西兰花伟大炮
var canvas = document.querySelector("canvas");
var ctx = canvas.getContext("2d");
canvas.width = 800;
canvas.height = 600;
var sizeX = 50;
var sizeY = 50;
for(var i = 0;i<3;i++)
{
for(var j = 0;j<3;j++){
x = i * sizeX;
y = j * sizeY;
ctx.beginPath();
ctx.rect(x,y,sizeX-1,sizeY-1);
ctx.fillStyle = "red";
ctx.fill();
ctx.closePath();
}
}没出现黑的啊，有点神奇