用文本预渲染画布矩形，这是不好的表现吗？

Question

It is taking up to 0.300ms to complete which is at least 2X slower than just caling the function straight without pre-rendering, I think thats quite a lot... What do you guys think? Is this normal? Am I doing this right? Something must be wrong.

function complexDraw(ctx){
    ctx.fillStyle = "Black";
    ctx.fillRect(90 * Xf, 380 * Yf, 200 * Xf, 30 * Yf);//k10
    ctx.fillStyle = "White";
    ctx.font = pixels + "px monospace";
    ctx.textAlign = "center";
    ctx.fillText("Left: " + currentremain, 185 * Xf, 400 * Yf);
}

function cloneCanvas(oldCanvas) {

    //create a new canvas
    var newCanvas = document.createElement('canvas');
    var context = newCanvas.getContext('2d');

    //set dimensions
    newCanvas.width = oldCanvas.width;
    newCanvas.height = oldCanvas.height;

    //apply the old canvas to the new one
    context.drawImage(oldCanvas, 0, 0);

    //return the new canvas
    return newCanvas;
}

var cacheCanvas = cloneCanvas(a_canvas); // newCanvas
var cacheCtx = cacheCanvas.getContext('2d'); // context


var draw = function draw(){
    complexDraw(cacheCtx); //updates text each time
    ctx.drawImage(cacheCanvas,0,0);
}

console.time("new");
draw();
console.timeEnd("new")// 0.300ms

Answer 1

You are still doing the drawing on your "cache" canvas so essentially you are doing the drawing + copy. I wouldn't be surprised if it takes more then just drawing directly. Especially if your canvases are large and you have to copy loads of pixels.

Edit: Just to clarify: You do not need to implement double buffering for HTML canvas because browsers do not update canvas image on screen until your script is finished executing.