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Won't Fix
Votes
0
Found in
6000.0.64f1
Issue ID
UUM-128662
Regression
No
[VFX] Incorrect Behavior in VFXUpdate
Steps to reproduce:
- Import attached package in URP project with VFX package available
- Open VFX "UUM_128198_Simplified_Repro"
- Open Scene
Actual results:
The two sphere have different radius:
!image-2025-11-26-17-08-06-191.png|thumbnail!
There are three ways of change if:
- Disable Set Scale block in Update (which is actually writing scale \{1,1,1})
!image-2025-11-26-17-09-22-277.png|thumbnail!
Or
- Switch to Runtime Mode
!image-2025-11-26-17-10-02-537.png|thumbnail!
Or
- Enable Debug Symbol in VFX preference
!image-2025-11-27-13-40-16-151.png|thumbnail!
Expected results:
The two sphere have the same radius:
!image-2025-11-26-17-05-36-301.png|thumbnail!
Reproducible with versions: 6000.64f1
Not reproducible with versions: 6000.1.0a6
Can’t test with versions: N/A
Tested on (OS): Windows
Notes:
- The issue has been involuntary fixed by the change #55907 (152ffc69c650565c8c7c99143ea14c70824ebeb4) which optimize attribute layout and this exact issue isn't reproducible with more recent revision
- This is reproducible in runtime (see Repro_Simplest_UUM_128198, it plugs properties to boolean slot in the update context)
- The failure seems to come from FXC, same shader, look at `store_raw` count in IL output, we except 7 values (32bits) written, so, at least two store_raw (which handle 4 value written)
- [https://shader-playground.timjones.io/7ab31914c581a1155cf38cd25da39c20] in cs_5_0 🔴
- [https://shader-playground.timjones.io/0e336f681f9718c3ad7d1e510384e69e] in cs_5_1 🟢
- The problem is not reproducible on PS4/PS5/XboxOne/XboxSeries (because these platform doesn't use FXC)
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Resolution Note:
Thank you for reporting this bug to Unity.
Unfortunately, as you well described, the root cause of this issue is an implementation flaw in FXC, and it cannot be resolved without migrating to a more modern shader compilation solution.
For now, we will be closing this report. Thank you again for taking the time to submit it. If anything changes regarding the impact or severity of this issue on your project, please let us know.