com.google.gwt.canvas.client.Canvas.java Source code

Introduction

Here is the source code for com.google.gwt.canvas.client.Canvas.java

Source

/*
 * 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 com.google.gwt.canvas.client;

import com.google.gwt.canvas.dom.client.Context;
import com.google.gwt.canvas.dom.client.Context2d;
import com.google.gwt.core.client.GWT;
import com.google.gwt.dom.client.CanvasElement;
import com.google.gwt.dom.client.Document;
import com.google.gwt.dom.client.PartialSupport;
import com.google.gwt.user.client.ui.FocusWidget;

/**
 * A widget representing a <canvas> element.
 * 
 * This widget may not be supported on all browsers.
 */
@PartialSupport
public class Canvas extends FocusWidget {
    private static CanvasElementSupportDetector detector;

    /**
     * Return a new {@link Canvas} if supported,  and null otherwise.
     * 
     * @return a new {@link Canvas} if supported, and null otherwise
     */
    public static Canvas createIfSupported() {
        if (detector == null) {
            detector = GWT.create(CanvasElementSupportDetector.class);
        }
        if (!detector.isSupportedCompileTime()) {
            return null;
        }
        CanvasElement element = Document.get().createCanvasElement();
        if (!detector.isSupportedRunTime(element)) {
            return null;
        }
        return new Canvas(element);
    }

    /**
     * Runtime check for whether the canvas element is supported in this browser.
     * 
     * @return whether the canvas element is supported
     */
    public static boolean isSupported() {
        if (detector == null) {
            detector = GWT.create(CanvasElementSupportDetector.class);
        }
        if (!detector.isSupportedCompileTime()) {
            return false;
        }
        CanvasElement element = Document.get().createCanvasElement();
        if (!detector.isSupportedRunTime(element)) {
            return false;
        }
        return true;
    }

    /**
     * Protected constructor. Use {@link #createIfSupported()} to create a Canvas.
     */
    private Canvas(CanvasElement element) {
        setElement(element);
    }

    /**
     * Returns the attached Canvas Element.
     * 
     * @return the Canvas Element
     */
    public CanvasElement getCanvasElement() {
        return this.getElement().cast();
    }

    /**
     * Gets the rendering context that may be used to draw on this canvas.
     * 
     * @param contextId the context id as a String
     * @return the canvas rendering context
     */
    public Context getContext(String contextId) {
        return getCanvasElement().getContext(contextId);
    }

    /**
     * Returns a 2D rendering context.
     * 
     * This is a convenience method, see {@link #getContext(String)}.
     * 
     * @return a 2D canvas rendering context
     */
    public Context2d getContext2d() {
        return getCanvasElement().getContext2d();
    }

    /**
     * Gets the height of the internal canvas coordinate space.
     * 
     * @return the height, in pixels
     * @see #setCoordinateSpaceHeight(int)
     */
    public int getCoordinateSpaceHeight() {
        return getCanvasElement().getHeight();
    }

    /**
     * Gets the width of the internal canvas coordinate space.
     * 
     * @return the width, in pixels
     * @see #setCoordinateSpaceWidth(int)
     */
    public int getCoordinateSpaceWidth() {
        return getCanvasElement().getWidth();
    }

    /**
     * Sets the height of the internal canvas coordinate space.
     * 
     * @param height the height, in pixels
     * @see #getCoordinateSpaceHeight()
     */
    public void setCoordinateSpaceHeight(int height) {
        getCanvasElement().setHeight(height);
    }

    /**
     * Sets the width of the internal canvas coordinate space.
     * 
     * @param width the width, in pixels
     * @see #getCoordinateSpaceWidth()
     */
    public void setCoordinateSpaceWidth(int width) {
        getCanvasElement().setWidth(width);
    }

    /**
     * Returns a data URL for the current content of the canvas element.
     * 
     * @return a data URL for the current content of this element.
     */
    public String toDataUrl() {
        return getCanvasElement().toDataUrl();
    }

    /**
     * Returns a data URL for the current content of the canvas element, with a
     * specified type.
     * 
     * @param type the type of the data url, e.g., image/jpeg or image/png.
     * @return a data URL for the current content of this element with the
     *         specified type.
     */
    public String toDataUrl(String type) {
        return getCanvasElement().toDataUrl(type);
    }

    /**
     * Detector for browser support of {@link CanvasElement}.
     */
    private static class CanvasElementSupportDetector {
        /**
         * Using a run-time check, return true if the {@link CanvasElement} is 
         * supported.
         * 
         * @return true if supported, false otherwise.
         */
        static native boolean isSupportedRunTime(CanvasElement element) /*-{
                                                                        return !!element.getContext;
                                                                        }-*/;

        /**
         * Using a compile-time check, return true if {@link CanvasElement} might 
         * be supported.
         * 
         * @return true if might be supported, false otherwise.
         */
        boolean isSupportedCompileTime() {
            // will be true in CanvasElementSupportDetectedMaybe
            // will be false in CanvasElementSupportDetectedNo
            return false;
        }
    }

    /**
     * Detector for permutations that might support {@link CanvasElement}.
     */
    @SuppressWarnings("unused")
    private static class CanvasElementSupportDetectedMaybe extends CanvasElementSupportDetector {
        /**
         * Using a compile-time check, return true if {@link CanvasElement} might be
         * supported.
         *
         * @return true if might be supported, false otherwise.
         */
        @Override
        boolean isSupportedCompileTime() {
            return true;
        }
    }

    /**
     * Detector for permutations that do not support {@link CanvasElement}.
     */
    @SuppressWarnings("unused")
    private static class CanvasElementSupportDetectedNo extends CanvasElementSupportDetector {
        /**
         * Using a compile-time check, return true if {@link CanvasElement} might be
         * supported.
         *
         * @return true if might be supported, false otherwise.
         */
        @Override
        boolean isSupportedCompileTime() {
            return false;
        }
    }
}