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Optimize retrieving of top|left|right|bottom properties. Add some documentation. Disable setting of properties for now.

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This commit is contained in:
Andrew Dupont 2009-11-02 23:54:25 -06:00
parent ac451d6d8f
commit 093c0cce4b
1 changed files with 178 additions and 10 deletions
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188
src/dom/layout.js
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@ -96,8 +96,115 @@
*
* A set of key/value pairs representing measurements of various
* dimensions of an element.
*
* <h4>Overview</h4>
*
* The `Element.Layout` class is a specialized way to measure elements.
* It helps mitigate:
*
* * The convoluted steps often needed to get common measurements for
* elements.
* * The tendency of browsers to report measurements in non-pixel units.
* * The quirks that lead some browsers to report inaccurate measurements.
* * The difficulty of measuring elements that are hidden.
*
* <h4>Usage</h4>
*
* Instantiate an `Element.Layout` class by passing an element into the
* constructor:
*
* var layout = new Element.Layout(someElement);
*
* You can also use [[Element.getLayout]], if you prefer.
*
* Once you have a layout object, retrieve properties using [[Hash]]'s
* familiar `get` and `set` syntax.
*
* layout.get('width'); //-> 400
* layout.get('top'); //-> 180
*
* The following are the CSS-related properties that can be retrieved.
* Nearly all of them map directly to their property names in CSS. (The
* only exception is for borders — e.g., `border-width` instead of
* `border-left-width`.)
*
* * `height`
* * `width`
* * `top`
* * `left`
* * `right`
* * `bottom`
* * `border-left`
* * `border-right`
* * `border-top`
* * `border-bottom`
* * `padding-left`
* * `padding-right`
* * `padding-top`
* * `padding-bottom`
* * `margin-top`
* * `margin-bottom`
* * `margin-left`
* * `margin-right`
*
* In addition, these "composite" properties can be retrieved:
*
* * `padding-box-width` (width of the content area, from the beginning of
* the left padding to the end of the right padding)
* * `padding-box-height` (height of the content area, from the beginning
* of the top padding to the end of the bottom padding)
* * `border-box-width` (width of the content area, from the outer edge of
* the left border to the outer edge of the right border)
* * `border-box-height` (height of the content area, from the outer edge
* of the top border to the outer edge of the bottom border)
* * `margin-box-width` (width of the content area, from the beginning of
* the left margin to the end of the right margin)
* * `margin-box-height` (height of the content area, from the beginning
* of the top margin to the end of the bottom margin)
*
* <h4>Caching</h4>
*
* Because these properties can be costly to retrieve, `Element.Layout`
* behaves differently from an ordinary [[Hash]].
*
* First: by default, values are "lazy-loaded" — they aren't computed
* until they're retrieved. To measure all properties at once, pass
* a second argument into the constructor:
*
* var layout = new Element.Layout(someElement, true);
*
* Second: once a particular value is computed, it's cached. Asking for
* the same property again will return the original value without
* re-computation. This means that **an instance of `Element.Layout`
* becomes stale when the element's dimensions change**. When this
* happens, obtain a new instance.
*
* <h4>Hidden elements<h4>
*
* Because it's a common case to want the dimensions of a hidden element
* (e.g., for animations), it's possible to measure elements that are
* hidden with `display: none`.
*
* However, **it's only possible to measure a hidden element if its parent
* is visible**. If its parent (or any other ancestor) is hidden, any
* width and height measurements will return `0`, as will measurements for
* `top|bottom|left|right`.
*
**/
Element.Layout = Class.create(Hash, {
/**
* new Element.Layout(element[, preCompute])
* - element (Element): The element to be measured.
* - preCompute (Boolean): Whether to compute all values at once.
*
* Declare a new layout hash.
*
* The `preCompute` argument determines whether measurements will be
* lazy-loaded or not. If you plan to use many different measurements,
* it's often more performant to pre-compute, as it minimizes the
* amount of overhead needed to measure. If you need only one or two
* measurements, it's probably not worth it.
**/
initialize: function($super, element, preCompute) {
$super();
this.element = $(element);
@ -125,14 +232,25 @@
return Hash.prototype.set.call(this, property, value);
},
// TODO: Investigate.
set: function(property, value) {
if (Element.Layout.COMPOSITE_PROPERTIES.include(property)) {
throw "Cannot set a composite property.";
}
return this._set(property, toCSSPixels(value));
throw "Properties of Element.Layout are read-only.";
// if (Element.Layout.COMPOSITE_PROPERTIES.include(property)) {
// throw "Cannot set a composite property.";
// }
//
// return this._set(property, toCSSPixels(value));
},
/**
* Element.Layout#get(property) -> Number
* - property (String): One of the properties defined in
* [[Element.Layout.PROPERTIES]].
*
* Retrieve the measurement specified by `property`. Will throw an error
* if the property is invalid.
**/
get: function($super, property) {
// Try to fetch from the cache.
var value = $super(property);
@ -228,9 +346,20 @@
Object.extend(Element.Layout, {
// All measurable properties.
/**
* Element.Layout.PROPERTIES = Array
*
* A list of all measurable properties.
**/
PROPERTIES: $w('height width top left right bottom border-left border-right border-top border-bottom padding-left padding-right padding-top padding-bottom margin-top margin-bottom margin-left margin-right padding-box-width padding-box-height border-box-width border-box-height margin-box-width margin-box-height'),
// Sums of other properties. Can be read but not written.
/**
* Element.Layout.COMPOSITE_PROPERTIES = Array
*
* A list of all composite properties. Composite properties don't map
* directly to CSS properties — they're combinations of other
* properties.
**/
COMPOSITE_PROPERTIES: $w('padding-box-width padding-box-height margin-box-width margin-box-height border-box-width border-box-height'),
COMPUTATIONS: {
@ -313,19 +442,37 @@
},
'top': function(element) {
return getPixelValue(element, 'top');
var offset = element.positionedOffset();
return offset.top;
},
'bottom': function(element) {
return getPixelValue(element, 'bottom');
var offset = element.positionedOffset(),
parent = element.getOffsetParent(),
pHeight = parent.measure('height');
var mHeight = this.get('border-box-height');
return pHeight - mHeight - offset.top;
//
// return getPixelValue(element, 'bottom');
},
'left': function(element) {
return getPixelValue(element, 'left');
var offset = element.positionedOffset();
return offset.left;
},
'right': function(element) {
return getPixelValue(element, 'right');
var offset = element.positionedOffset(),
parent = element.getOffsetParent(),
pWidth = parent.measure('width');
var mWidth = this.get('border-box-width');
return pWidth - mWidth - offset.left;
//
// return getPixelValue(element, 'right');
},
'padding-top': function(element) {
@ -382,6 +529,27 @@
}
});
// An easier way to compute right and bottom offsets.
if ('getBoundingClientRect' in document.documentElement) {
Object.extend(Element.Layout.COMPUTATIONS, {
'right': function(element) {
var parent = hasLayout(element.getOffsetParent());
var rect = element.getBoundingClientRect(),
pRect = parent.getBoundingClientRect();
return (pRect.right - rect.right).round();
},
'bottom': function(element) {
var parent = hasLayout(element.getOffsetParent());
var rect = element.getBoundingClientRect(),
pRect = parent.getBoundingClientRect();
return (pRect.bottom - rect.bottom).round();
}
});
}
/**
* class Element.Offset
*