Android Open Source - esr-scanner Luminance Source

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Apache License

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/*
 * Copyright 2009 ZXing authors//from  w w w  .j  ava 2  s  .com
 * Copyright 2011 Robert Theis
 *
 * 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 ch.luklanis.esscan;

/**
 * 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.
 * <p/>
 * The code for this class was adapted from the ZXing project: http://code.google.com/p/zxing
 */
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, 0 <= y < 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:
     * 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 true;
    }

    /**
     * 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, 0 <= left < getWidth().
     * @param top    The top coordinate, 0 <= top <= 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 RuntimeException("This luminance source does not support cropping.");
    }

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

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

}

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