Can you use vertex paint instead of weight paint?
An alternative to weight paint is Vertex Paint. Vertex paint can be, unlike weight paint, accessed in cycles. After applying your modifier, you can use the information in this answer to convert your weight paint data to Vertex Colors.
How can I set and get the vertex color?
Blender doesn’t have a (non-Python) way to set the Vertex Colors per selected vertex/vertices. Per face is however, as stated below, not a problem. There is no built-in interface (yet) to get the rgb value of a selected Vertex. Each vertex can be shared by a number of faces, therefore a vertex doesn’t necessarily have one color associated with it.
How do you paint vertex groups in Blender?
As you can see, I use a VertexWeightProximity modifier, to paint the vertex group, and I would like to use it in the node tree to affect the transparency of the mesh. The attribute node doesn’t seem to read vertex groups yet. This method doesn’t use weights, but it seems that your real goal is to get the proximity into Cycles.
How are colors stored in a vertex layer?
Behind the scenes the Vertex Colors are not stored in the data per vertex but in a Vertex Color layer, which stores vertex colors for each face of the mesh. Possibly this explains that a bit more clear. There are 9 verts in this subdivided plane, and the middle vertex is used in 4 faces and therefore has 4 different colors associated.
Is there an alternative to weight paint in cycles?
An alternative to weight paint is Vertex Paint. Vertex paint can be, unlike weight paint, accessed in cycles. After applying your modifier, you can use the information in this answer to convert your weight paint data to Vertex Colors. Once this is complete, simply use an attribute node:
How can I see the weights of the vertex group?
When you are in Edit Mode, you can make the weights of the active group visible on the mesh: Select the Viewport Overlays popover from the header of the 3D Viewport. And there enable the Vertex Group Weights option. Now you can see the weights of the active vertex group displayed on the mesh surface.
How do you find the weight of a vertex in Blender?
As mentioned before in Vertex Groups each entry in a Vertex Group also contains a weight value in the range of (0.0 to 1.0). Blender provides a Vertex Weights panel from where you can get (and edit) information about the weight values of each Vertex of a mesh. That is: to which Vertex Groups the vertex is assigned with which weight value.
How to map vertex weight to vertex groups?
You need to translate vertex weight into some proxy that nodes can read. Consider using UV as a proxy. It can be read by nodes and it can easily be mapped to vertex group weight. Create a new UV mapping for your mesh and set all vertices to 0,0 on that new map.