gamera.lua

local gamera = {}

-- Private attributes and methods

local gameraMt = {__index = gamera}
local abs, min, max = math.abs, math.min, math.max

local function clamp(x, minX, maxX)
  return x < minX and minX or (x>maxX and maxX or x)
end

local function checkNumber(value, name)
  if type(value) ~= 'number' then
    error(name .. " must be a number (was: " .. tostring(value) .. ")")
  end
end

local function checkPositiveNumber(value, name)
  if type(value) ~= 'number' or value <=0 then
    error(name .. " must be a positive number (was: " .. tostring(value) ..")")
  end
end

local function checkAABB(l,t,w,h)
  checkNumber(l, "l")
  checkNumber(t, "t")
  checkPositiveNumber(w, "w")
  checkPositiveNumber(h, "h")
end

local function getVisibleArea(self, scale)
  scale = scale or self.scale
  local sin, cos = abs(self.sin), abs(self.cos)
  local w,h = self.w / scale, self.h / scale
  w,h = cos*w + sin*h, sin*w + cos*h
  return min(w,self.ww), min(h, self.wh)
end

local function cornerTransform(self, x,y)
  local scale, sin, cos = self.scale, self.sin, self.cos
  x,y = x - self.x, y - self.y
  x,y = -cos*x + sin*y, -sin*x - cos*y
  return self.x - (x/scale + self.l), self.y - (y/scale + self.t)
end

local function adjustPosition(self)
  local wl,wt,ww,wh = self.wl, self.wt, self.ww, self.wh
  local w,h = getVisibleArea(self)
  local w2,h2 = w*0.5, h*0.5

  local left, right  = wl + w2, wl + ww - w2
  local top,  bottom = wt + h2, wt + wh - h2

  self.x, self.y = clamp(self.x, left, right), clamp(self.y, top, bottom)
end

local function adjustScale(self)
  local w,h,ww,wh = self.w, self.h, self.ww, self.wh
  local rw,rh     = getVisibleArea(self, 1)      -- rotated frame: area around the window, rotated without scaling
  local sx,sy     = rw/ww, rh/wh                 -- vert/horiz scale: minimun scales that the window needs to occupy the world
  local rscale    = max(sx,sy)

  self.scale = max(self.scale, rscale)
end

-- Public interface

function gamera.new(l,t,w,h)

  local sw,sh = love.graphics.getWidth(), love.graphics.getHeight()

  local cam = setmetatable({
    x=0, y=0,
    scale=1,
    angle=0, sin=math.sin(0), cos=math.cos(0),
    l=0, t=0, w=sw, h=sh, w2=sw*0.5, h2=sh*0.5
  }, gameraMt)

  cam:setWorld(l,t,w,h)

  return cam
end

function gamera:setWorld(l,t,w,h)
  checkAABB(l,t,w,h)

  self.wl, self.wt, self.ww, self.wh = l,t,w,h

  adjustPosition(self)
end

function gamera:setWindow(l,t,w,h)
  checkAABB(l,t,w,h)

  self.l, self.t, self.w, self.h, self.w2, self.h2 = l,t,w,h, w*0.5, h*0.5

  adjustPosition(self)
end

function gamera:setPosition(x,y)
  checkNumber(x, "x")
  checkNumber(y, "y")

  self.x, self.y = x,y

  adjustPosition(self)
end

function gamera:setScale(scale)
  checkNumber(scale, "scale")

  self.scale = scale

  adjustScale(self)
  adjustPosition(self)
end

function gamera:setAngle(angle)
  checkNumber(angle, "angle")

  self.angle = angle
  self.cos, self.sin = math.cos(angle), math.sin(angle)

  adjustScale(self)
  adjustPosition(self)
end

function gamera:getWorld()
  return self.wl, self.wt, self.ww, self.wh
end

function gamera:getWindow()
  return self.l, self.t, self.w, self.h
end

function gamera:getPosition()
  return self.x, self.y
end

function gamera:getScale()
  return self.scale
end

function gamera:getAngle()
  return self.angle
end

function gamera:getVisible()
  local w,h = getVisibleArea(self)
  return self.x - w*0.5, self.y - h*0.5, w, h
end

function gamera:getVisibleCorners()
  local x,y,w2,h2 = self.x, self.y, self.w2, self.h2

  local x1,y1 = cornerTransform(self, x-w2,y-h2)
  local x2,y2 = cornerTransform(self, x+w2,y-h2)
  local x3,y3 = cornerTransform(self, x+w2,y+h2)
  local x4,y4 = cornerTransform(self, x-w2,y+h2)

  return x1,y1,x2,y2,x3,y3,x4,y4
end

function gamera:draw(f)
  love.graphics.setScissor(self:getWindow())

  love.graphics.push()
    local scale = self.scale
    love.graphics.scale(scale)

    love.graphics.translate((self.w2 + self.l) / scale, (self.h2+self.t) / scale)
    love.graphics.rotate(-self.angle)
    love.graphics.translate(-self.x, -self.y)

    f(self:getVisible())

  love.graphics.pop()

  love.graphics.setScissor()
end

function gamera:toWorld(x,y)
  local scale, sin, cos = self.scale, self.sin, self.cos
  x,y = (x - self.w2 - self.l) / scale, (y - self.h2 - self.t) / scale
  x,y = cos*x - sin*y, sin*x + cos*y
  return x + self.x, y + self.y
end

function gamera:toScreen(x,y)
  local scale, sin, cos = self.scale, self.sin, self.cos
  x,y = x - self.x, y - self.y
  x,y = cos*x + sin*y, -sin*x + cos*y
  return scale * x + self.w2 + self.l, scale * y + self.h2 + self.t
end

return gamera