shape of the mesh looked like it was changing shape though I don't know what that is. Is there anyway I can achieve that?

xyz

Audiobellum Looks like every decal mesh is created on the fly (using ArrayMesh), by projecting each quad vertex onto the collider. It's likely done by casting a ray from each vertex along initial decal normal, and then pushing that vertex towards the intersection point.

Audiobellum

xyz I suspect that the ArrayMesh was used in some way but, that concept has been hard for me to grasp despite reading about it in the documentation and even watching Youtube videos. Can you point to a beginner friendly tutorial on this subject? Alternatively, is there a way I can manipulate the vertices of an already existing mesh with code, as oppose to making the mesh with code? I think what's happening in the video, is that his mesh decals can detect when it's vertices are close to the surface of an object and then the modify themselves accordingly.

xyz

Audiobellum Don't know why you're confused about array mesh. Its usage is quite straightforward. You populate some arrays with vertex/face data and submit it to the mesh. There's all there is to it. The array mesh tutorial in the official documentation does a good job of explaining it, and there's a code example you can copy paste. Alternatively, you can edit an existing mesh using MeshDataTool. For simple meshes it's less bothersome to create them from scratch though. But submitting the mesh data is basically boilerplate. The "hard" part is figuring out projected vertex positions.

As for the exact projection method used in the video, I'm not 100% sure. It's very likely a hacky version of proper projected/clipped mesh decals, as there are some visible artifacts. I'm also not sure why the dev pointed out that intersect_point() was used. I'd expect it'd be based on raycasts. You can try to contact them and ask about specifics.

Audiobellum

xyz I think most of the challenges I have with the documentation have to do with my own personal struggle with ADHD but, since the tutorial is more about understanding how to use Godot as oppose to how to implement a specific feature in a particular game, I've become concerned about grasping the concepts as oppose to just following the tutorial; I think that's the challenge for me.

This post is going to be a slightly in-depth walk-through of me struggling to follow the tutorial in the Godot documentation about “Using the MeshDataTool”. This isn't a critique of the documentation as I'm aware that my mental issues could be getting in the way; I'm trying to put into perspective why I had a hard time following these tutorials.Here's a link to it here to put what I have to say about it in context:
https://docs.godotengine.org/en/stable/tutorials/3d/procedural_geometry/meshdatatool.html

I've already tried following the MeshDataTool in the documentation and I became fixated about why the functions have the names that they do as that would help me to grasp the concepts properly.

I'm about to show my ignorance about how the game engine works but, I naturally assume that the data from the mesh is already created if I can see the mesh from my MeshInstance3d in my viewport; this makes the function create_from_surface() sound confusing to me. This is perhaps a silly question but, what is being “created” by the function if the point of is to manipulate what's already there? I think I probably stepped into the tutorial with the wrong set of assumptions.

Now I can just follow the tutorial from back to forth without fulling grasping what I'm reading but, I fear that I would only learn how to follow the tutorial as oppose to using the information is a creative way to solve the problem I'm the decals I'm having.

The documentation also talks about a lot of 3d stuff that I've learned in Blender3d but, I've never known on to apply to programming in Godot. It's hard for me to focus on familiar sounding information that doesn't seem immediately relevant to what I'm trying to achieve but, that's no fault of the documentation.

I skimmed over that information but, it left me feeling a bit anxious as I probably missed out on some sort of important detail; this lead me to the part of the page that said “To access information from these arrays you use a function of the form get_****()”; think I understood the functions I saw underneath it; the function “mdt.get_vertex_count()” seemed like something I want to use as I do want to manipulate the positions of the mesh's vector.

After reading further, I see a statement I'm a bit confused about; it says “These modifications are not done in place on the ArrayMesh. If you are dynamically updating an existing ArrayMesh, first delete the existing surface before adding a new one using commit_to_surface()”.

I assume that what the statement means is that what's actually happening is the mesh is getting replaced with a modified version of itself. Hence this line of code underneath it:

mesh.clear_surfaces() # Deletes all of the mesh's surfaces.
mdt.commit_to_surface(mesh)

Still, I'm not sure if my interpretation of the statement was correct.

The tutorial ends with “a complete example that turns a spherical mesh called mesh into a randomly deformed blob complete with updated normals and vertex colors.”; it also ends with a link to a ArrayMesh tutorial.

xyz

Audiobellum MeshDataTool is an object that manipulates plain mesh data. It doesn't touch mesh resources directly. It holds its own copy of that data. To copy this data from an existing mesh resource into MeshDataTool's internal buffer, we use create_from_surface() method. After that, we can manipulate that copied data using MeshDataTool's various other methods. When we're finished, we copy that altered mesh data back into mesh resources(s) via commit_to_surface().

So you make a copy, alter that copy, and then copy back, overriding what was previously there.

Audiobellum

xyz So I made a function to test out using the MeshDataTool. Even though I think I'm starting to understand the concept, I ran into an error. Now even though I think I understand the error, I don't know how to fix it. Here's the function:

func mesh_manipulation_test():
	var mesh_editor = MeshDataTool.new() #mesh editor instantiated.
	mesh_editor.create_from_surface(mesh, 0) #placing copy of mesh data in mesh editor.
	mesh_editor.set_vertex(2, Vector3(0,5,0)) #Editing a vertex.
	mesh.clear_surfaces() #delete data from mesh.
	mesh_editor.commit_to_surface(mesh) #place edited data from mesh_editor into the mesh.

I got an error at the line that says "mesh.clear_surfaces()" because mesh doesn't have the function clear_surfaces(). What does have that function is an ArrayMesh, so I suspect that the line that says "mesh_editor.create_from_surface(mesh, 0)" and "mesh_editor.commit_to_surface(mesh)" have similar problems ( since mesh isn't a ArrayMesh). My goal is to edit an already existing mesh as to edit a mesh that was created with a ArrayMesh. I'm not sure what to do now.

xyz

Audiobellum What's the exact type of mesh then? If it's something other than ArrayMesh which is expected by the surface tool, you'll need to convert it to that type.

Audiobellum

xyz I'm using a quad mesh. How do I converting it?

xyz

Audiobellum QuadMesh is a procedural mesh, so you won't be able to change its vertices anyway. Here's what you can do

Get a copy of mesh data from quad mesh using ProceduralMesh::get_mesh_arrays()
Create a new array mesh object and assign acquired data to it using ArrayMesh::add_surface_from_arrays()

array_mesh.add_surface_from_arrays(Mesh.PRIMITIVE_TRIANGLES, quad_mesh.get_mesh_arrays())

Audiobellum

xyz Instead of trying to do the conversion, I tried following a video tutorial on how to create mesh with Godot 4. My code didn't seem to work but, I also didn't get any errors either. I did use the documentation for guidance, as I knew the video tutorial I was following was a bit outdated. Here's the video for reference:

The part of the documentation I was reading was titled "Using the ArrayMesh"; I read only the stuff that explained the use of the add_surface_to_arrays function. Here's a link to it for reference:

https://docs.godotengine.org/en/stable/tutorials/3d/procedural_geometry/arraymesh.html

So now here's what my code looks like:

@tool
extends MeshInstance3D


# Called when the node enters the scene tree for the first time.
func _ready():
	var mesh_data = []
	mesh_data.resize(ArrayMesh.ARRAY_VERTEX)
	mesh_data[ArrayMesh.ARRAY_VERTEX] = PackedVector3Array(
		[
			Vector3(0,0,0),
		Vector3(1,0,0),
		Vector3(1,1,0)
		]
	)
	mesh = ArrayMesh.new()
	mesh.add_surface_from_arrays(Mesh.PRIMITIVE_POINTS,mesh_data)

I'm doing something wrong here but, I don't know what it is.

Anyway, I just got some information that could be helpful and you might find it interesting. The person who made that devlog video at the beginning of the this thread, replied to my Youtube comment and explained how they moved the vertices around in the video; it's closer to what I suspected. they said:
"It's partly shown in the video. Decal is spawned at collision point, then it's corner points are tested if they are colliding with a map mesh. If some corner point is not colliding - then it's moved closer to the center and so on. these points are shown as small red cubes if not colliding. such method would only work on planes but I tested in goldsrc games decals had similar problem"

xyz

Audiobellum then it's corner points are tested if they are colliding with a map mesh. If some corner point is not colliding - then it's moved closer to the center and so on

That's a very inaccurate and inefficient way to do it. But if it works fine for your project - use it.

Audiobellum

xyz It's how they use it. I'll test it out if I have to but, it would be cool to hear about a better way. Anyway. Could you help me with the problems I'm having with my mesh array? I don't see any meshes being generated in my view port. Is there something wrong with the code?

xyz

Audiobellum Primitive type should be triangles not points. Points are not visible. Also resize the array to ArrayMesh.ARRAY_MAX. You're now resizing to ArrayMesh.ARRAY_VERTEX which is probably zero and your code is likely reporting an error. Always check for error messages as they can be really helpful in figuring out what's wrong.

Btw why don't you just copy-paste the boilerplate part of the code from that page in the docs?

Audiobellum

xyz Thanks for the corrections; it helped and now I can see the triangle. The reason why I don't just copy-paste the boilerplate parts, is because I fear I don't fully understand than the code or that I'm not really learning anything by copying then pasting. I want the information to stick and this process helps.
When I have time, I'm going to try to see if I can get the points around the mesh to behave like they do in the video. That said, could you share with me a more efficient and accurate way of getting the same results?

xyz

Audiobellum could you share with me a more efficient and accurate way of getting the same results?

It's explained in the blogpost I linked earlier. It's mathematically involved though. So if you still struggle with the basics, better not go there for now.