annis.gui.components.ScreenshotMaker.java Source code

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Here is the source code for annis.gui.components.ScreenshotMaker.java

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/*
 * Copyright 2013 Corpuslinguistic working group Humboldt University Berlin.
 *
 * 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 annis.gui.components;

import com.vaadin.annotations.JavaScript;
import com.vaadin.server.AbstractJavaScriptExtension;
import com.vaadin.server.ClientConnector;
import com.vaadin.ui.JavaScriptFunction;
import com.vaadin.ui.UI;
import elemental.json.JsonArray;
import org.apache.commons.codec.binary.Base64;
import org.apache.commons.lang3.Validate;
import org.json.JSONException;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * A component that can make pure JavaScript based "screenshots".
 * 
 * Uses the http://html2canvas.hertzen.com/ library.
 * @author Thomas Krause <krauseto@hu-berlin.de>
 */
@JavaScript({ "vaadin://jquery.js", "html2canvas.js", "screenshotmaker.js" })
public class ScreenshotMaker extends AbstractJavaScriptExtension {
    private static final Logger log = LoggerFactory.getLogger(ScreenshotMaker.class);

    public ScreenshotMaker(final ScreenshotCallback callback) {
        Validate.notNull(callback);

        addFunction("finishedScreenshot", new JavaScriptFunction() {
            @Override
            public void call(JsonArray arguments) throws JSONException {
                parseAndCallback(arguments.getString(0), callback);
            }
        });
    }

    @Override
    protected Class<? extends ClientConnector> getSupportedParentType() {
        return UI.class;
    }

    /**
     * Takes a raw string representing the result of the toDataURL() function
     * of the HTML5 canvas and calls the callback with a proper mime type 
     * and the bytes of the image.
     * 
     * @see  <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#dom-canvas-todataurl">http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#dom-canvas-todataurl</
     * @param rawImage The encoded image
     * @param callback The callback to call with the result.
     * @return 
     */
    private void parseAndCallback(String rawImage, ScreenshotCallback callback) {
        if (callback == null) {
            return;
        }

        // find the mime type
        final String[] typeInfoAndData = rawImage.split(",");
        String[] mimeAndEncoding = typeInfoAndData[0].replaceFirst("data:", "").split(";");
        if (typeInfoAndData.length == 2 && mimeAndEncoding.length == 2
                && "base64".equalsIgnoreCase(mimeAndEncoding[1])) {
            byte[] result = Base64.decodeBase64(typeInfoAndData[1]);
            callback.screenshotReceived(result, mimeAndEncoding[0]);
        }

    }

    public void makeScreenshot() {
        callFunction("makeScreenshot");
    }

    public static interface ScreenshotCallback {
        /**
         * Called whenever new data is available.
         * 
         * @param imageData The image as raw PNG data.
         */
        public void screenshotReceived(byte[] imageData, String mimeType);
    }
}