Java tutorial
// Copyright 2012 Google Inc. All Rights Reserved. // // 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 com.google.collide.client.util.dom; import com.google.collide.client.util.CssUtils; import com.google.collide.client.util.Elements; import com.google.collide.json.shared.JsonArray; import com.google.collide.shared.util.JsonCollections; import com.google.gwt.event.logical.shared.ResizeEvent; import com.google.gwt.event.logical.shared.ResizeHandler; import com.google.gwt.user.client.Timer; import com.google.gwt.user.client.Window; import elemental.css.CSSStyleDeclaration; import elemental.html.Element; /** * A class that computes the height and width of a character. */ public class FontDimensionsCalculator { public interface FontDimensions { float getBaseWidth(); float getBaseHeight(); float getWidthZoomFactor(); float getHeightZoomFactor(); float getCharacterWidth(); float getCharacterHeight(); } private class FontDimensionsImpl implements FontDimensions { private float baseWidth; private float baseHeight; private float widthFactor = 1; private float heightFactor = 1; /** * Updates the width and height internally. If this has never been set * before this will set the baseWidth and baseHeight. Otherwise it will * adjust the zoom factor and the current character width and height. * * @return false if no update was required. */ private boolean update(float width, float height) { if (baseWidth == 0 && baseHeight == 0) { baseWidth = width; baseHeight = height; return true; } else if (baseWidth * widthFactor != width || baseHeight * heightFactor != height) { widthFactor = width / baseWidth; heightFactor = height / baseHeight; return true; } return false; } @Override public float getBaseWidth() { return baseWidth; } @Override public float getBaseHeight() { return baseHeight; } @Override public float getWidthZoomFactor() { return widthFactor; } @Override public float getHeightZoomFactor() { return heightFactor; } @Override public float getCharacterWidth() { return widthFactor * baseWidth; } @Override public float getCharacterHeight() { return heightFactor * baseHeight; } } private static final int POLLING_CUTOFF = 10000; private static final String SAMPLE_TEXT = "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"; private static final int SAMPLE_ROWS = 30; public interface Callback { void onFontDimensionsChanged(FontDimensions fontDimensions); } private static FontDimensionsCalculator INSTANCE; public static FontDimensionsCalculator get(String fontClassName) { if (INSTANCE == null) { INSTANCE = new FontDimensionsCalculator(fontClassName); } return INSTANCE; } private final Element dummyElement; /* * This timer is called during the first 12s. When using a web font it will be * loaded asynchronously and our initial measurements will be incorrect. By * polling we remeasure after this font has been loaded and updated our size. */ private final Timer repeater = new Timer() { @Override public void run() { if (pollingDelay >= POLLING_CUTOFF) { // Terminate polling rescheduling once we cross the cutoff. return; } measureAndDispatch(); schedule(pollingDelay); pollingDelay *= 2; } }; private int pollingDelay = 500; private JsonArray<Callback> callbacks = JsonCollections.createArray(); private final FontDimensionsImpl fontDimensions; private final String fontClassName; private FontDimensionsCalculator(String fontClassName) { this.fontClassName = fontClassName; // This handler will be called when the browser window zooms Window.addResizeHandler(new ResizeHandler() { @Override public void onResize(ResizeEvent arg0) { measureAndDispatch(); } }); // Build a multirow text block so we can measure it StringBuilder htmlContent = new StringBuilder(SAMPLE_TEXT); for (int i = 1; i < SAMPLE_ROWS; i++) { htmlContent.append("<br/>"); htmlContent.append(SAMPLE_TEXT); } dummyElement = Elements.createSpanElement(fontClassName); dummyElement.setInnerHTML(htmlContent.toString()); dummyElement.getStyle().setVisibility(CSSStyleDeclaration.Visibility.HIDDEN); dummyElement.getStyle().setPosition(CSSStyleDeclaration.Position.ABSOLUTE); Elements.getBody().appendChild(dummyElement); fontDimensions = new FontDimensionsImpl(); repeater.schedule(pollingDelay); /* * Force an initial measure (the dispatch won't happen since no one is * attached) */ measureAndDispatch(); } public void addCallback(final Callback callback) { callbacks.add(callback); } public void removeCallback(final Callback callback) { callbacks.remove(callback); } /** * Returns a font dimensions that will be updated as the font dimensions * change. */ public FontDimensions getFontDimensions() { return fontDimensions; } public String getFontClassName() { return fontClassName; } public String getFont() { return CssUtils.getComputedStyle(dummyElement).getPropertyValue("font"); } private void measureAndDispatch() { float curWidth = dummyElement.getOffsetWidth() / ((float) SAMPLE_TEXT.length()); float curHeight = dummyElement.getOffsetHeight() / ((float) SAMPLE_ROWS); if (fontDimensions.update(curWidth, curHeight)) { dispatchToCallbacks(); } } private void dispatchToCallbacks() { for (int i = 0, n = callbacks.size(); i < n; i++) { callbacks.get(i).onFontDimensionsChanged(fontDimensions); } } }