Question

I have the following bit of code which is responsible for displaying a tooltip. I am unhappy with this code for two reasons:

• I use pageXOffset and pageYOffset ‘magic numbers’ to correct the visual state per-browser.
• The dialog window must remain stationary for the numbers to be correct.

I have tried binding to the dialog window’s mousemove event instead of the document. The results were identical to my current implementation which binds to document’s mousemove.

var shouldDisplay = false;
$(document).mousemove(AdjustToolTipPosition);

function DisplayTooltip(tooltip_text) {
    shouldDisplay = (tooltip_text != "") ? true : false;
    if (shouldDisplay) {
        $('#CustomTooltip').html(tooltip_text);
        $('#CustomTooltip').show();
    }
    else {
        //Sometimes the tooltip hasn't finished fading in before we ask to hide it. This causes it to hide, then fade back in.
        $('#CustomTooltip').hide();
    }
}

function AdjustToolTipPosition(e) {
    if (shouldDisplay) {
        //msie e.page event should be standardizes, but seems to go awry when working inside of a modal window.
        var pageYOffset = $.browser.msie ? 260 : 572; //-314
        var pageXOffset = $.browser.msie ? 474 : 160; //+314

        $('#CustomTooltip').css('top', e.pageY - pageYOffset + 'px');
        var offsetLeft = e.pageX - pageXOffset;
        var isOutsideViewport = $("#HistoricalChartDialog").width() - $("#CustomTooltip").width() - offsetLeft < 0;

        //Prevent the tooltip from going off the screen by changing the offset when it would go off screen.
        if (isOutsideViewport) {
            offsetLeft = $("#HistoricalChartDialog").width() - $("#CustomTooltip").width();
        }

        $('#CustomTooltip').css('left', offsetLeft + 'px');
    }
}

// Initialize the Historical Chart dialog.        
$('#HistoricalChartDialog').dialog({
    autoOpen: false,
    buttons: {
        'Close': function() {
            $(this).dialog('close');
        }
    },
    hide: 'fold',
    modal: true,
    draggable: false,
    resizable: false,
    position: 'center',
    title: 'Historical Charts',
    width: 700,
    height: 475
});

I provide the jQuery dialog initializer just for the sake of it. The tooltip only displays inside of this dialog window — but the coordinates are for the entire page. Is it possible to retrieve coordinates relative to the dialog window so that I can leverage the fact that jQuery’s mousemove standardizes coordinates with the pageX and pageY properties?

EDIT solution:

//Seperate file because the offsets are different for the image under MVC.
var shouldDisplay = false;
$("#HistoricalChartDialog").mousemove(AdjustToolTipPosition);

function DisplayTooltip(tooltip_text) {
    shouldDisplay = (tooltip_text != "") ? true : false;
    if (shouldDisplay) {
        $('#CustomTooltip').html(tooltip_text);
        $('#CustomTooltip').show();
    }
    else {
        //Sometimes the tooltip hasn't finished fading in before we ask to hide it. This causes it to hide, then fade back in.
        $('#CustomTooltip').hide();
    }
}

function AdjustToolTipPosition(e) {
    if (shouldDisplay) {
        var xPos = e.pageX - $(this).closest('.ui-dialog').offset().left + 15;
        var widthDifference = $(this).width() - $("#CustomTooltip").width();
        //Prevent the tooltip from going off the screen by changing the offset when it would go off screen.
        xPos = (widthDifference - xPos < 0) ? widthDifference : xPos;
        $('#CustomTooltip').css('left', xPos + 'px');

        var yPos = e.pageY - $(this).closest('.ui-dialog').offset().top - 10;
        $('#CustomTooltip').css('top', yPos + 'px');
    }
}

Answer 1

To get the position of the mouse relative to a specific div, not the viewport, you take the eventX/Y and subtract the left/top position of the div:

$("#example").mousemove(function(e) {
    var xPos = e.pageX - $(this).position().left;
    var yPos = e.pageY - $(this).position().top;
    $("#pos").text("x: " + xPos + " / y: " + yPos);
});

Example fiddle

Given your example, this should work. You may need to look at your isOutsideViewport logic though.

function AdjustToolTipPosition(e) {
    if (shouldDisplay) {
        var xPos = e.pageX - $(this).position().left;
        var yPos = e.pageY - $(this).position().top;

        var isOutsideViewport = $("#HistoricalChartDialog").width() - $("#CustomTooltip").width() - xPos < 0;
        if (isOutsideViewport) {
            offsetLeft = $("#HistoricalChartDialog").width() - $("#CustomTooltip").width();
        }

        $('#CustomTooltip').css({
            'top': yPos + 'px',
            'left': xPos + 'px'
        });
    }
}