2D: Buoyancy Effector with Custom gravity vector

The effector specifying gravity makes things much more complex. Firstly it adds a couple of properties (an option to disable world gravity and one to specify the custom gravity). Secondly, the buoyancy force has to act opposite to the gravity force which means the surface has to be a line perpendicular to that vector. Right now, the surface is a plane that extends, in world-space, along the x-axis to infinity. This makes it fast (for clipping) and simple and covers the common usage case.

Maybe if you can elaborate on the many other applications you're referring to, there might be ways to do it now or that could be considered for the future. All feedback is most welcome.

EDIT: I'm guessing but if you're looking for something that pushes an object out of a collider in a controlled direction then the PointEffector2D can do that.

 

There's a bunch of improvements planned for the buoyancy stuff so watch this space!

 

Indeed I would like to get this as an option but it does add a certain complexity to the calculations. The surface would need some strict constraints:

• Surface is still defined by the surface level
• Surface points in X are X-axis offsets along the surface level
• Surface points in Y are Y-axis offset above/below the surface level
• Outside the supplied points in X, the surface level is used (assumes a Y offset of zero)

Code (CSharp):

1. Vector2[] points = { ... };
2. surfaceEffector.surface = points;

This would allow you to specify an array of points where each point defines an offset along and up/down the surface (see the attached image).

The red arrows define a point offsetting from the surface level to define the surface indicated in yellow. The surface clipping would then be done against the yellow line. Anything outside of the points would just be against the surface level.

You'd be free to change this each fixed-update with no performance overhead as we'd not need to perform any complex checking of the points provided as they're just offsets from the surface.

This obviously isn't guarantee of how it'd work, really just to open a discussion around it.

 

Yes, anything outside of the points you define (along the X-axis). It could even be an option to only use the X-axis range you specify and ignore any buoyancy beyond that.

I'm also wondering if it would be better to be able to specify the number of points in the X-axis in the effector? We could set the point count, spacing and x-axis offset. This would give you a span of equally spaced points and you would only have to supply an array of Y offsets (array of floats) which provides some added benefits:

• Much quicker, less data, no need for sorting the X-axis offsets.
  
• You would be allowed to read/write individual points rather than having to read/write the whole array.
• You could have a gizmo that allowed you to drag the points up/down in the scene.
• You could have more points than you show on screen and simply adjust the 'surfaceOffset' to make the surface move left/right (thinking waves moving left/right without having to modify the surface).
• Possible to allow 'wrapping' of the points provided out to infinity (thinking of a wave surface that repeats infinitely)

Code (CSharp):

1. // Surface is 100 points, no offset but equally spaced by 0.25 each.
2. buoyancy.surfaceCount = 100;
3. buoyancy.surfaceOffset = 0.0f;
4. buoyancy.surfaceSpacing = 0.25f;
5.  
6. // Access whole surface offset array.
7. float[100] surfaceOffsets = { ... };
8. buoyancy.surface = surfaceOffsets ;
9.  
10. // Access individual surface offsets.
11. for (var i = 0; i < 100; ++i)
12.    buoyancy.setSurfaceOffset (i, surfaceOffset[i]);
13.  
14. // Set the whole surface level up/down.
15. buoyancy.surfaceLevel = 5.0f;

Nothing is written in stone, feedback welcome.