LuminanceSource.java

/*
 * Copyright 2009 ZXing authors
 *
 * 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.zxing;

/**
 * The purpose of this class hierarchy is to abstract different bitmap
 * implementations across platforms into a standard interface for requesting
 * greyscale luminance values. The interface only provides immutable methods;
 * therefore crop and rotation create copies. This is to ensure that one Reader
 * does not modify the original luminance source and leave it in an unknown
 * state for other Readers in the chain.
 * 
 * @author dswitkin@google.com (Daniel Switkin)
 */
public abstract class LuminanceSource {

	private final int width;
	private final int height;

	protected LuminanceSource(int width, int height) {
		this.width = width;
		this.height = height;
	}

	/**
	 * Fetches one row of luminance data from the underlying platform's bitmap.
	 * Values range from 0 (black) to 255 (white). Because Java does not have an
	 * unsigned byte type, callers will have to bitwise and with 0xff for each
	 * value. It is preferable for implementations of this method to only fetch
	 * this row rather than the whole image, since no 2D Readers may be
	 * installed and getMatrix() may never be called.
	 * 
	 * @param y
	 *            The row to fetch, which must be in [0,getHeight())
	 * @param row
	 *            An optional preallocated array. If null or too small, it will
	 *            be ignored. Always use the returned object, and ignore the
	 *            .length of the array.
	 * @return An array containing the luminance data.
	 */
	public abstract byte[] getRow(int y, byte[] row);

	/**
	 * Fetches luminance data for the underlying bitmap. Values should be
	 * fetched using: {@code int luminance = array[y * width + x] & 0xff}
	 * 
	 * @return A row-major 2D array of luminance values. Do not use
	 *         result.length as it may be larger than width * height bytes on
	 *         some platforms. Do not modify the contents of the result.
	 */
	public abstract byte[] getMatrix();

	/**
	 * @return The width of the bitmap.
	 */
	public final int getWidth() {
		return width;
	}

	/**
	 * @return The height of the bitmap.
	 */
	public final int getHeight() {
		return height;
	}

	/**
	 * @return Whether this subclass supports cropping.
	 */
	public boolean isCropSupported() {
		return false;
	}

	/**
	 * Returns a new object with cropped image data. Implementations may keep a
	 * reference to the original data rather than a copy. Only callable if
	 * isCropSupported() is true.
	 * 
	 * @param left
	 *            The left coordinate, which must be in [0,getWidth())
	 * @param top
	 *            The top coordinate, which must be in [0,getHeight())
	 * @param width
	 *            The width of the rectangle to crop.
	 * @param height
	 *            The height of the rectangle to crop.
	 * @return A cropped version of this object.
	 */
	public LuminanceSource crop(int left, int top, int width, int height) {
		throw new UnsupportedOperationException(
				"This luminance source does not support cropping.");
	}

	/**
	 * @return Whether this subclass supports counter-clockwise rotation.
	 */
	public boolean isRotateSupported() {
		return false;
	}

	/**
	 * @return a wrapper of this {@code LuminanceSource} which inverts the
	 *         luminances it returns -- black becomes white and vice versa, and
	 *         each value becomes (255-value).
	 */
	public LuminanceSource invert() {
		return new InvertedLuminanceSource(this);
	}

	/**
	 * Returns a new object with rotated image data by 90 degrees
	 * counterclockwise. Only callable if {@link #isRotateSupported()} is true.
	 * 
	 * @return A rotated version of this object.
	 */
	public LuminanceSource rotateCounterClockwise() {
		throw new UnsupportedOperationException(
				"This luminance source does not support rotation by 90 degrees.");
	}

	/**
	 * Returns a new object with rotated image data by 45 degrees
	 * counterclockwise. Only callable if {@link #isRotateSupported()} is true.
	 * 
	 * @return A rotated version of this object.
	 */
	public LuminanceSource rotateCounterClockwise45() {
		throw new UnsupportedOperationException(
				"This luminance source does not support rotation by 45 degrees.");
	}

	@Override
	public final String toString() {
		byte[] row = new byte[width];
		StringBuilder result = new StringBuilder(height * (width + 1));
		for (int y = 0; y < height; y++) {
			row = getRow(y, row);
			for (int x = 0; x < width; x++) {
				int luminance = row[x] & 0xFF;
				char c;
				if (luminance < 0x40) {
					c = '#';
				} else if (luminance < 0x80) {
					c = '+';
				} else if (luminance < 0xC0) {
					c = '.';
				} else {
					c = ' ';
				}
				result.append(c);
			}
			result.append('\n');
		}
		return result.toString();
	}

}