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@ronmichael
Created September 6, 2013 22:01
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Get the bounding box coordinates of the actual text within an HTML input box
// http://stackoverflow.com/questions/6930578/get-cursor-or-text-position-in-pixels-for-input-element/7948715#7948715
function getTextBoundingRect(input, selectionStart, selectionEnd, debug) {
// Basic parameter validation
if (!input || !('value' in input)) return input;
if (typeof selectionStart == "string") selectionStart = parseFloat(selectionStart);
if (typeof selectionStart != "number" || isNaN(selectionStart)) {
selectionStart = 0;
}
if (selectionStart < 0) selectionStart = 0;
else selectionStart = Math.min(input.value.length, selectionStart);
if (typeof selectionEnd == "string") selectionEnd = parseFloat(selectionEnd);
if (typeof selectionEnd != "number" || isNaN(selectionEnd) || selectionEnd < selectionStart) {
selectionEnd = selectionStart;
}
if (selectionEnd < 0) selectionEnd = 0;
else selectionEnd = Math.min(input.value.length, selectionEnd);
// If available (thus IE), use the createTextRange method
if (typeof input.createTextRange == "function") {
var range = input.createTextRange();
range.collapse(true);
range.moveStart('character', selectionStart);
range.moveEnd('character', selectionEnd - selectionStart);
return range.getBoundingClientRect();
}
// createTextRange is not supported, create a fake text range
var offset = getInputOffset(),
topPos = offset.top,
leftPos = offset.left,
width = getInputCSS('width', true),
height = getInputCSS('height', true);
// Styles to simulate a node in an input field
var cssDefaultStyles = "white-space:pre;padding:0;margin:0;",
listOfModifiers = ['direction', 'font-family', 'font-size', 'font-size-adjust', 'font-variant', 'font-weight', 'font-style', 'letter-spacing', 'line-height', 'text-align', 'text-indent', 'text-transform', 'word-wrap', 'word-spacing'];
topPos += getInputCSS('padding-top', true);
topPos += getInputCSS('border-top-width', true);
leftPos += getInputCSS('padding-left', true);
leftPos += getInputCSS('border-left-width', true);
leftPos += 1; //Seems to be necessary
for (var i = 0; i < listOfModifiers.length; i++) {
var property = listOfModifiers[i];
cssDefaultStyles += property + ':' + getInputCSS(property) + ';';
}
// End of CSS variable checks
var text = input.value,
textLen = text.length,
fakeClone = document.createElement("div");
if (selectionStart > 0) appendPart(0, selectionStart);
var fakeRange = appendPart(selectionStart, selectionEnd);
if (textLen > selectionEnd) appendPart(selectionEnd, textLen);
// Styles to inherit the font styles of the element
fakeClone.style.cssText = cssDefaultStyles;
// Styles to position the text node at the desired position
fakeClone.style.position = "absolute";
fakeClone.style.top = topPos + "px";
fakeClone.style.left = leftPos + "px";
fakeClone.style.width = width + "px";
fakeClone.style.height = height + "px";
document.body.appendChild(fakeClone);
var returnValue = fakeRange.getBoundingClientRect(); //Get rect
if (!debug) fakeClone.parentNode.removeChild(fakeClone); //Remove temp
return returnValue;
// Local functions for readability of the previous code
function appendPart(start, end) {
var span = document.createElement("span");
span.style.cssText = cssDefaultStyles; //Force styles to prevent unexpected results
span.textContent = text.substring(start, end);
fakeClone.appendChild(span);
return span;
}
// Computing offset position
function getInputOffset() {
var body = document.body,
win = document.defaultView,
docElem = document.documentElement,
box = document.createElement('div');
box.style.paddingLeft = box.style.width = "1px";
body.appendChild(box);
var isBoxModel = box.offsetWidth == 2;
body.removeChild(box);
box = input.getBoundingClientRect();
var clientTop = docElem.clientTop || body.clientTop || 0,
clientLeft = docElem.clientLeft || body.clientLeft || 0,
scrollTop = win.pageYOffset || isBoxModel && docElem.scrollTop || body.scrollTop,
scrollLeft = win.pageXOffset || isBoxModel && docElem.scrollLeft || body.scrollLeft;
return {
top: box.top + scrollTop - clientTop,
left: box.left + scrollLeft - clientLeft
};
}
function getInputCSS(prop, isnumber) {
var val = document.defaultView.getComputedStyle(input, null).getPropertyValue(prop);
return isnumber ? parseFloat(val) : val;
}
}
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