Delta Time not used in Rigid Body Physics and strange behavior #110160

New Issue

Shmuel Israel · 2023-07-16T06:45:24+02:00

Shmuel Israel commented

2023-07-16 06:45:24 +02:00

System Information
Operating system: Windows-10-10.0.19045-SP0 64 Bits
Graphics card: NVIDIA GeForce RTX 2070 with Max-Q Design/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 535.98

Blender Version
Broken: version: 4.0.0 Alpha, branch: main, commit date: 2023-07-02 22:31, hash: 7be0d1481c67
Worked: ?

Explanation
I was working in GN on some particle physics and wanted to see what gravity was actually supposed to look like, so I added a rigid body physics to another object. I saw that something wasn't adding up, so I tested further. I changed the frame rate and observed that the rigid body was getting faster and slower, depending on the frame rate, as well as exhibiting strange behavior (speeding up then slowing down).

Short description of error
rigid body physics exhibiting different behaviors depending on frame rate, as well as speeding up and slowing down (this might be a bake issue or the delta time only taking effect later 🤷‍♂️)

Exact steps for others to reproduce the error

set up a rigid body physics
see the speed of the gravity
change the frame rate
see that there is now a different gravity speed
(there may also me some strange behavior, that the speed gets faster then slower, this could also happen when switching frame rates back to what was normal before)

**System Information** Operating system: Windows-10-10.0.19045-SP0 64 Bits Graphics card: NVIDIA GeForce RTX 2070 with Max-Q Design/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 535.98 **Blender Version** Broken: version: 4.0.0 Alpha, branch: main, commit date: 2023-07-02 22:31, hash: `7be0d1481c67` Worked: ? **Explanation** I was working in GN on some particle physics and wanted to see what gravity was actually supposed to look like, so I added a rigid body physics to another object. I saw that something wasn't adding up, so I tested further. I changed the frame rate and observed that the rigid body was getting faster and slower, depending on the frame rate, as well as exhibiting strange behavior (speeding up then slowing down). **Short description of error** rigid body physics exhibiting different behaviors depending on frame rate, as well as speeding up and slowing down (this might be a bake issue or the delta time only taking effect later 🤷‍♂️) **Exact steps for others to reproduce the error** - set up a rigid body physics - see the speed of the gravity - change the frame rate - see that there is now a different gravity speed - (there may also me some strange behavior, that the speed gets faster then slower, this could also happen when switching frame rates back to what was normal before) <video src="/attachments/a3513a54-1f94-41e9-a043-9a0cea3652e1" title="2023-07-16 00-22-27.mp4" controls></video>

2023-07-16 00-22-27.mp4

2.9 MiB

Shmuel Israel added the

labels 2023-07-16 06:45:24 +02:00

YimingWu commented

2023-07-16 10:18:35 +02:00

Hi @shmuel , the physics is reset if you go back to frame 0, then after changing the fps it should re-calculate everything based on the new setup.

Should probably reset the physics cache when frame rate is changed. Having a similar reset call like in #108004 could be a good way to go about it.

Hi @shmuel , the physics is reset if you go back to frame 0, then after changing the fps it should re-calculate everything based on the new setup. Should probably reset the physics cache when frame rate is changed. Having a similar reset call like in #108004 could be a good way to go about it.

YimingWu added

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Delta Time not used in Rigid Body Physics and strange behavior #110160