fossil swallow
Does anyone know why a call to PhysicsServer3D.body_test_motion with a high margin (0.15) doesn't register a collision but the same call with a low margin (0.0001) does? I would expect it to be the opposite
In the attached picture I have a cylinder walking forward into a wall. direction_test_collides is returning as false but the same test with a smaller margin is returning true (direction_test_collides_no_margin)
cosmic dock
margin is used to solve overlaps at the start and end of the motion
so the order of operations is:
margin)margin)0.15 is a giant margin to be using in 3D physics
it's supposed to be numerically insignificant
fossil swallow
So with a large margin like that right up on another shape is step 1 pushing the body back farther than my test motion?
Its not clear why step 1 is happening at all. The way the documentation is phrased I'd expect flatly more collisions with a larger margin
cosmic dock
oh, are you trying to use it like a shape cast?
it's not that
body_test_motion is meant to be used by character controllers
it only registers one collision at a time
fossil swallow
Right, I'm working on adding stair stepping to a characterbody3d
fossil swallow
oh, are you trying to use it like a shape cast?
What do you mean by this?
cosmic dock
So with a large margin like that right up on another shape is step 1 pushing the...
I believe this is what's happening
had to reference the source code again to be sure
cosmic dock
What do you mean by this?
since you mentioned "more collisions" I assumed you wanted more than one collision result at a time
fossil swallow
I just meant I'd expect it to be catching more of the level
cosmic dock
here is the 2D version of body_test_motion for reference (it's bad)
https://github.com/godotengine/godot/blob/4e990cd7e51d17cf24f854cc33b2715eaa27200f/servers/physics_2d/godot_space_2d.cpp#L535
fossil swallow
in the sample code I repeated the same test with a larger and a smaller margin. for any given test I'd expect a larger margin to catch more of the level
cosmic dock
I just meant I'd expect it to be catching more of the level
the margin is only used for collision resolution, not the motion cast
to cast a body with a certain margin, you'll want to use the shape cast node
which does account for the margin you provide it
I believe it uses a method like cast_motion under the hood?
update: yep it's cast_motion
fossil swallow
I can't use a shapecast node since the directions I need to test aren't known at design time
cosmic dock
you can change the direction and transform of the shapecast node and force it to update at any time
you can use physics server directly or the node - both work
fossil swallow
That seems needlessly cumbersome
Is it best practice then to just have a shapecast node hanging off my character to do these kinds of tests
I'm assuming this is the method you're talking about?
https://docs.godotengine.org/en/latest/classes/class_shapecast3d.html#class-shapecast3d-method-force-shapecast-update
Are there any considerations to using the same shapecast multiple times in a single frame or do I need to have as many shapecast nodes as tests I want to run?
cosmic dock
this is the method ShapeCast3D uses under the hood
using the node just lets you configure the parameters more easily in the editor
fossil swallow
Thanks for the information by the way, any frustration I'm expressing is with the engine and not with you or your help
cosmic dock
i understand 
fossil swallow
I have a quick follow up if you don't mind since you seem very knowledgeable about the physics engine. I've run into issues trying to use the CharacterBody3D methods move_and_slide and move_and_collide in the same frame. It looks like move_and_slide resets the position of the character and move_and_collide doesn't set any of the nice is_on_floor flags
Is there any way to trigger those checks without calling move_and_slide or if not are there any considerations to manually manipulating the velocity and calling move_and_slide multiple times in a frame?
cosmic dock
You might be at a point where you should stop inheriting from CharacterBody3D
move_and_slide uses move_and_collide once every iteration and is the only function that can update the state of the character body
there's a lot of code, but it is definitely possible to rewrite this in GDScript or C#
cosmic dock
I have a quick follow up if you don't mind since you seem very knowledgeable abo...
you can probably set the max_slides property to 1, temporarily change velocity, and call move_and_slide to achieve what you want
but once you hit a certain level of complexity it makes more sense to inherit from AnimatableBody3D than CharacterBody3D
or any physicsbody for that matter
they all have access to move_and_collide (for some reason??)
btw move_and_collide is essentially just body_test_motion but more convenient
so I'd use that unless you need to set the starting point of the motion
fossil swallow
I would but I don't want to actually move the character unless there's a path. Otherwise I can climb walls haha
cosmic dock
move and collide has a test_only argument
the only difference is that you can't give it a from transform as an argument
fossil swallow
True but I have to make 3 tests before actually moving. Up over down