image.java

用于移动设备上的java虚拟机源代码

/*
 * @(#)Image.java	1.52 02/09/06 @(#)
 *
 * Copyright (c) 1999-2002 Sun Microsystems, Inc.  All rights reserved.
 * PROPRIETARY/CONFIDENTIAL
 * Use is subject to license terms.
 */

package javax.microedition.lcdui;

import java.io.InputStream;
import java.io.IOException;
import javax.microedition.lcdui.game.Sprite;

/**
 * The <code>Image</code> class is used to hold graphical image
 * data. <code>Image</code>
 * objects exist independently of the display device. They exist only in
 * off-screen memory and will not be painted on the display unless an explicit
 * command is issued by the application (such as within the
 * <code>paint()</code> method of
 * a <code>Canvas</code>) or when an <code>Image</code> object is
 * placed within a <code>Form</code> screen or an
 * <code>Alert</code> screen and that screen is made current.
 *
 * <p>Images are either <em>mutable</em> or <em>immutable</em> depending upon
 * how they are created. Immutable images are generally created by loading
 * image data from resource bundles, from files, or from the network. They may
 * not be modified once created. Mutable images are created as blank images
 * containing only white pixels. The application may render on a mutable image
 * by calling {@link #getGraphics} on the <code>Image</code> to obtain
 * a <code>Graphics</code> object
 * expressly for this purpose.</p>
 *
 * <p><code>Images</code> may be placed within <code>Alert</code>,
 * <code>Choice</code>, <code>Form</code>, or <code>ImageItem</code>
 * objects.
 * The high-level user interface implementation may need to update the display
 * at any time, without notifying the application.  In order to provide
 * predictable behavior, the high-level user interface
 * objects provide snapshot semantics for the image.  That is, when a mutable
 * image is placed within an <code>Alert</code>, <code>Choice</code>,
 * <code>Form</code>, or <code>ImageItem</code> object,
 * the effect is as if a snapshot is taken of its current contents.  This
 * snapshot is then used for all subsequent painting of the high-level user
 * interface component.  If the application modifies the contents of the
 * image, the application must update the component containing the image (for
 * example, by calling <code>ImageItem.setImage</code>) in order to
 * make the modified
 * contents visible.</p>
 *
 * <p>An immutable image may be created from a mutable image through the
 * use of the {@link #createImage(Image) createImage} method. It is possible
 * to create a mutable copy of an immutable image using a technique similar
 * to the following: </p>
 *
 * <TABLE BORDER="2">
 * <TR>
 * <TD ROWSPAN="1" COLSPAN="1">
 *    <pre><code>
 *    Image source; // the image to be copied    
 *    source = Image.createImage(...);    
 *    Image copy = Image
 *        .createImage(source.getWidth(), source.getHeight());        
 *    Graphics g = copy.getGraphics();    
 *    g.drawImage(source, 0, 0, TOP|LEFT);       </code></pre>
 * </TD>
 * </TR>
 * </TABLE>
 * <a name="alpha"></a>
 * <h3>Alpha Processing</h3>
 *
 * <p>Every pixel within a mutable image is always fully opaque.  Immutable
 * images may contain a combination of fully opaque pixels 
 * <code>(alpha = 2<sup><em>bitdepth</em></sup>&nbsp;-&nbsp;1)</code>, fully
 * transparent pixels (<code>alpha&nbsp;=&nbsp;0</code>), and
 * semitransparent pixels
 * (<code>0&nbsp;&lt;&nbsp;alpha&nbsp;&lt;&nbsp;
 * 2<sup><em>bitdepth</em></sup>&nbsp;-&nbsp;1</code>),
 * where <em>bitdepth</em> is the number of bits per sample in the source data.
 *
 * <p>Implementations must support storage, processing, and rendering of fully
 * opaque pixels and fully transparent pixels in immutable images.  When
 * creating an image from source data (whether from a PNG file or from an
 * array of ARGB data), a fully opaque pixel in the source data must always
 * result in a fully opaque pixel in the new image, and a fully transparent
 * pixel in the source data must always result in a fully transparent pixel in
 * the new image.
 *
 * <p>The required treatment of semitransparent pixel data depends upon
 * whether the implementation supports alpha blending at rendering time.  If
 * the implementation supports alpha blending, a semitransparent pixel in the
 * source data must result in a semitransparent pixel in the new image.  The
 * resulting alpha value may be modified to accommodate the number of levels
 * of semitransparency supported by the platform.  (See the {@link
 * Display#numAlphaLevels() Display.numAlphaLevels()} method.)  If an
 * implementation does not support alpha blending, any semitransparent pixels
 * in the source data must be replaced with fully transparent pixels in the
 * new image.
 *
 * <a name="PNG"></a>
 * <h3>PNG Image Format</h3>
 *
 * <p>Implementations are required to support images stored in the PNG format,
 * as specified by the <em>PNG (Portable Network Graphics) Specification,
 * Version 1.0.</em> All conforming MIDP implementations are also conformant
 * to the minimum set of requirements given by the <em>PNG Specification</em>.
 * MIDP implementations also must conform to additional requirements given
 * here with respect to handling of PNG images.  Note that the requirements
 * listed here take precedence over any conflicting recommendations given in
 * the <em>PNG Specification</em>.</p>
 *
 * <h4>Critical Chunks</h4>
 *
 * <p>All of the 'critical' chunks specified by PNG must be supported. The
 * paragraphs below describe these critical chunks.</p>
 *
 * <p>The IHDR chunk.  MIDP devices must handle the following values in
 * the IHDR chunk:</p>
 *
 * <ul>
 * <li>All positive values of width and height are supported; however, a
 * very large image may not be readable because of memory constraints. The
 * dimensions of the resulting <code>Image</code> object must match 
 * the dimensions of the PNG image.  That is, the values returned by
 * {@link #getWidth() getWidth()} and {@link #getHeight() getHeight()}
 * and the rendered width and height must
 * equal the width and height specified in the IHDR chunk.</li>
 *
 * <li>All color types are supported, although the appearance of the image will
 * be dependent on the capabilities of the device's screen.  Color types that
 * include alpha channel data are supported.</li>
 *
 * <li> For color types <code>4</code> &amp; <code>6</code> (grayscale
 * with alpha and RGB with alpha,
 * respectively) the alpha channel must be decoded. Any pixels with an alpha
 * value of zero must be treated as transparent.  Any pixels with an alpha
 * value of <code>255</code> (for images with <code>8</code> bits per
 * sample) or <code>65535</code> (for images with
 * <code>16</code> bits per sample) must be treated as opaque.  If
 * rendering with alpha
 * blending is supported, any pixels with intermediate alpha values must be
 * carried through to the resulting image.  If alpha blending is not
 * supported, any pixels with intermediate alpha values must be replaced with
 * fully transparent pixels.</li>
 *
 * <li>All bit depth values for the given color type are supported.</li>
 *
 * <li>Compression method <code>0</code> (deflate) is the only
 * supported compression method.
 * This method utilizes the &quot;zlib&quot; compression scheme, which
 * is also used for
 * jar files; thus, the decompression (inflate) code may be shared between the
 * jar decoding and PNG decoding implementations.  As noted in the PNG
 * specification, the compressed data stream may comprised internally of both
 * compressed and uncompressed (raw) data.
 * </li>
 *
 * <li>The filter method represents a series of encoding schemes that may be
 * used to optimize compression.  The PNG spec currently defines a single
 * filter method (method <code>0</code>) that is an adaptive filtering
 * scheme with five
 * basic filter types.  Filtering is essential for optimal compression since it
 * allows the deflate algorithm to exploit spatial similarities within the
 * image.  Therefore, MIDP devices must support all five filter types defined
 * by filter method <code>0</code>.</li>
 *
 * <li> MIDP devices are required to read PNG images that are encoded with
 * either interlace method <code>0</code> (None) or interlace method
 * <code>1</code> (Adam7).  Image
 * loading in MIDP is synchronous and cannot be overlapped with image
 * rendering, and so there is no advantage for an application to use interlace
 * method <code>1</code>.  Support for decoding interlaced images is
 * required for
 * compatibility with PNG and for the convenience of developers who may already
 * have interlaced images available.</li>
 *
 * </ul>
 *
 * <p>The PLTE chunk. Palette-based images must be supported.</p>
 *
 * <p>The IDAT chunk.  Image data may be encoded using any of the
 * <code>5</code> filter
 * types defined by filter method <code>0</code> (None, Sub, Up,
 * Average, Paeth).</p>
 *
 * <p>The IEND chunk.  This chunk must be found in order for the image to be
 * considered valid.</p>
 *
 * <h4>Ancillary Chunks</h4>
 *
 * <p>PNG defines several 'ancillary' chunks that may be present in a
 * PNG image but are not critical for image decoding.</p>
 *
 * <p>The tRNS chunk.  All implementations must support the tRNS chunk.
 * This chunk is used to implement transparency without providing alpha
 * channel data for each pixel. For color types <code>0</code> and
 * <code>2</code>, a particular
 * gray or RGB value is defined to be a transparent pixel.  In this case, the
 * implementation must treat pixels with this value as fully transparent.
 * Pixel value comparison must be based on the actual pixel values using the
 * original sample depth; that is, this comparison must be performed before
 * the pixel values are resampled to reflect the display capabilities
 * of the device. For color type <code>3</code> (indexed color),
 * <code>8</code>-bit alpha values are
 * potentially provided for each entry in the color palette.  In this case,
 * the implementation must treat pixels with an alpha value of
 * <code>0</code> as fully
 * transparent, and it must treat pixels with an alpha value of
 * <code>255</code> as fully
 * opaque.  If rendering with alpha blending is supported, any pixels with
 * intermediate alpha values must be carried through to the resulting image.
 * If alpha blending is not supported, any pixels with intermediate alpha
 * values must be replaced with fully transparent pixels.</p>
 *
 * <p>The implementation <em>may</em> (but is not required to) support
 * any of the other ancillary chunks. The implementation <em>must</em>
 * silently ignore any unsupported ancillary chunks that it encounters.
 * The currently defined optional ancillary chunks are:</p>
 *
 * <PRE>
 *    cHRM gAMA hIST iCCP iTXt pHYs
 *    sBIT sPLT sRGB tEXt tIME zTXt </PRE>
 *
 * <h3>Reference</h3>
 *
 * <p><em>PNG (Portable Network Graphics) Specification, Version 1.0.</em>
 * W3C Recommendation, October 1, 1996. http://www.w3.org/TR/REC-png.html.
 * Also available as RFC 2083, http://www.ietf.org/rfc/rfc2083.txt.</p>
 * @since MIDP 1.0
 */

public class Image {
    /**
     * Construct a new, empty Image
     */
    Image() {}

    /**
     * Creates a new, mutable image for off-screen drawing. Every pixel
     * within the newly created image is white.  The width and height of the
     * image must both be greater than zero.
     *
     * @param width the width of the new image, in pixels
     * @param height the height of the new image, in pixels
     * @return the created image
     *
     * @throws IllegalArgumentException if either <code>width</code> or
     * <code>height</code> is zero or less
     */
    public static Image createImage(int width, int height) {
        if (width <= 0 || height <= 0) {
            throw new IllegalArgumentException();
        }

        // SYNC NOTE: Not accessing any shared data, no locking necessary
        return new MutableImage(width, height);
    }

    /**
     * Creates an immutable image from a source image.
     * If the source image is mutable, an immutable copy is created and
     * returned.  If the source image is immutable, the implementation may
     * simply return it without creating a new image.  If an immutable source
     * image contains transparency information, this information is copied to
     * the new image unchanged.
     *
     * <p> This method is useful for placing the contents of mutable images
     * into <code>Choice</code> objects.  The application can create
     * an off-screen image
     * using the
     * {@link #createImage(int, int) createImage(w, h)}
     * method, draw into it using a <code>Graphics</code> object
     * obtained with the
     * {@link #getGraphics() getGraphics()}
     * method, and then create an immutable copy of it with this method.
     * The immutable copy may then be placed into <code>Choice</code>
     * objects. </p>
     *
     * @param source the source image to be copied
     * @return the new, immutable image
     *
     * @throws NullPointerException if <code>source</code> is <code>null</code>
     */
    public static Image createImage(Image source) {

        // SYNC NOTE: Not accessing any shared data, no locking necessary
        return new ImmutableImage(source);
    }

    /**
     * Creates an immutable image from decoded image data obtained from the
     * named resource.  The name parameter is a resource name as defined by
     * {@link Class#getResourceAsStream(String)
     * Class.getResourceAsStream(name)}.  The rules for resolving resource 
     * names are defined in the
     * <a href="../../../java/lang/package-summary.html">
     * Application Resource Files</a> section of the
     * <code>java.lang</code> package documentation.
     *
     * @param name the name of the resource containing the image data in one of
     * the supported image formats
     * @return the created image
     * @throws NullPointerException if <code>name</code> is <code>null</code>
     * @throws java.io.IOException if the resource does not exist,
     * the data cannot
     * be loaded, or the image data cannot be decoded
     */
    public static Image createImage(java.lang.String name)
	throws java.io.IOException {
        try {
            // SYNC NOTE: Not accessing any shared data, no locking necessary
            return new ImmutableImage(name);
        } catch (IllegalArgumentException e) {
            throw new java.io.IOException();
        }
    }

    /**
     * Creates an immutable image which is decoded from the data stored in
     * the specified byte array at the specified offset and length. The data
     * must be in a self-identifying image file format supported by the
     * implementation, such as <a href="#PNG">PNG</A>.
     *
     * <p>The <code>imageoffset</code> and <code>imagelength</code>
     * parameters specify a range of
     * data within the <code>imageData</code> byte array. The
     * <code>imageOffset</code> parameter
     * specifies the
     * offset into the array of the first data byte to be used. It must
     * therefore lie within the range
     * <code>[0..(imageData.length-1)]</code>. The
     * <code>imageLength</code>
     * parameter specifies the number of data bytes to be used. It must be a
     * positive integer and it must not cause the range to extend beyond
     * the end
     * of the array. That is, it must be true that
     * <code>imageOffset + imageLength &lt; imageData.length</code>. </p>
     *
     * <p> This method is intended for use when loading an
     * image from a variety of sources, such as from
     * persistent storage or from the network.</p>
     *
     * @param imageData the array of image data in a supported image format
     * @param imageOffset the offset of the start of the data in the array
     * @param imageLength the length of the data in the array
     *
     * @return the created image
     * @throws ArrayIndexOutOfBoundsException if <code>imageOffset</code>
     * and <code>imageLength</code>
     * specify an invalid range
     * @throws NullPointerException if <code>imageData</code> is
     * <code>null</code>
     * @throws IllegalArgumentException if <code>imageData</code> is incorrectly
     * formatted or otherwise cannot be decoded
     */
    public static Image createImage(byte[] imageData, int imageOffset,
                                    int imageLength) {

        if (imageOffset < 0 || imageOffset >= imageData.length ||
	    imageLength < 0 ||
	    imageOffset + imageLength > imageData.length) {
            throw new ArrayIndexOutOfBoundsException();