使Html5 Canvas及其包含的图像在浏览器中响应

Question

I have a canvas object that I want to put an image in for a web application. I can get the image loaded, but I've run into 2 problems: The image won't stretch to the canvas, and the canvas won't stretch to cover the entire div in any browser but Firefox.

http://jsfiddle.net/LFJ59/1/

var canvas = $("#imageView");
var context = canvas.get(0).getContext("2d");

$(document).ready(drawImage());
$(window).resize(refreshCanvas());

refreshCanvas();

function refreshCanvas() {
    //canvas/context resize
    canvas.attr("width", $(window).get(0).innerWidth / 2);
    canvas.attr("height", $(window).get(0).innerHeight / 2);
    drawImage();
};

function drawImage() {
    //shadow
    context.shadowBlur = 20;
    context.shadowColor = "rgb(0,0,0)";

    //image
    var image = new Image();
    image.src = "http://www.netstate.com/states/maps/images/ca_outline.gif";
    $(image).load(function () {
        image.height = canvas.height();
        image.width = canvas.width();
        context.drawImage(image);
    });
};

Is there a solution to making the canvas responsive? Or do I just need to lock the canvas and image down to predefined sizes?

Answer 1

width and height of image are read-only so that won't work.

Try instead:

 context.drawImage(image, 0, 0, canvas.width, canvas.height);

This will draw the image the same dimension as the canvas is (you don't need to reload the image every time btw. - just load it once globally and reuse the image variable.)

Answer 2

<canvas id="imageView" width="1000" height="1000" style="width:100%; height:100%"></canvas>

Both CSS and height and width attributes can be used and do not need to agree in size. The CSS style will determine the displayed size, you asked for a canvas that can stretch. The width and height control the number of pixels the canvas uses for drawing.

for example this will be scaled 10 to 1, and with anti-aliasing scrolling an drawing in this canvas would be as smooth as silk.

<canvas id="imageView" width="1000" height="1000" style="width:100px; height:100px"></canvas>

If CSS is not used, their defaults will be the width and height attributes of the canvas element.