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(DP) Paint not following object, when object constraint to dp weight created vertex group
Open, Needs Triage by DeveloperPublic


System Information
Operating system: Windows-10-10.0.18362 64 Bits
Graphics card: GeForce GTX 970/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 388.13

Blender Version
Broken: version: 2.81 (sub 16), branch: master, commit date: 2019-10-27 13:40, hash: rB9b6aa740be31
also broken in 2.80 release
Worked: (optional)

Short description of error
I want to control the location of an object by drawing weight paint on a plane and constraint the object to this vertex group created by the weight paint. The problem occurs when the object with the constraint should also be a brush painting colors on the plane. The colour will not follow the object, but stay at the objects "original origin".


Exact steps for others to reproduce the error

add collection called paint
add collection called weight

plane (master or other collection):

add a plane, scale largers, subdive a lot (e.g. 50 time)
add 2 dynamic paint canvas:
    1. name weight, surface type weight, Brush Collection = weight; check Dissolve, output/add dp_weight vertex group 
    2. name paint, surface type = paint, Brush Collection = paint, (check Dissolve), output/add dp_wetmap vertex group 
add a material with attribute node with dp_wetmap, fac connected to emission --> material output (node wrangler/strg+shift+click on attribute node)

Add a cylinder (will mark the spot for the cube to be via dp weight on the plane)

 add a cylinder 
scale a bit bigger and set to viewport display = wireframe 
 move it that it touches the plane 
 add dp brush 
 move it to the "weight" - collection


add a cube
add dp brush
constraints: add copy location 
    target= plane 
    vertex group = dp_weight

--> when you press play and move the cylinder (eevee or cycles), the cube will follow the cylinder, but the paint will stay at the "original origin" of the cube

If you would constrain the cube to the location of the cylinder, the cube will brush paint as expected.

I hope you can reproduce and find the problem. ... At one point of setting up this exact example for you I added keyframes to the cube and it painted correctly .... I tested that because of another bug in the same setup, where the cube is not following the cylinder when it has location keyframes (minimum of two) if the keyframes overwrite the constraint. However, in the minimal setup I can't reproduce it. So if you have an idea connected to it to it go for it... I'll try to find a setup that makes clear where the problem comes from

thanks for your work.



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