function slideListener(ctx, slideElement, pickerElement) {
        return function(evt) {
            evt = evt || window.event;
            var mouse = mousePosition(evt);
            ctx.h = mouse.y / slideElement.offsetHeight * 360 + hueOffset;
            ctx.s = ctx.v = 1;
            var c = hsv2rgb({
                h: ctx.h,
                s: 1,
                v: 1
            });
            pickerElement.style.backgroundColor = c.hex;
            ctx.callback && ctx.callback(c.hex, {
                h: ctx.h - hueOffset,
                s: ctx.s,
                v: ctx.v
            }, {
                r: c.r,
                g: c.g,
                b: c.b
            }, undefined, mouse);
        }
    }
Return click event handler for the slider.
Sets picker background color and calls ctx.callback if provided.