How to get vert normal before transform from skinning/animation/posing, or how to reproduce same transforms in shader?

pineapple · May 12, 2024, 10:42pm

Godot Version

v4.2.1.stable.mono.official [b09f793f5]

Question

The value of NORMAL in the vertex function of a spatial shader has already been transformed according to rotations applied by the pose of a skeleton. In my material, I need the original, unmodified vertex normal, within the vertex shader. How can I get this value?

roc4u1000 · May 12, 2024, 11:33pm

This should cache the pre-transformed vertex normals, and here I am just drawing them on the ALBEDO.

varying vec3 vert_normals;

void vertex() 
{
	vert_normals = NORMAL;
}

void fragment() 
{
	ALBEDO = vert_normals;
}

pineapple · May 13, 2024, 10:14am

No, this doesn’t work for me. The NORMAL value has already been transformed upon assignment to vert_normals in that example. I am not talking about model*view transformation. I am talking about transformation from skeletal animation. When the vertex is influenced by one or more bones, and those bones have been moved from the rest position, it is not clear how to obtain the original vertex normal already within the vertex function, because NORMAL was already transformed according to the pose.

Anyway, I should note that for my use case, it would also/alternatively be helpful if I could have access to whatever matrix or other data was used to transform NORMAL from whatever was baked into the vertex attribute to whatever is finally received in the vertex shader. Really, what I need to do for the material I’m currently working on, is apply the same transformation to custom vertex data.

I think I could achieve what I’m trying to, if I knew how to access bone_transforms here in the vertex shader. (The docs already mention BONE_INDICES and BONE_WEIGHTS, just no way I see to get the transforms.)

github.com

godotengine/godot/blob/d48be8c5ef3d3d1eccf63a198338ded14e301e23/servers/rendering/renderer_rd/shaders/skeleton.glsl#L37


      
          src_bone_weights;
          
          layout(set = 1, binding = 2, std430) buffer restrict readonly BlendShapeData {
          	uint data[];
          }
          src_blend_shapes;
          
          layout(set = 2, binding = 0, std430) buffer restrict readonly SkeletonData {
          	vec4 data[];
          }
          bone_transforms;
          
          layout(push_constant, std430) uniform Params {
          	bool has_normal;
          	bool has_tangent;
          	bool has_skeleton;
          	bool has_blend_shape;
          
          	uint vertex_count;
          	uint vertex_stride;
          	uint skin_stride;

roc4u1000 · May 13, 2024, 7:58pm

Can you show what you are seeing, and an example of what you are after? Like if you have a rigged character standing there, and you grab the arm and rotate it down or play and animation, what are the normal vertex values expected to do, like if you drew them in the albedo.

pineapple · May 13, 2024, 8:49pm

After a lot more investigation, I realized that what I wanted to do is apparently just not possible right now.

Technically, I was in fact able to get the normals before bone transforms by baking it into extra UV layers. This lets me check UV2 and CUSTOM0 in the vertex shader to get the original, unmodified vertex normal, before transforms from posing. So at least that strictly solves the original question I asked. But this didn’t solve the actual problem that I was having, like I expected it to.

I made a feature proposal to expose a BONE_TRANSFORM in vertex shaders.

github.com/godotengine/godot-proposals

Add BONE_TRANSFORM built-in to vertex shader

opened 11:09AM - 13 May 24 UTC

pineapplemachine

topic:shaders topic:3d

### Describe the project you are working on I am working on a 3D game using an …inverted hull shader to help character models stand out from their backgrounds. In my case, I cannot just extrude the outline hull along normal vectors, because my models do not all have smoothed normals. I have written a Blender script that computes and bakes outline extrude vectors into extra UV layers, and I have written a shader in Godot that reads that data and uses it to create the outline hull. ### Describe the problem or limitation you are having in your project Generally, this approach is working well for me. The problem is that when the mesh this outline is applied to is animated using a skeleton, I do not have any way to apply a transform from skinning to the extrusion vectors (i.e. the same transform as Godot has automatically applied to the vertex `NORMAL` upon entering the vertex shader). Though I have access to `BONE_INDICES` and `BONE_WEIGHTS` in the vertex shader, I do not have access to the buffer containing the bone_transforms. Related: https://github.com/godotengine/godot/blob/d48be8c5ef3d3d1eccf63a198338ded14e301e23/servers/rendering/renderer_rd/shaders/skeleton.glsl#L37 ### Describe the feature / enhancement and how it helps to overcome the problem or limitation In my particular case, exposing `bone_transforms` data to the vertex shader - or, more conveniently and probably more realistically, a single `BONE_TRANSFORM` mat4 - will allow applying the appropriate transforms to the outline extrusion vectors in my outline shader. This would presumably be useful for many other materials as well. ### Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams For example: ``` void vertex() { vec3 extrusion_vec = normalize((vec4(baked_extrusion_vec, 0.0) * BONE_TRANSFORM).xyz); } ``` ### If this enhancement will not be used often, can it be worked around with a few lines of script? I may be able to get a reasonable result by representing my baked extrusion vectors as transforms upon the normal? That's what I'm going to try next. But this is janky and inconvenient, is likely to be affected by floating point error, and at least on my end my problem could be easily solved by having access to this transform that Godot already computes per-vertex, in order to transform vertex positions, normals, and tangents, and currently is just not exposing. ### Is there a reason why this should be core and not an add-on in the asset library? As far as I know, this is not possible to achieve with an addon.

In the meantime I figured out a janky workaround involving creating a second mesh and cramming the data I need transformed with bones into that mesh’s normals.

system · June 12, 2024, 8:50pm

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