koobas.hobune.stream
How can I slide a cube perfectly over a changing surface?
I've had a hunt around but can't find anything to answer exactly this.
Here, the rigidbody cube is trying to slide around inside a capsule mesh collider, but it's toppling over when it has hit one of the edges between polys:
I want it to simply keep sliding around perfectly, so when the leading base edge of the cube hits a new incline, it just keeps sliding on up it.
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The surface is a custom mesh, so could be anything.
I want this behaviour so that Unity's physics can sort out the cube's orientation, then I take the normal of the cube's base (and not the normal of the surfaces it is resting on).
Is there a non-fudge-it way to do this?
So hang on - how would you define it's base? Presumably the base would rest based on it's support at a number of points - you're going to have to work that out I imagine. Where it's resting...
Oh, I forgot to mention it will be using rigidbodies.
It is resting on the surface as a cube normally would. But unlike reality, I don't want it to topple forward if it hits an incline. Rather, it just keeps sliding smoothly.
A bit hard to describe simple things without images. :/
The mesh is literally just a capsule with the normals turned inside out so I can move around its inside. I made the capsule in Blender; a UV sphere with its middle edge loopjust extruded out into a longer capsule shape.
Is it normal that lots of our posts get cut?
Racing game, ok.
I built this object in, of all things, LittleBigPlanet and, amazingly enough, it seems like the same strategy would work here. (O_O)
Each Update (or whatever):
Move Cube along its forward.
For each 'corner' which must remain grounded:
If (or, dangerously, while) a raycast from (that Corner plus Cube-Up)
to Cube-Down does not hit the current surface
OR
A raycast from Corner to Cube-Down hits the current surface, but only
after an unacceptable distance:
Choose a Pivot point (should be defined per Corner;
using the center of Cube ends up showing some clipping)
Rotate Cube around Pivot towards this Corner
If (while) the raycast from (Corner plus Up)
to (Corner) hits the surface:
Choose a pivot point and rotate *away* from this Corner
This might be very similar to Fattie's answer; you could use repulsion/attraction forces at the Corners instead of pivot points.
So basically if a corner is airborn, rotate the cube so that it's not.
Not sure how to choose those pivot points; could be 3 corners off the ground. Also, what do you mean by "Cube-Up"? The cube's local height? Likewise with Cube-Down, and in line 12, "Up".
Yep.
Those are local directions. World-Up is Vector3.up, Cube-Up (Up) is cubeTransform.up
I imagine that pivot point would simply be the edge that remains on the ground, or in some cases, the single corner that remains on the ground.
I haven't tried this approach yet though. Just writing that for any readers.
May this could work: you do not move the cube directly but handle a projector of some kind. Think of the bowl if it was a completely hollow sphere. Place a Gameobject in it's center of which you controller the rotation. Shoot 4 raycasts onto the innersurface of the bowl where they have the approximate distance of the cubes bottom corners from each other. Maybe by checking a 5th center raycast. Then get a plane through all the contactpoints and rotate and transform your cube about it. This would make the cube move nearly precise I guess.
Even if that's not what you had in mind it might help thinking about the problem another way.
note that fortunately if it's an actual sphere, the solution is trivial - the cube just points towards the centre all the time. you can do it instantly in unity with "TrickHolder" as described above, fortunately
