--function to scale and offset 
--the x co-ordinate when pixel
--size is changed

function scale_x (x)
local newx=x*pixels
local offset=newx-x
local x1=x+newx-pixels*28
local zero=camera_x+64-pixels*(camera_x+64)
x=(zero+newx)
return(x)
end

--function to scale and offset 
--the y co-ordinate when pixel
--size is changed

function scale_y (y)
local newy=y*pixels
local offset=newy-y
local y1=y+newy-pixels*28
local zero=camera_y+64-pixels*(camera_y+64)
y=(zero+newy)
return(y)
end

--moves all objects
--calls boxhit function that
--checks colisions

function move(obj) 

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

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

if btn(2) then 
obj.dy-=obj.acc --move up amount when jump
sound=true
end

if btn(3) then 
obj.dy+=obj.acc --move up amount when jump
sound=true
end
end

--reduce vertical movement by gravity each update
--obj.dy+=obj.gravity

--reduce horizontal movement by friction
obj.dx*=obj.friction
obj.dy*=obj.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 obj!=v then
--check collision of new vertical
-- box_hit(obj,v,"y")
obj.y=obj.newy 
obj.sy=(scale_y(obj.y-obj.h))

end
end

for v in all(things) do
if v!=obj then
--check collision of new horizontal
-- box_hit(obj,v,"x")
obj.x=obj.newx
obj.sx=(scale_x(obj.x-obj.w))
end
end
end

function animate(obj)
obj.s+=(abs(obj.dx)/3)
if obj.s>4 then obj.s=0 end    
if obj.dx>0 then obj.flp=false elseif obj.dx<0 then obj.flp=true end
end 

function _init()

camera_x=0
camera_y=0

--used as camera zoom
pixels=1

--create table for objects
things={}

--make objects
function make_thing(x,y
,w,h,clr,g,f,s)
thing={

x = x,-- horizontal position
y = y,-- vertical position
w = w,-- width
h   = h,--  height
dx  = 0,-- horizontal movement
dy  = 0,--  vertical movement  
sx  = x,--scaled/offset to draw
sy  = y,--scaled/offset to draw     
max_dx=2, -- max horizontal speed
max_dy=2, -- max vertical speed
acc=0.5, -- acceleration
boost=6, -- boost when jump
colour=clr,
gravity=g,
friction=f,
s=s,
flp=true
}

--add object to things table
add(things,thing)

return thing
end

--make player
pl=make_thing(64,64,4,4,1,0.3,
0.95,64)

--make some npcs
for i=1,16 do
make_thing(flr(64+cos(i/16)*25),
64+(sin(i/16)*25),4,4,i,0.3,1,
64)

end
end

function _update()

--move and animate
for v in all(things) do 
move(v)
animate(v)
end

--update camera
camera_x=(pl.x-64)
camera_y=(pl.y-64) 

--zoom in and out
if btn(4)  then 
pixels=pixels*1.1 end
if btn(5)  then 
pixels=pixels*0.9 end

end

function _draw()
cls(7)
camera(camera_x,camera_y)

--draw sprites based on 
--sx and sy

for v in all(things) do
                pal()
    sspr( flr(v.s)*8, 
    32, 
    8, 
    8, 
    (v.x)-v.w,
    (v.y)-v.h,
    (v.w*2),
    (v.h*2),
    v.flp)

    pal(1,12)
    sspr( flr(v.s)*8, 
    32, 
    8, 
    8, 
    (v.sx),
    (v.sy),
    ((v.w*2)*pixels),
    ((v.h*2)*pixels),
    v.flp)
end

--border
rect(camera_x,camera_y,camera_x+127,camera_y+127,12)
rect(camera_x+1,camera_y+1,camera_x+126,camera_y+126,13)

end

--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