Javascript 从堆栈中删除画布矩形

我有以下代码：

var stack = new Array();
var last = 0;
var pospintar=0;

function Cuadrado(pcolor,pcostat){
this.color=pcolor;
this.costat=parseInt(pcostat);
}

function pintar(){
var canvas = document.getElementById('tutorial');
// Make sure we don't execute when canvas isn't supported
if (canvas.getContext){
// use getContext to use the canvas for drawing
var ctx = canvas.getContext('2d');
// Draw shapes
//ctx.fillStyle="#ff0000";
var vCuadro=stack[last];
ctx.fillStyle=vCuadro.color;
var lado=vCuadro.costat;
ctx.fillRect(20,pospintar,lado,lado);
//ctx.strokeRect(20,posPintar,lado,lado);
}
}

function empilar(color,costat)
{
var vCuadro = new Cuadrado(color,costat);
stack[last]=vCuadro;
pintar();
var vCuadro=stack[last];
var lado=vCuadro.costat;
pospintar+=lado;
last+=1;
}
function desempilar()
{

}

函数empilar绘制的矩形大小与变量costat相同

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如何使相反的函数desempilar擦除最后绘制的矩形？

在pintar函数中，您应该清除画布，遍历堆栈数组并绘制每个正方形。在desempilar函数中，您需要从堆栈中删除最后一个元素，并将最后一个变量减少1，然后再次调用pintar

function pintar() {
    var canvas = document.getElementById('tutorial');
    if (canvas.getContext) {
        var ctx = canvas.getContext('2d');
        ctx.clearRect(0,0,canvas.width,canvas.height); // Clear canvas
        var pospintar = 0;
        for (i in stack) {
            var vCuadro=stack[i];
            ctx.fillStyle=vCuadro.color;
            var lado=vCuadro.costat;
            var pospintar += lado;
            ctx.fillRect(20,pospintar,lado,lado);
        }
   }
}

function desempilar() {
    stack.splice(last, 1);
    last--;
    pintar();
}