game.re

open Webapi.Dom;
open Webapi.Canvas.Canvas2d;
open Webapi.Canvas.CanvasElement;

type position = (float, float);

type shape('s, 'a) = {
  state: 's,
  reducer: ('a, 's) => 's,
  render: (shape('s, 'a)) => unit
};

let getPositionByCenterOfMass = (~r: float, pos: position): position => {
  let (x, y) = pos;

  (x +. r, y +. r);
};

type state = {
  position,
  radius: float,
};

type action =
  | Move(position);

let makeShape = (~pos, ~r, ctx: t) => {
  state: {
    position: pos,
    radius: r,
  },
  reducer: (action, state) =>
    switch (action) {
    | Move(position) => ({ ...state, position })
    },
  render: (self) => {
    let (x, y) = getPositionByCenterOfMass(~r=self.state.radius, self.state.position);

    beginPath(ctx);
    arc(
      ~x,
      ~y,
      ~r=self.state.radius,
      ~startAngle=0.0,
      ~endAngle=Js.Math._PI *. 2.0,
      ~anticw=false,
      ctx,
    );
    fill(ctx);
  }
};

let main = () => {
  let canvas =
    switch (Document.getElementById("app", document)) {
    | Some(element) => element
    | None => failwith("canvas not found")
    };

  let ctx = getContext2d(canvas);
  let player = makeShape(~pos=(0.0, 0.0), ~r=10.0, ctx);

  player.render(player);
};

main();