Implementing smooth sketching and drawing on the element

Question

I am trying to create a drawing area with canvas. I am having trouble with making the lines look smooth when drawing curves and I also have changing line thickness in my algorit

Answer 1

Have a look at this code:

http://jsfiddle.net/aMmVQ/

What I'm doing is starting a new list of points on mouseDown, then for each mousemove I add a point to the list. Once I get enough points (6 or so) I start drawing quadratic curves, with the control point of the curve being the average of the current point and the next point.

drawPoints is the bit that works this magic:

function drawPoints(ctx, points) {
    // draw a basic circle instead
    if (points.length < 6) {
        var b = points[0];
        ctx.beginPath(), ctx.arc(b.x, b.y, ctx.lineWidth / 2, 0, Math.PI * 2, !0), ctx.closePath(), ctx.fill();
        return
    }
    ctx.beginPath(), ctx.moveTo(points[0].x, points[0].y);
    // draw a bunch of quadratics, using the average of two points as the control point
    for (i = 1; i < points.length - 2; i++) {
        var c = (points[i].x + points[i + 1].x) / 2,
            d = (points[i].y + points[i + 1].y) / 2;
        ctx.quadraticCurveTo(points[i].x, points[i].y, c, d)
    }
    ctx.quadraticCurveTo(points[i].x, points[i].y, points[i + 1].x, points[i + 1].y), ctx.stroke()
}