图形

createPattern(图像对象, 重复类型)

重复类型有：repeat, repeat-x, repeat-y, norepeat

let image = new Image();
image.src = '图片路径';

image.onload = function(){
  let p = ctx.createPattern(image, 'repeat');
  ctx.fillStyle = p;
  ctx.fillRect(0,0,100,100);
}