Rendering polygons in pico-8

polygon.lua

-- require partials/class.lua
class.polygon = class{
  new = function(this,args)
    merge(this,{
      points = {},
      lines = {}
    })
    merge(this,args)
    this:rasterize()
  end,
  methods = {
    draw_fill = function(this,x,y,color)
      this:draw(x,y,color)
      for l in all(this.lines) do
        -- debugp(l)
        line(l[1][1]+x, l[1][2]+y, l[2][1]+x, l[2][2]+y, color)
      end
    end,
    draw = function(this,x,y,color)
      for i,c in pairs(this.points) do
        local n = this.points[i+1]
        if not n then n = this.points[1] end
        line(c[1]+x,c[2]+y,n[1]+x,n[2]+y,color)
      end
    end,
    rasterize = function(this)
      this:set_bounds()
      for x = 0, this.max_x do
        local drawing_line = false
        for y = 0, this.max_y do
          if this:contains(x, y) then
            if not drawing_line then
              drawing_line = true
              this:start_line(x,y)
            end
          elseif drawing_line then
            drawing_line = false
            this:end_line(x,y)
          end
        end
        if drawing_line then
          this:end_line(x,this.max_y)
        end
      end
    end,
    start_line = function(this, x, y)
      this.lines[#this.lines+1] = {{x,y}}
    end,
    end_line = function(this,x,y)
      this.lines[#this.lines][2] = {x,y}
    end,
    contains = function(this,x,y)
      local out, last_point = false, this.points[#this.points]
      for i, point in pairs(this.points) do
        if point[2] < y and last_point[2] >= y or last_point[2] < y and point[2] >= y then
          if point[1] + (y-point[2]) / (last_point[2] - point[2]) * (last_point[1] - point[1]) < x then
            out = not out
          end
        end
        last_point = point
      end
      return out
    end,
    transpose = function(this,x,y)
      for point in all(this.points) do
        point[1] += x
        point[2] += x
      end
    end,
    set_bounds = function(this)
      local minx, miny = this.points[1][1], this.points[1][2]
      local maxx, miny = minx, miny
      for i,c in pairs(this.points) do
        minx = min(minx,c[1])
        maxx = max(maxx,c[1])
        miny = min(miny,c[2])
        maxy = max(maxy,c[2])
      end
      local adjust, adjustx, adjusty = false, 0,0
      if minx != 0 then
        adjustx = -minx
        adjust = true
      end
      if miny != 0 then
        adjusty = -miny
        adjust = true
      end
      if adjust then
        this:transpose(adjustx,adjusty)
      end
      this.max_x = maxx+adjustx
      this.max_y = maxy+adjusty
    end,
  }
}