diff --git a/package.json b/package.json
index f106af1..22d24f5 100644
--- a/package.json
+++ b/package.json
@@ -9,7 +9,8 @@
     "init": "lerna bootstrap --npm-client=cnpm",
     "clear": "rm -rf ./packages/*/dist/ & rm -rf ./packages/*/node_modules/",
     "jest": "jest --config jest.config.js",
-    "test": "lerna bootstrap --no-ci && npm run build && npm run jest && npm run e2e"
+    "test": "lerna bootstrap --no-ci && npm run build && npm run jest && npm run e2e",
+    "serve": "http-server ./"
   },
   "devDependencies": {
     "@babel/core": "^7.13.14",
diff --git a/packages/core/example/main.js b/packages/core/example/main.js
index 927b94a..f0ebb7b 100644
--- a/packages/core/example/main.js
+++ b/packages/core/example/main.js
@@ -9,6 +9,4 @@ const core = new Core(mount, {
   devicePixelRatio: 4
 });
 core.setData(data);
-core.draw();
-
-console.log('hello world =', Core);
\ No newline at end of file
+core.draw();
\ No newline at end of file
diff --git a/packages/core/src/index.ts b/packages/core/src/index.ts
index 6fc308c..9654cf8 100644
--- a/packages/core/src/index.ts
+++ b/packages/core/src/index.ts
@@ -1,5 +1,6 @@
 import { TypeData } from '@idraw/types';
 import Board from '@idraw/board';
+import Renderer from './lib/renderer';
 
 type Options = {
   width: number;
@@ -12,31 +13,17 @@ class Core {
   private _board: Board;
   private _data: TypeData;
   private _opts: Options;
+  private _renderer: Renderer;
 
   constructor(mount: HTMLDivElement, opts: Options) {
     this._data = { elements: [] };
     this._opts = opts;
     this._board = new Board(mount, this._opts);
+    this._renderer = new Renderer(this._board); 
   }
 
   draw() {
-    const board = this._board;
-    const ctx = board.getContext();
-    const data = this.getData();
-    const { width, height } = this._opts;
-    board.clear();
-    ctx.clearRect(0, 0, width, height);
-    ctx.setFillStyle('#ffffff');
-    ctx.fillRect(0, 0, width, height);
-    data.elements.forEach(ele => {
-      // @ts-ignore
-      if (ele.type === 'rect' && typeof ele.desc.color === 'string') {
-        // @ts-ignore
-        ctx.setFillStyle(ele.desc.color);
-      }
-      ctx.fillRect(ele.x, ele.y, ele.w, ele.h);
-    });
-    board.draw();
+    this._renderer.render(this._data);
   }
 
   getData() {
diff --git a/packages/core/src/lib/draw.ts b/packages/core/src/lib/draw.ts
new file mode 100644
index 0000000..1bcdef3
--- /dev/null
+++ b/packages/core/src/lib/draw.ts
@@ -0,0 +1,22 @@
+import { TypeContext, TypeData, TypeElement, TypeElemDesc } from '@idraw/types';
+
+export function drawContext(ctx: TypeContext, data: TypeData) {
+  for (let i = 0; i < data.elements.length; i++) {
+    const ele = data.elements[i];
+    switch (ele.type) {
+      case 'rect': {
+        drawRect<'rect'>(ctx, ele as TypeElement<'rect'>);
+      };
+      default: {
+        // nothing
+      }
+    }
+  }
+}
+
+
+function drawRect<T extends keyof TypeElemDesc>(ctx: TypeContext, ele: TypeElement<T>) {
+  const desc = ele.desc as TypeElemDesc['rect'];
+  ctx.setFillStyle(desc.color);
+  ctx.fillRect(ele.x, ele.y, ele.w, ele.h);
+}
\ No newline at end of file
diff --git a/packages/core/src/lib/renderer.ts b/packages/core/src/lib/renderer.ts
new file mode 100644
index 0000000..535417e
--- /dev/null
+++ b/packages/core/src/lib/renderer.ts
@@ -0,0 +1,21 @@
+import { TypeContext, TypeData } from '@idraw/types';
+import { drawContext } from './draw';
+import Board from '@idraw/board';
+ 
+export default class Renderer {
+
+  private _board: Board;
+  private _ctx: TypeContext;
+  private _data: TypeData = { elements: [] };
+
+  constructor(board: Board) {
+    this._board = board;
+    this._ctx = this._board.getContext();
+  }
+
+  render(data: TypeData) {
+    this._data = data;
+    drawContext(this._ctx, this._data);
+    this._board.draw();
+  }
+}
\ No newline at end of file
diff --git a/packages/core/src/util/color.ts b/packages/core/src/util/color.ts
new file mode 100644
index 0000000..4de9f98
--- /dev/null
+++ b/packages/core/src/util/color.ts
@@ -0,0 +1,7 @@
+export function toColorHexNum(color: string): number {
+  return parseInt(color.replace(/^\#/, '0x'));
+}
+
+export function toColorHexStr(color: number): string {
+  return '#' + color.toString(16);
+}
\ No newline at end of file
diff --git a/packages/core/src/util/file.ts b/packages/core/src/util/file.ts
new file mode 100644
index 0000000..30b4ce5
--- /dev/null
+++ b/packages/core/src/util/file.ts
@@ -0,0 +1,16 @@
+
+type ImageType = 'image/jpeg' | 'image/png';
+
+export function downloadImageFromCanvas (
+  canvas: HTMLCanvasElement, 
+  opts: { filename: string, type: ImageType }
+) {
+  const { filename, type = 'image/jpeg' } = opts;
+  const stream = canvas.toDataURL(type);
+  const downloadLink = document.createElement('a');
+  downloadLink.href = stream;
+  downloadLink.download = filename;
+  const downloadClickEvent = document.createEvent('MouseEvents');
+  downloadClickEvent.initEvent('click', true, false);
+  downloadLink.dispatchEvent(downloadClickEvent);
+}
\ No newline at end of file
diff --git a/packages/core/src/util/index.ts b/packages/core/src/util/index.ts
new file mode 100644
index 0000000..b99a113
--- /dev/null
+++ b/packages/core/src/util/index.ts
@@ -0,0 +1,22 @@
+import { loadImage } from './loader';
+import { delay, compose, throttle } from './time';
+import { downloadImageFromCanvas } from './file';
+import { toColorHexStr, toColorHexNum } from './color';
+
+export default {
+  time: {
+    delay,
+    compose,
+    throttle,
+  },
+  loader: {
+    loadImage
+  },
+  file: {
+    downloadImageFromCanvas,
+  },
+  color: {
+    toColorHexStr,
+    toColorHexNum,
+  }
+}
\ No newline at end of file
diff --git a/packages/core/src/util/loader.ts b/packages/core/src/util/loader.ts
new file mode 100644
index 0000000..7eedec1
--- /dev/null
+++ b/packages/core/src/util/loader.ts
@@ -0,0 +1,13 @@
+
+
+export function loadImage(src: string): Promise<HTMLImageElement> {
+  return new Promise((resolve, reject) => {
+    const img = new Image;
+    img.onload = function() {
+      resolve(img);
+    };
+    img.onabort = reject;
+    img.onerror = reject;
+    img.src = src;
+  });
+}
\ No newline at end of file
diff --git a/packages/core/src/util/time.ts b/packages/core/src/util/time.ts
new file mode 100644
index 0000000..8ec52e6
--- /dev/null
+++ b/packages/core/src/util/time.ts
@@ -0,0 +1,44 @@
+
+export function compose (middleware: Function[]) {
+  return function (context: any, next?: Function) {
+    // let index = -1;
+    return dispatch(0);
+
+    function dispatch (i: number): Promise<any> {
+      // index = i
+      let fn = middleware[i]
+      if (i === middleware.length && next) {
+        fn = next;
+      }
+      if (!fn) return Promise.resolve()
+      try {
+        return Promise.resolve(fn(context, dispatch.bind(null, i + 1)));
+      } catch (err) {
+        return Promise.reject(err)
+      }
+    }
+  }
+}
+
+
+export function delay(time: number): Promise<void> {
+  return new Promise((resolve) => {
+    setTimeout(() => {
+      resolve();
+    }, time);
+  })
+}
+
+export function throttle(fn: Function, timeout: number) {
+  let timer: any = -1;
+  return function(...args: any[]) {
+    if (timer > 0) {
+      return;
+    }
+    timer = setTimeout(() => {
+      fn(...args);
+      timer = -1;
+    }, timeout)
+  }
+}
+
diff --git a/packages/types/src/lib/data.ts b/packages/types/src/lib/data.ts
index 0ae7f18..9bc0144 100644
--- a/packages/types/src/lib/data.ts
+++ b/packages/types/src/lib/data.ts
@@ -1,21 +1,12 @@
-import { TypeElementsDesc } from './element';
+import { TypeElemDesc, TypeElement } from './element';
+
 
-type TypeDataElement<T extends keyof TypeElementsDesc> = {
-  uuid?: string;
-  x: number;
-  y: number;
-  w: number;
-  h: number;
-  type: T;
-  desc: TypeElementsDesc[T];
-}
 
 type TypeData = {
-  elements: TypeDataElement<keyof TypeElementsDesc>[]
+  elements: TypeElement<keyof TypeElemDesc>[]
   selectedElements?: string[] // uuids
 }
 
 export {
-  TypeDataElement,
   TypeData
 }
\ No newline at end of file
diff --git a/packages/types/src/lib/element.ts b/packages/types/src/lib/element.ts
index b3ac809..b9ce722 100644
--- a/packages/types/src/lib/element.ts
+++ b/packages/types/src/lib/element.ts
@@ -1,6 +1,16 @@
 import { TypePaintData } from './paint';
 
-type TypeElementsDesc = {
+type TypeElement<T extends keyof TypeElemDesc> = {
+  uuid?: string;
+  x: number;
+  y: number;
+  w: number;
+  h: number;
+  type: T;
+  desc: TypeElemDesc[T];
+}
+
+type TypeElemDesc = {
   text: TypeElemDescText,
   rect: TypeElemDescRect,
   circle: TypeElemDescCircle,
@@ -33,5 +43,6 @@ export {
   TypeElemDescText,
   TypeElemDescRect,
   TypeElemDescCircle,
-  TypeElementsDesc,
+  TypeElemDesc,
+  TypeElement,
 }
\ No newline at end of file