Friction - various surfaces

Questions
#1

I would like to make a game using physics. Collisions between objects are clear to me.
However, I don’t know how I could simulate different ground material.

Suppose I push an object and it moves from the bottom to the top of the screen.
For the object, I can set parameters like mass, friction, etc.

But how to set the material and friction for the surface (i.e. the background) on which the object is moving ? For example, an object will move differently on ice, differently on grass and differently on concrete.

#2

this is an example from the love2d repo:

local player = {
    x = 400,
    y = 400,
    dx = 0,
    dy = 0,
}

local friction = 0.02
local speed = 40

function love.update(dt)
    player.x = player.x + player.dx * speed * dt
    player.y = player.y + player.dy * speed * dt

    player.dx = player.dx * (1 - friction)
    player.dy = player.dy * (1 - friction)

    local kx, ky = 0, 0
    if love.keyboard.isDown('a') then kx = kx - 1 end
    if love.keyboard.isDown('d') then kx = kx + 1 end
    if love.keyboard.isDown('w') then ky = ky - 1 end
    if love.keyboard.isDown('s') then ky = ky + 1 end

    player.dx = player.dx + kx
    player.dy = player.dy + ky

    player.x = math.max(math.min(player.x, 1000), 0)
    player.y = math.max(math.min(player.y, 1000), 0)

end

function love.draw()
    love.graphics.rectangle('fill', player.x - 1, player.y - 1, 3, 3)
end

any questions, just ask!

1 Like
#3

But this is not an example for dynamic physics.

1 Like
#4

You should use the apply_force message and push in opposite direction of travel. You can use the linear_velocity property, normalize it and reverse it to get the opposite direction.

#5

Yes, this is clear to me. If we have 2 elements as in the picture and treat the bottom element as our “floor” on which the other element moves, then the “type of floor” depends on what parameters we set for that object.

image

In my case, we have a top view, meaning the background is my floor.
How to set these parameters for the “background” ?

Another thing. If we let the puck go on the ice at a slight angle and give it some angular velocity, the puck will move in an arc (just like in curling). How to get such a trajectory of the object moving ?

image

#6

If you have different kinds of backgrounds in the same level then use trigger collision objects to detect which background you’re on and apply the appropriate friction.

I have no idea how to simulate this. I think it is beyond the scope of what a physics engine will allow you to accomplish.

1 Like
#7

Too bad. Well, I’ll have to think of something, I won’t give up :slight_smile:

#8

@britzl One more question. Can I dynamically change the value of the friction parameter ? I looked in the documentation and did not find such a possibility

#9

Hi!

Currently no, it’s not possible.

1 Like
#10

@Mathias_Westerdahl And it is in your plans ?

#11

Accessing the properties of the physics shapes is something we’d want yes, but it’s not in our immediate plans unfortunately.

#12

2 posts were split to a new topic: Any virtual keyboard implementations available?

#13

While it might be difficult to realistically and accurately simulate this for all kinds of different objects, it would be quite easy to emulate it by applying a sideways force to the puck based on its angular velocity. Take the linear velocity of the puck, normalize it and get its perpendicular vector, multiply that by the angular velocity and a scale factor, and apply that force to the puck.

If you want to do more, you could try doing some internet research on how the physics of curling works.

2 Likes
#14

You could build this pretty easily without using the inbuilt physics engine, if you know a little lua.

1 Like