/**
* Copyright 2010 Google Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*/
package org.waveprotocol.wave.client.common.util;
import com.google.gwt.dom.client.Element;
/**
* Provides layout properties of elements. In particular, reveals such
* properties in fractional units, on browsers that have sub-pixel rendering.
*
*/
public final class MeasurerInstance {
/** Measuring strategy. */
private static final Measurer instance =
UserAgent.isFirefox() ? new BoundingClientRectMeasurer() : new GwtMeasurer();
/**
* @return the singleton measuring strategy.
*/
public static Measurer get() {
return instance;
}
/**
* GWT's default measuring logic.
*/
static final class GwtMeasurer implements Measurer {
@Override
public double bottom(Element base, Element e) {
return e.getAbsoluteBottom() - (base != null ? base.getAbsoluteTop() : 0);
}
@Override
public double top(Element base, Element e) {
return e.getAbsoluteTop() - (base != null ? base.getAbsoluteTop() : 0);
}
@Override
public double left(Element base, Element e) {
return e.getAbsoluteLeft() - (base != null ? base.getAbsoluteLeft() : 0);
}
@Override
public double height(Element e) {
return e.getOffsetHeight();
}
@Override
public double offsetTop(Element e) {
return e.getOffsetTop();
}
@Override
public double offsetBottom(Element e) {
return e.getOffsetTop() + e.getOffsetHeight();
}
}
/**
* A Measurer that uses getBoundingClientRect().
*/
public static final class BoundingClientRectMeasurer implements Measurer {
@Override
public native double top(Element base, Element elem) /*-{
return elem.getBoundingClientRect().top - (base ? base.getBoundingClientRect().top : 0);
}-*/;
@Override
public native double left(Element base, Element elem) /*-{
return elem.getBoundingClientRect().left - (base ? base.getBoundingClientRect().left : 0);
}-*/;
@Override
public native double bottom(Element base, Element elem) /*-{
return elem.getBoundingClientRect().bottom - (base ? base.getBoundingClientRect().top : 0);
}-*/;
@Override
public native double height(Element elem) /*-{
var rect = elem.getBoundingClientRect();
return rect.bottom - rect.top;
}-*/;
@Override
public double offsetBottom(Element e) {
return bottom(e.getOffsetParent(), e);
}
@Override
public double offsetTop(Element e) {
return top(e.getOffsetParent(), e);
}
}
}