How to make this HTML canvas to full screen?

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I am having trouble trying to set the canvas to fill the whole window. It is currently set to 500x500.. I am new to coding and would really appreciate any help! Thank you.

Here is the code:

HTML

<html>
<head>
    <title>Starfield effect done in HTML 5</title>
    <script>
        window.onload = function() {

            /* --- config start --- */

            var starfieldCanvasId     = "starfieldCanvas", // id of the canvas to use
                framerate             = 60,                // frames per second this animation runs at (this is not exact)
                numberOfStarsModifier = 0.15,               // Number of stars, higher numbers have performance impact
                flightSpeed           = 0.003;              // speed of the flight, the higher this number the faster

            /* ---- config end ---- */

            var canvas        = document.getElementById(starfieldCanvasId),
                context       = canvas.getContext("2d"),
                width         = canvas.width,
                height        = canvas.height,
                numberOfStars = width * height / 1000 * numberOfStarsModifier,
                dirX          = width / 2,
                dirY          = height / 2,
                stars         = [],
                TWO_PI        = Math.PI * 2;

            // initialize starfield
            for(var x = 0; x < numberOfStars; x++) {
                stars[x] = {
                    x: range(0, width),
                    y: range(0, height),
                    size: range(0, 1)
                };
            }

            // when mouse moves over canvas change middle point of animation
            canvas.onmousemove = function(event) {
                dirX = event.offsetX,
                dirY = event.offsetY;
            }

            // start tick at specified fps
            window.setInterval(tick, Math.floor(1000 / framerate));

            // main routine
            function tick() {
                var oldX,
                    oldY;

                // reset canvas for next frame
                context.clearRect(0, 0, width, height);

                for(var x = 0; x < numberOfStars; x++) {
                    // save old status
                    oldX = stars[x].x;
                    oldY = stars[x].y;

                    // calculate changes to star
                    stars[x].x += (stars[x].x - dirX) * stars[x].size * flightSpeed;
                    stars[x].y += (stars[x].y - dirY) * stars[x].size * flightSpeed;
                    stars[x].size += flightSpeed;

                    // if star is out of bounds, reset
                    if(stars[x].x < 0 || stars[x].x > width || stars[x].y < 0 || stars[x].y > height) {
                        stars[x] = {
                            x: range(0, width),
                            y: range(0, height),
                            size: 0
                        };
                    }

                    // draw star
                    context.strokeStyle = "rgba(255, 255, 255, " + Math.min(stars[x].size, 1) + ")";
                    context.lineWidth = stars[x].size;
                    context.beginPath();
                    context.moveTo(oldX, oldY);
                    context.lineTo(stars[x].x, stars[x].y);
                    context.stroke();
                }
            }

            // get a random number inside a range
            function range(start, end) {
                return Math.random() * (end - start) + start;
            }
        };
    </script>
</head>
<body style="background:#000;">
    <canvas width="500" height="500" id="starfieldCanvas"></canvas>
</body>
</html>

What I have tried:

Tried a bunch of things, nothing worked.

Posted 1-Apr-17 12:49pm

Member 13099812

Updated 1-Apr-17 17:22pm

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Bryian Tan · Answer 1 · 2017-04-01T17:22:00

Solution 1

Can you define the width and height in the style?

CSS

<style>
    #starfieldCanvas {
        width:100%;
        height:100%;
    }
</style>

The canvas will end up like

HTML

<canvas id="starfieldCanvas"></canvas>

Posted 1-Apr-17 17:22pm

Bryian Tan