https://openjdk.java.net/projects/openjfx/javafx-graphics/: OpenJFX JavaFX
  • OpenJFX Mailing List 
/*
 * Copyright (c) 2012, 2018, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package javafx.scene.canvas;

import javafx.beans.property.DoubleProperty;
import javafx.beans.property.DoublePropertyBase;
import javafx.geometry.NodeOrientation;
import javafx.scene.Node;
import com.sun.javafx.geom.BaseBounds;
import com.sun.javafx.geom.RectBounds;
import com.sun.javafx.geom.transform.BaseTransform;
import com.sun.javafx.scene.DirtyBits;
import com.sun.javafx.scene.NodeHelper;
import com.sun.javafx.scene.canvas.CanvasHelper;
import com.sun.javafx.sg.prism.GrowableDataBuffer;
import com.sun.javafx.sg.prism.NGCanvas;
import com.sun.javafx.sg.prism.NGNode;


Canvas is an image that can be drawn on using a set of graphics commands provided by a GraphicsContext. 
 A Canvas node is constructed with a width and height that specifies the size of the image into which the canvas drawing commands are rendered. All drawing operations are clipped to the bounds of that image. 


Example:


import javafx.scene.*;
import javafx.scene.paint.*;
import javafx.scene.canvas.*;
Group root = new Group();
Scene s = new Scene(root, 300, 300, Color.BLACK);
final Canvas canvas = new Canvas(250,250);
GraphicsContext gc = canvas.getGraphicsContext2D();
gc.setFill(Color.BLUE);
gc.fillRect(75,75,100,100);
root.getChildren().add(canvas);



See Also:
Since:JavaFX 2.2
/**
 * {@code Canvas} is an image that can be drawn on using a set of graphics
 * commands provided by a {@link GraphicsContext}.
 *
 * <p>
 * A {@code Canvas} node is constructed with a width and height that specifies the size
 * of the image into which the canvas drawing commands are rendered. All drawing
 * operations are clipped to the bounds of that image.
 * </p>
 *
 * <p>Example:</p>
 *
 * <pre>
import javafx.scene.*;
import javafx.scene.paint.*;
import javafx.scene.canvas.*;

Group root = new Group();
Scene s = new Scene(root, 300, 300, Color.BLACK);

final Canvas canvas = new Canvas(250,250);
GraphicsContext gc = canvas.getGraphicsContext2D();

gc.setFill(Color.BLUE);
gc.fillRect(75,75,100,100);

root.getChildren().add(canvas);
 * </pre>
 *
 * @see GraphicsContext
 * @since JavaFX 2.2
 */
public class Canvas extends Node {
    static {
        CanvasHelper.setCanvasAccessor(new CanvasHelper.CanvasAccessor() {
            @Override
            public NGNode doCreatePeer(Node node) {
                return ((Canvas) node).doCreatePeer();
            }

            @Override
            public void doUpdatePeer(Node node) {
                ((Canvas) node).doUpdatePeer();
            }

            @Override
            public BaseBounds doComputeGeomBounds(Node node,
                    BaseBounds bounds, BaseTransform tx) {
                return ((Canvas) node).doComputeGeomBounds(bounds, tx);
            }

            @Override
            public boolean doComputeContains(Node node, double localX, double localY) {
                return ((Canvas) node).doComputeContains(localX, localY);
            }
        });
    }
    static final int DEFAULT_VAL_BUF_SIZE = 1024;
    static final int DEFAULT_OBJ_BUF_SIZE = 32;
    private static final int SIZE_HISTORY = 5;

    private GrowableDataBuffer current;
    private boolean rendererBehind;
    private int recentvalsizes[];
    private int recentobjsizes[];
    private int lastsizeindex;

    private GraphicsContext theContext;

    {
        // To initialize the class helper at the begining each constructor of this class
        CanvasHelper.initHelper(this);
    }

    
Creates an empty instance of Canvas.

/**
     * Creates an empty instance of Canvas.
     */
    public Canvas() {
        this(0, 0);
    }

    
Creates a new instance of Canvas with the given size.

Params:
  • width – width of the canvas
  • height – height of the canvas
/**
     * Creates a new instance of Canvas with the given size.
     *
     * @param width width of the canvas
     * @param height height of the canvas
     */
    public Canvas(double width, double height) {
        this.recentvalsizes = new int[SIZE_HISTORY];
        this.recentobjsizes = new int[SIZE_HISTORY];
        setNodeOrientation(NodeOrientation.LEFT_TO_RIGHT);
        setWidth(width);
        setHeight(height);
    }

    private static int max(int sizes[], int defsize) {
        for (int s : sizes) {
            if (defsize < s) defsize = s;
        }
        return defsize;
    }

    GrowableDataBuffer getBuffer() {
        NodeHelper.markDirty(this, DirtyBits.NODE_CONTENTS);
        NodeHelper.markDirty(this, DirtyBits.NODE_FORCE_SYNC);
        if (current == null) {
            int vsize = max(recentvalsizes, DEFAULT_VAL_BUF_SIZE);
            int osize = max(recentobjsizes, DEFAULT_OBJ_BUF_SIZE);
            current = GrowableDataBuffer.getBuffer(vsize, osize);
            theContext.updateDimensions();
        }
        return current;
    }

    boolean isRendererFallingBehind() {
        return rendererBehind;
    }

    
returns the GraphicsContext associated with this Canvas. 
Returns:the GraphicsContext associated with this Canvas
/**
     * returns the {@code GraphicsContext} associated with this {@code Canvas}.
     * @return the {@code GraphicsContext} associated with this {@code Canvas}
     */
    public GraphicsContext getGraphicsContext2D() {
        if (theContext == null) {
            theContext = new GraphicsContext(this);
        }
        return theContext;
    }

    
Defines the width of the canvas.

@defaultValue0.0
/**
     * Defines the width of the canvas.
     *
     * @defaultValue 0.0
     */
    private DoubleProperty width;

    public final void setWidth(double value) {
        widthProperty().set(value);
    }

    public final double getWidth() {
        return width == null ? 0.0 : width.get();
    }

    public final DoubleProperty widthProperty() {
        if (width == null) {
            width = new DoublePropertyBase() {

                @Override
                public void invalidated() {
                    NodeHelper.markDirty(Canvas.this, DirtyBits.NODE_GEOMETRY);
                    NodeHelper.geomChanged(Canvas.this);
                    if (theContext != null) {
                        theContext.updateDimensions();
                    }
                }

                @Override
                public Object getBean() {
                    return Canvas.this;
                }

                @Override
                public String getName() {
                    return "width";
                }
            };
        }
        return width;
    }

    
Defines the height of the canvas.

@defaultValue0.0
/**
     * Defines the height of the canvas.
     *
     * @defaultValue 0.0
     */
    private DoubleProperty height;

    public final void setHeight(double value) {
        heightProperty().set(value);
    }

    public final double getHeight() {
        return height == null ? 0.0 : height.get();
    }

    public final DoubleProperty heightProperty() {
        if (height == null) {
            height = new DoublePropertyBase() {

                @Override
                public void invalidated() {
                    NodeHelper.markDirty(Canvas.this, DirtyBits.NODE_GEOMETRY);
                    NodeHelper.geomChanged(Canvas.this);
                    if (theContext != null) {
                        theContext.updateDimensions();
                    }
                }

                @Override
                public Object getBean() {
                    return Canvas.this;
                }

                @Override
                public String getName() {
                    return "height";
                }
            };
        }
        return height;
    }

    private NGNode doCreatePeer() {
        return new NGCanvas();
    }

    /*
     * Note: This method MUST only be called via its accessor method.
     */
    private void doUpdatePeer() {
        if (NodeHelper.isDirty(this, DirtyBits.NODE_GEOMETRY)) {
            NGCanvas peer = NodeHelper.getPeer(this);
            peer.updateBounds((float)getWidth(),
                              (float)getHeight());
        }
        if (NodeHelper.isDirty(this, DirtyBits.NODE_CONTENTS)) {
            NGCanvas peer = NodeHelper.getPeer(this);
            if (current != null && !current.isEmpty()) {
                if (--lastsizeindex < 0) {
                    lastsizeindex = SIZE_HISTORY - 1;
                }
                recentvalsizes[lastsizeindex] = current.writeValuePosition();
                recentobjsizes[lastsizeindex] = current.writeObjectPosition();
                rendererBehind = peer.updateRendering(current);
                current = null;
            }
        }
    }

    /*
     * Note: This method MUST only be called via its accessor method.
     */
    private boolean doComputeContains(double localX, double localY) {
        double w = getWidth();
        double h = getHeight();
        return (w > 0 && h > 0 &&
                localX >= 0 && localY >= 0 &&
                localX <  w && localY <  h);
    }

    /*
     * Note: This method MUST only be called via its accessor method.
     */
    private BaseBounds doComputeGeomBounds(BaseBounds bounds, BaseTransform tx) {
        bounds = new RectBounds(0f, 0f, (float) getWidth(), (float) getHeight());
        bounds = tx.transform(bounds, bounds);
        return bounds;
    }
}