How do I zoom on a canvas?

Question

I'm fairly new to Javascript and HTML5, and I'm trying to figure out how to zoom on a canvas. Let's say my Javascript code looks like this:

window.addEventListener('load', function() {
            var theCanvas = document.getElementById('myCanvas');
            theCanvas.style.border = "black 1px solid";
            if(theCanvas && theCanvas.getContext) {
                var context = theCanvas.getContext('2d');

                if(context) {
                    var x = 10;
                    var y = 10;
                    var z = 255;
                    var color = "rgb(0," + z + ",0)";
                    context.fillStyle = "rgb(100,0,0)";
                    for(var y = 0; y <= 290; y += 10) {

                        for(var x = 0; x <= 290; x += 10) {
                            if(z >= 1) {
                                z -= 1;
                            }
                            color = "rgb(0," + z + ",0)";

                            if(x % 20 === 0) {
                                context.fillStyle = color;
                            } else {
                                context.fillStyle = color;
                            }
                            context.fillRect(x, y, 10, 10);
                        }
                    }

                }

            }
        }, false);

In summary, this code just fills the canvas with tiled rectangles of changing color. But how would one go about zooming in and out on something like this?

Answer 1

You'll want the scale method of context .

And note that, once you've drawn something on the canvas, it can't really be zoomed or scaled — you've got to re-draw the entire canvas at the new "zoom level".