Fix RigidDynamicBody gaining momentum with bounce #55313
Conversation
Bounce calculation now uses the previous frame's velocity, so it's consistent with the actual motion of the bodies involved and not the yet-to-be-applied forces. When bounce is 1, using the current velocity was causing the new forces (including gravity) to be taken into account, which lead to the bounce velocity to be higher than the falling velocity at the moment of impact, adding more and more energy over time.
|
Thanks! |
|
This is such an important fix for 3.x 2D physics (physics materials) that leaving it out due to compat-breaking worries is not, in my view, reasonable. I battled for several nights recently trying to understand why bounce caused continuous jitter in 3.5.2 2D physics. After seeing the various known recorded bugs around this issue, I finally concluded that it's best to use physics materials with bounce very, very sparingly, e.g. only in a few surfaces, and keeping the bounce value below 0.5 to reduce the infinite jitter dance. I would like to see this important fix backported to 3.x and set as default OFF in settings, so that it will not affect existing games, but can be used by new projects. My blog post about this here: https://godotyourself.blogspot.com/2023/04/hold-my-beer.html Linux and Windows builds of 3.5.2 with the fix here: https://github.com/belzecue/godot-af/releases/tag/3.5.2-stable-af-phys-bounce-fix UPDATE: PR for backporting this change to 3.x: #76216 |
Bounce calculation now uses the previous frame's velocity, so it's consistent with the actual motion of the bodies involved and not the yet-to-be-applied forces.
This is due to the order of update in the solver:
When bounce is 1, using the current velocity was causing the new forces (including gravity) to be taken into account, which lead to the bounce velocity to be higher than the falling velocity at the moment of impact, adding more and more energy over time.
This change can be considered compatibility breaking, because it changes the effect of bounce and might require users to modify their physics material or damping settings to keep the same behavior in some cases.
Fixes #25186 (tested with MRP from #24332)
Fixes #52550
Helps with #29639 but doesn't fix it completely, as contacts are still adding energy.