/*
* 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;
}
}
}