--move objects
function _update()
move(pl)

end

--move and collission functions

function move(obj) 

 if (btn(0)) then 
 obj.dx-=obj.acc --move left amount
 end

 if (btn(1)) then 
 obj.dx+=obj.acc --move right amount
 end

 if (btnp(5)) then 
 obj.dy-=obj.boost --move up amount when jump
 end

 --reduce vertical movement by gravity each update
 obj.dy+=gravity
 --reduce horizontal movement by friction
 obj.dx*=friction

 --limit max speed in all directions
 obj.dy=mid(
 -obj.max_dy,
 obj.dy,
 obj.max_dy)

 obj.dx=mid(
 -obj.max_dx,
 obj.dx,
 obj.max_dx)

    --new locations if movement applied
 obj.newx=obj.x+obj.dx
 obj.newy=obj.y+obj.dy

 --check whether new locations collide with other objects
 --will adjust newx/newy positions to not overlap collided object

        for v in all(things) do
        if v!=pl then
        --check collision of new vertical
    box_hit(obj,v,"y")
    --check collision of new horizontal
    box_hit(obj,v,"x")
            --apply new positions (adjusted to stop before collide)
    end
    end

 obj.y=obj.newy 
 obj.x=obj.newx     

 obj.y=mid(0,obj.y,120)
 obj.x=mid(0,obj.x,120)

end

function box_hit(obj,obj2,axis)

--compares one object x/y/w/h to another  
--axis is which dimension of movement being checked
--hitbox different depending on direction

  if axis=="y" then
  y1=obj.newy
  x1=obj.x

  elseif axis=="x" then
  y1=obj.y  
  x1=obj.newx
  end

  w1=obj.w
  h1=obj.h
  x2=obj2.x
  y2=obj2.y
  w2=obj2.w
  h2=obj2.h

  --collision check method 
  --if distance between midpoints greater than 
  --the sum of the two box halves

  --distance mid points
  local xd=abs((x1+(w1/2))
  -(x2+(w2/2)))
  --sum of box widths/2
  local xs=w1*0.5+w2*0.5
  --distance mid points
  local yd=abs((y1+(h1/2))
  -(y2+(h2/2)))
  --distance mid points
  local ys=h1/2+h2/2

if xd<xs and 
   yd<ys then 

--is a collission    

  if axis=="y" then
    --kill vertical momentum
                obj.dy=0
    if y1<y2 then
    --if collide from above limit movement to last non collide point 
    obj.newy=flr(y1-(ys-yd)) 
    else 
    --if collide from below limit to lowest point of 2nd object
    obj.newy=ceil(y2+h2) end

  else
    --kill horizontal momentum
                obj.dx=0

    if x1<x2 then
    --if colliding from left
    obj.newx=flr(x2-obj.w) 
    else 
    --if colliding from right
    obj.newx=ceil(x2+w2) end

 end
 end