org.rstudio.core.client.widget.FontDetector.java Source code

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Here is the source code for org.rstudio.core.client.widget.FontDetector.java

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/*
 * FontDetector.java
 *
 * Copyright (C) 2009-12 by RStudio, Inc.
 *
 * Unless you have received this program directly from RStudio pursuant
 * to the terms of a commercial license agreement with RStudio, then
 * this program is licensed to you under the terms of version 3 of the
 * GNU Affero General Public License. This program is distributed WITHOUT
 * ANY EXPRESS OR IMPLIED WARRANTY, INCLUDING THOSE OF NON-INFRINGEMENT,
 * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Please refer to the
 * AGPL (http://www.gnu.org/licenses/agpl-3.0.txt) for more details.
 *
 */

package org.rstudio.core.client.widget;

import org.rstudio.core.client.Debug;

import com.google.gwt.canvas.client.Canvas;
import com.google.gwt.canvas.dom.client.Context2d;
import com.google.gwt.dom.client.Style.Overflow;
import com.google.gwt.dom.client.Style.Unit;
import com.google.gwt.dom.client.Style.Visibility;
import com.google.gwt.user.client.ui.RootPanel;
import com.google.gwt.user.client.ui.SimplePanel;

public class FontDetector {
    public static boolean isFontSupported(String fontName) {
        SimplePanel panel = null;
        try {
            // default font name as a reference point
            final String defaultFontName = "Arial";
            if (defaultFontName.equals(fontName))
                return true;

            // make sure canvas is supported
            if (!Canvas.isSupported())
                return false;

            // add a temporary div to the dom
            panel = new SimplePanel();
            panel.setHeight("200px");
            panel.getElement().getStyle().setVisibility(Visibility.HIDDEN);
            panel.getElement().getStyle().setOverflow(Overflow.SCROLL);
            RootPanel.get().add(panel, -2000, -2000);

            // add a canvas element to the div and get the 2d drawing context
            final Canvas canvas = Canvas.createIfSupported();
            canvas.setWidth("512px");
            canvas.setHeight("64px");
            canvas.getElement().getStyle().setLeft(400, Unit.PX);
            canvas.getElement().getStyle().setBackgroundColor("#ffe");
            panel.add(canvas);
            final Context2d ctx = canvas.getContext2d();
            ctx.setFillStyle("#000000");

            // closure to generate a hash for a font
            class HashGenerator {
                public String getHash(String fontName) {
                    ctx.setFont("57px " + fontName + ", " + defaultFontName);
                    int width = canvas.getOffsetWidth();
                    int height = canvas.getOffsetHeight();
                    ctx.clearRect(0, 0, width, height);
                    ctx.fillText("TheQuickBrownFox", 2, 50);
                    return canvas.toDataUrl();
                }
            }
            ;

            // get hashes and compare them
            HashGenerator hashGenerator = new HashGenerator();
            String defaultHash = hashGenerator.getHash(defaultFontName);
            String fontHash = hashGenerator.getHash(fontName);
            return !defaultHash.equals(fontHash);
        } catch (Exception ex) {
            Debug.log(ex.toString());
            return false;
        } finally {
            if (panel != null)
                RootPanel.get().remove(panel);
        }
    }
}