var cam = {}

/* 
  presentation can be one of 
  letterbox
  overscan
  stretch
  ... or simply 'null' for no presentation
*/

var basecam = {
  pos: [0,0], // where it is
  ortho:true,
  width: 100,
  aspect_ratio: 16/9,
  fov:50,
  near_z:0,
  far_z:1000,
  anchor:[0.5,0.5],
  rotation:[0,0,0,1],
  presentation: "letterbox",
  background: {r:1,g:1,b:1,a:0},
  viewport: {x:0,y:0,width:1,height:1},
}

basecam.draw_rect = function(size)
{
  var mode = this.presentation || "letterbox"
  var vp = {
    x:this.viewport.x,
    y:1-this.viewport.y-this.viewport.height,
    width:this.viewport.width,
    height:this.viewport.height
  }
  var src_rect = {x:0,y:0,width:this.size.x,height:this.size.y}
  var dst_rect = {x:vp.x*size.x,y:vp.y*size.y,width:vp.width*size.x,height:vp.height*size.y};
  return mode_rect(src_rect,dst_rect,mode);
}

basecam.screen2camera = function(pos)
{
  var draw_rect = this.draw_rect(prosperon.window.size);
  var ret = [pos.x-draw_rect.x, pos.y - draw_rect.y];
  ret.x /= draw_rect.width;
  ret.y /= draw_rect.height;
  ret.y = 1 - ret.y;
  return ret;
}

basecam.screen2hud = function(pos)
{
  var cam = this.screen2camera(pos);
  cam.x *= this.size.x;
  cam.y *= this.size.y;
  return cam;
}

basecam.screen2world = function(pos)
{
  var hud = this.screen2hud(pos);
  hud.x += this.transform.pos.x - this.size.x/2;
  hud.y += this.transform.pos.y - this.size.y/2;
  return hud;
}

function mode_rect(src,dst,mode = "stretch")
{
  var aspect_src = src.width/src.height;
  var aspect_dst = dst.width/dst.height;
  var out = {
    x:dst.x,
    y:dst.y,
    width:dst.width,
    height:dst.height
  };
  if (mode == "stretch") return out;
  
  if (mode == "letterbox") {
    if (aspect_src > aspect_dst) {
      var scaled_h = out.width/aspect_src;
      var off = (out.height - scaled_h) * 0.5;
      out.y += off;
      out.height = scaled_h;
    } else {
      var scaled_w  =out.height * aspect_src;
      var off = (out.width - scaled_w) * 0.5;
      out.x += off;
      out.width = scaled_w;
    }
  } else if (mode == "overscan"){
    if (aspect_src > aspect_dst) {
      var scaled_w = out.height * aspect_src;
      var off = (out.width - scaled_w) * 0.5;
      out.x += off;
      out.width = scaled_w;
    } else {
      var scaled_h = out.width / aspect_src;
      var off = (out.height - scaled_h) * 0.5;
      out.y += off;
      out.height = scaled_h;
    }
  }
  return out;
}

cam.make = function()
{
  var c = Object.create(basecam)
  c.transform = new transform
  c.transform.unit()
  c.size = [640,360]
  c.mode = 'keep'
  c.viewport = {x:0,y:0,width:1,height:1}
  c.fov = 45
  c.type = 'ortho'
  c.ortho = true
  c.aspect = 16/9
  return c
}

return cam