如何在循环中呈现HTML5画布

Question

I'm trting to do the following:

I'm running through a for loop and each time I get a new information and want to draw it on the canvas. The problem is that the canvas is being drawn just after the loop finish, and I can't see no animation. If I step in with debug, or with alert messages, it will draw to the canvas immediatly. How can I do it?

Here is my code, as you can see I've already tried with setTimeout in multiple ways but didn't worked.

for(var i=0;i<1000; i ++)
    {
        addLines(ga.getBestCreature());   // This method draw on the canvas 

        setTimeout(function() {
        ga.startEvolution(1);       // This method change the best creature
        }, 10);   
    }

The drowing method:

function addLines(best) {

    if(!best) {
        return;
    }
    var global_path = best.data;

    redraw(); // Clear off the canvas

    var cityA;
    var cityB;
    for (var i = 0; i < (global_path.length - 1); i++) {

        cityA = ga.cities[global_path[i]];
        cityB = ga.cities[global_path[i+1]];

        ctx.moveTo(cityA.x,cityA.y);
        ctx.lineTo(cityB.x,cityB.y);
        ctx.stroke();
    }
}

Any Ideas??

Update: After was advised to use the requestAnimationFrame, I've came out with something like this. Is this the best approuch? I'm updating a global variable called 'run' on click events

var run = 0;
function animate() {

    if(run > 0) {
        ga.startEvolution(1);
        run--;
    }

addLines(ga.getBestCreature());
    requestAnimationFrame(animate);
}

animate();

Answer 1

You could take a look at requestAnimationFrame : https://developer.mozilla.org/en-US/docs/Web/API/window/requestAnimationFrame

And us it something like this:

function loop() {
    addLines(ga.getBestCreature());

    // execute loop function over and over
    requestAnimationFrame(loop);
}

Answer 2

Your best take is to separate concerns : have an animation loop continuously running, and, "each time [you] get a new information", update your scene description, it will draw as soon as the display is ready.

So a first very simple demo : here the 'new information' is a user click.

 var cv = document.getElementById('cv'); var ctx = cv.getContext('2d'); var cvWidth = cv.width; var cvHeight = cv.height; // Simple scene description : an array of colored rects var everyObject = [ [60, 70, 30, 30, 'yellow'] ]; // animation : always running loop. function animate() { // call again next time we can draw requestAnimationFrame(animate); // clear canvas ctx.clearRect(0, 0, cvWidth, cvHeight); // draw everything everyObject.forEach(function(o) { ctx.fillStyle = o[4]; ctx.fillRect(o[0], o[1], o[2], o[3]); }); // ctx.fillStyle = '#000'; ctx.fillText('click to add random rects', 10, 10); } animate(); // click handler to add random rects window.addEventListener('click', function() { addRandRect(); }); function addRandRect() { var randColor = Math.random() > 0.5 ? 'blue' : 'red'; everyObject.push([Math.random() * cvWidth, Math.random() * cvHeight, 10 + Math.random() * 40, 10 + Math.random() * 40, randColor]); } 

 <canvas id='cv' width=400 height=200></canvas> 

Now if you want some kind of animation, or a simple version using setTimeOut would be :

 var cv = document.getElementById('cv'); var ctx = cv.getContext('2d'); var cvWidth = cv.width; var cvHeight = cv.height; // Simple scene description : an array of colored rects var everyObject = [ [60, 70, 30, 30, 'yellow'] ]; // animation : always running loop. function animate() { // call again next time we can draw requestAnimationFrame(animate); // clear canvas ctx.clearRect(0, 0, cvWidth, cvHeight); // draw everything everyObject.forEach(function(o) { ctx.fillStyle = o[4]; ctx.fillRect(o[0], o[1], o[2], o[3]); }); // ctx.fillStyle = '#000'; ctx.fillText('click to add 4 random rects with a delay', 10, 10); } animate(); // click handler to add random rects window.addEventListener('click', function() { addRandRect(); setTimeout(addRandRect, 300); setTimeout(addRandRect, 600); setTimeout(addRandRect, 900); }); function addRandRect() { var randColor = Math.random() > 0.5 ? 'blue' : 'red'; everyObject.push([Math.random() * cvWidth, Math.random() * cvHeight, 10 + Math.random() * 40, 10 + Math.random() * 40, randColor]); } 

  <canvas id='cv' width=400 height=200></canvas> 

(By the way i wrote about animation here if interested : http://codepen.io/gamealchemist/post/animationcanvas1 )