Interacting with Canvas Rectangle

问题:

I have a canvas Element in my simple HTML page and it has few rectangles drawn using context.fillRect() method. I need to interact with these drawn rectangles.

How can I do so? How can I bind onclick or onmouseover with these rectangles?

回答1:

You'd need to keep track of the coordinates and check whether the mouse is in one of the rectangles like this: http://jsfiddle.net/eGjak/13/.

Obviously, instead of click you could also use mouseover.

var ctx = $('#cv').get(0).getContext('2d');

var rects = [[0, 0, 100, 100], [0, 150, 50, 100]]; // [x, y, width, height]
for(var i=0;i<rects.length;i++) {
    ctx.fillRect(rects[i][0], // fill at (x, y) with (width, height)
                 rects[i][1],
                 rects[i][2],
                 rects[i][3]);
}

$('#cv').click(function(e) {
    var x = e.offsetX,
        y = e.offsetY;

    for(var i=0;i<rects.length;i++) { // check whether:
        if(x > rects[i][0]            // mouse x between x and x + width
        && x < rects[i][0] + rects[i][2]
        && y > rects[i][1]            // mouse y between y and y + height
        && y < rects[i][1] + rects[i][3]) {
            alert('Rectangle ' + i + ' clicked');
        }
    }
});

回答2:

I've written a few tutorials on getting making and moving selectable shapes on Canvas that should give you a good understand of what you need.

The short answer is that you simply have to keep track of all of the things you want to select.