CODEWITHSUNDEEP
javascript
Jose Ramon
Jose Ramon

Reputation: 5444

FadeIn FadeOut in Html5 canvas

I ve got an canvas with an image and i want to fadein and fade out the image constantly. I ve used the above code:

<!DOCTYPE HTML>
 <html>
<head>
    <script>
        var canvas;
        var context;
        var ga = 0.0;
        var timerId = 0;
        var timerId1 = 0;

        function init()
        {
            canvas = document.getElementById("myCanvas");
            context = canvas.getContext("2d");

            timerId = setInterval("fadeIn()", 300);
            console.log(timerId);

        }

        function fadeIn()
        {
            context.clearRect(0,0, canvas.width,canvas.height);
            context.globalAlpha = ga;
            var photo = new Image();
            photo .onload = function()
            {
                context.drawImage(photo , 0, 0, 450, 500);
            };
            photo .src = "photo .jpg";

            ga = ga + 0.1;

            if (ga > 1.0)
            {
                fadeOut();
                goingUp = false;
                clearInterval(timerId);

            }
        }

        function fadeOut()
        {
            context.clearRect(0,0, canvas.width,canvas.height);
            context.globalAlpha = ga;

            var photo = new Image();
            photo .onload = function()
            {
                context.drawImage(photo , 0, 0, 450, 500);
            };
            photo .src = "photo .jpg";

            ga = ga - 0.1;

            if (ga < 0)
            {

                goingUp = false;
                clearInterval(timerId);
            }
        }
    </script>
</head>
<body onload="init()">
    <canvas height="500" width="500" id="myCanvas"></canvas>
</body>

Is it possible to insert two functions into setIntervals?? I want to trigger fadeOut after fadeIn function. How is it possible??

Upvotes: 2

Views: 25070

Answers (1)

user1693593
user1693593

Reputation:

Here is one way of doing this:

var alpha = 0,   /// current alpha value
    delta = 0.1; /// delta = speed

In the main loop then increase alpha with current alpha. When alpha has reached wither 0 or 1 reverse delta. This will create the ping-pong fade:

function loop() {

    alpha += delta;
    if (alpha <= 0 || alpha >= 1) delta = -delta;

    /// clear canvas, set alpha and re-draw image
    ctx.clearRect(0, 0, demo.width, demo.height);
    ctx.globalAlpha = alpha;
    ctx.drawImage(img, 0, 0);

    requestAnimationFrame(loop); // or use setTimeout(loop, 16) in older browsers
}

Upvotes: 7

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