Acceleration with dt

[icekiller8002]

Hi there, I am trying to make a jumping movement with delta time (compatible with any framerate). Unfortunately, I am struggling to accomplish this. The original code that is not compatible with dt is below:

Code: Select all

-- jumping
if player.jumping then
  -- prevents legs from moving whilst jumping
  if player.frame ~= 0 or player.aTimer ~= 0 then
    player.frame = 0
    player.aTimer = 0
    legsQuad:setViewport(60*player.frame,player.legY,60,15,legs:getDimensions())
  end

  if not player.falling then
    if player.acceleration >= 15 then
      player.falling = true
    else
      player.y = player.y - (15 - player.acceleration)
      player.acceleration = player.acceleration + 1
    end

    if not player.soundPlayed then
      playSound("jump")
      player.soundPlayed = true
    end
  end
end

Any help or direction to making this code dt-compatible would be appreciated.

[ivan]

There is a difference between velocity and acceleration. Generally speaking the formula is
change in position = velocity*dt
With jumping you want to set the velocity once and let the body fall due to gravity.
https://2dengine.com/?p=platformers

[pgimeno]

The simplest integrator uses these formulas:

velocity = velocity + acceleration * dt
position = position + velocity * dt

[mxmlnbndsmnn]

For a simple acceleration mechanic I used something like this:

Code: Select all

player.body.x = player.body.x + player.body.velocity.x * dt
player.body.y = player.body.y + player.body.velocity.y * dt

... for the actual movement where velocity.x and .y are equal to the current speed in these directions. And

Code: Select all

player.body.velocity.x = acc.x * targetSpeed.x + (1-acc.x) * player.body.velocity.x

with an acc value between 0 and 1 (in fact, less than 0.1). The target speed is something like the current maximum speed that the player wants to reach. This value can be changed, say depending on the ground the player is standing on, or if he is currently in the air. (Do the same for the y acceleration in case you have a top down view on the player)