How to make a canvas API colored tiles in javascript/html

Question

I want to have a program draw patterns of rectangles with random colors. I need to make random colors, using the Math object in JavaScript has a random number generator.

The pattern needs to change colors every few seconds using a setInterval function. Letting the user select the number of rows and columns to include in the pattern. Don't know where to start except:

HTML

<canvas id="myCanvas" width="300" height="150" style="border:1px solid #d3d3d3;">
    Your browser does not support the HTML5 canvas tag.
</canvas>

JavaScript:

var c=document.getElementById("myCanvas");
var ctx=c.getContext("2d");

Answer 1

You simply lay out your tiles based on rows and columns and generate a color with Math.random() for each color component:

Live demo

For example, this function will return a random color as a string which you can set directly on the fillStyle property.:

function getRandomColor() {
    return 'rgb(' +                         /// build string
        ((Math.random() * 255)|0) + ',' +   /// R component
        ((Math.random() * 255)|0) + ',' +   /// G component
        ((Math.random() * 255)|0) + ')';    /// B component
}

Then lay out the tiles:

var canvas = document.getElementById('canvas'),
    ctx = canvas.getContext('2d'),
    rows = 10,
    cols = 10,
    cw = canvas.width / cols,    /// get width of each cell
    ch = canvas.height / rows;   /// get height of each cell

function loop() {

    /// loop through rows and columns
    for(var y = 0; y < rows; y++) {
        for(var x = 0; x < cols; x++) {

            /// set random coloor
            ctx.fillStyle = getRandomColor();

            /// draw tile
            ctx.fillRect(x * cw, y * ch, cw, ch);
        }
    }
}

Now just call it once to draw then set the interval in milliseconds:

loop();
setInterval(loop, 2000); /// update every 2 seconds

Tip: There is no need for beginPath() when using fillRect() as this doesn't add anything to the path as for example rect() would.

Hope this helps!