[Beta 2] RigiBody velocity

MagicLord

Hi there,

Rigibody physics collision randomly go through floor and re position itself, it happens because i apply a negative velocity to simulate gravity. Is Kinematic a better way ?

You can download the project and use right or left keys to move the physics [ https://upload.cat/f89fe85f1b125b35]( https://upload.cat/f89fe85f1b125b35 " https://upload.cat/f89fe85f1b125b35")

MagicLord

Decreasing gravity velocity based on distance to floor will avoid this problem.

wombatstampede

RigidBodies shouldn't be forced with set velocities or set positions if ever possible. (At least not all the time)

Instead use apply_impulse to apply forces like gravity (i.e. in fixed_process)

Example:

var gravity=Vector3(0,get_mass() * -9.8,0)*delta
apply_impulse(Vector3(),gravity)

This example is for 2.1. I hope it works the same way on godot 3. The first parameter to apply_impulse is the location offset (in global world space) where to apply the force (gravity). So if you have another center of gravity than 0,0,0, you could place a child spatial in your rigid body and use the global position difference of body and child spatial to get the needed offset.

The second parameter is the force/impulse vector to apply to the body. This vector is also in global coordinate space. In my example I created a simple y-downward vector with 9.8m/sec².

MagicLord

@wombatstampede said: RigidBodies shouldn't be forced with set velocities or set positions if ever possible. (At least not all the time)

Sure, i find characters sometimes can be stuck inside a physic platform shape because i use velocity. Apply_impulse should give better predictable results. Thx.

MagicLord

@wombatstampede said: RigidBodies shouldn't be forced with set velocities or set positions if ever possible. (At least not all the time)

Instead use apply_impulse to apply forces like gravity (i.e. in fixed_process)

Example:
var gravity=Vector3(0,get_mass() * -9.8,0)*delta
apply_impulse(Vector3(),gravity)
This example is for 2.1. I hope it works the same way on godot 3. The first parameter to apply_impulse is the location offset (in global world space) where to apply the force (gravity). So if you have another center of gravity than 0,0,0, you could place a child spatial in your rigid body and use the global position difference of body and child spatial to get the needed offset.

The second parameter is the force/impulse vector to apply to the body. This vector is also in global coordinate space. In my example I created a simple y-downward vector with 9.8m/sec².

I'm using apply_impulse on character capsule with continuous cd, it can sometimes go through floor when impulse has values greater than 30 , Godot 3 physics are not reliable.

wombatstampede

Yes the physics engine is far from being unbreakable. That was the case in 2.x and seems still to be the case in Godot 3. There are multiple possible reasons.

One possible reason is the sample rate (Engine.iterations_per_second on godot 3). If an object moves very fast then it could be at one time before the collision object and 1/60th second later it already has passed the object (or more than half of the collision shape(s)). So you could try to increase the iterations_per_second. But naturally, this also has an impact on the performance.

You also can try to make the collision shape "thicker".

Finally, you could do Raycasts to detect collsion shapes in the way. This might be helpful when using fast moving objects like bullets/rpgs where you only need the collision-info but not necessarily a physically correct reflection.

Edit: I now had a short look at your script (the initial version). I'm unsure if a RigidBody is really ideal for your needs (2.5D Platformer). The few 3.0 3d demos have a demo for a kinematic_character. Maybe this can be of help/inspiration?

MagicLord

@wombatstampede said: Yes the physics engine is far from being unbreakable. That was the case in 2.x and seems still to be the case in Godot 3. There are multiple possible reasons.

One possible reason is the sample rate (Engine.iterations_per_second on godot 3). If an object moves very fast then it could be at one time before the collision object and 1/60th second later it already has passed the object (or more than half of the collision shape(s)). So you could try to increase the iterations_per_second. But naturally, this also has an impact on the performance.

You also can try to make the collision shape "thicker".

Finally, you could do Raycasts to detect collsion shapes in the way. This might be helpful when using fast moving objects like bullets/rpgs where you only need the collision-info but not necessarily a physically correct reflection.

Edit: I now had a short look at your script (the initial version). I'm unsure if a RigidBody is really ideal for your needs (2.5D Platformer). The few 3.0 3d demos have a demo for a kinematic_character. Maybe this can be of help/inspiration?

I used kinematic it but it made my code too complex to manage curve jumping while a physic engine can handle movement and gravity for you. My character has a raycast to detect floor and manage jumping, perhaps i'll use it to detect distance to ground and decrease the gravity impulse force, this should avoid the character going through cube meshes platforms. Thank you or your help.