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Rotate a stick around a ball ? — Gideros Forum
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    Rotate a stick around a ball ?

    lightlight Member
    edited June 2015 in Game & application design
    In my billiard game , m showing projection of cue ball on mouse events . Simultaneously i also want to move the billiard stick around the cue ball in the direction of projection on mouse event . How can i do that ?
    I have done by calculating slope and some more lengthy stuff .
    Just wanted to know, is there an easier way to achieve this.
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    Comments

    • ar2rsawseenar2rsawseen Maintainer
      edited June 2015 Accepted Answer
      You basically need to calculate two things
      1) x,y position of constant distance away from the ball at provided angle
      2) angle in which to rotate the stick so it will always be directed to ball

      So lets say your ball is at x1,y1 and mouse is at x2, y2 coordinate.

      Calculate a vector
      dx = x1-x2
      dy = y1-y2

      From top of my head:

      1) Find a pointX, pointY which, let's say is 100 pixels far from ball on dx,dy vector
      local fromDistance = 100
local ratio = math.sqrt((fromDistance*fromDistance)/(dx*dx + dy*dy))
local pointX = x1 + dx*ratio
local pointY = y1 + dy*ratio
      So you need to position stick at pointX,pointY

      2) Find angle of vector
      local length = math.sqrt(dx*dx + dy*dy)
local angle = math.acos(dy/length)
 
--this part depends on how your original image is rotated		
if(dx > 0) then
    angle = -angle
end
      If stick by default was rotated to 0 degree, then simply apply angle to stick, note that angle is in radians, you need to convert it to degrees to use on sprite with math.deg(angle)

      have not tried the code, so may contain errors, but logic should be somewhat correct :)

      More info on similar problems:
      http://giderosmobile.com/forum/discussion/2828/new-day-new-problems-rotate-an-physics-object-towards-direction-of-movement/p1
      http://appcodingeasy.com/Gideros-Mobile
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    • lightlight Member
      edited June 2015
      @ar2rsawseen
      Thanks , i have done something like that and it works . But got stuck to new problem , to hit the cueball with stick i have to pull back stick in that particular line of direction .Dont know how to pull back stick ?

      I have seen this kind of behaviour in prismatic joint , but dont know how to apply it here.
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    • ar2rsawseenar2rsawseen Maintainer
      Well you can calculate distance on vector changing 100 to larger value to change cure position further from center, and on release apply impulse into the way of the ball
      http://appcodingeasy.com/Gideros-Mobile
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    • lightlight Member
      edited June 2015
      @ar2rsawseen
      Oh yes it was right there . i mean logic
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