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The Apache PDFBox library is an open source Java tool for working with PDF documents.
There is a newer version: 3.0.2
/*
 * Copyright 2014 The Apache Software Foundation.
 *
 * 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 org.apache.pdfbox.pdmodel.graphics.shading;

import java.awt.Transparency;
import java.awt.color.ColorSpace;
import java.awt.geom.AffineTransform;
import java.awt.image.ColorModel;
import java.awt.image.ComponentColorModel;
import java.awt.image.DataBuffer;
import java.io.IOException;
import org.apache.pdfbox.cos.COSArray;
import org.apache.pdfbox.pdmodel.graphics.color.PDColorSpace;
import org.apache.pdfbox.util.Matrix;

/**
 * A base class to handle what is common to all shading types.
 *
 * @author Shaola Ren
 * @author Tilman Hausherr
 */
public abstract class ShadingContext
{
    private float[] background;
    private int rgbBackground;
    private final PDShading shading;
    private ColorModel outputColorModel;
    private PDColorSpace shadingColorSpace;

    /**
     * Constructor.
     *
     * @param shading the shading type to be used
     * @param cm the color model to be used
     * @param xform transformation for user to device space
     * @param matrix the pattern matrix concatenated with that of the parent content stream
     * @throws java.io.IOException if there is an error getting the color space
     * or doing background color conversion.
     */
    public ShadingContext(PDShading shading, ColorModel cm, AffineTransform xform,
                          Matrix matrix) throws IOException
    {
        this.shading = shading;
        shadingColorSpace = shading.getColorSpace();

        // create the output color model using RGB+alpha as color space
        ColorSpace outputCS = ColorSpace.getInstance(ColorSpace.CS_sRGB);
        outputColorModel = new ComponentColorModel(outputCS, true, false, Transparency.TRANSLUCENT,
                DataBuffer.TYPE_BYTE);

        // get background values if available
        COSArray bg = shading.getBackground();
        if (bg != null)
        {
            background = bg.toFloatArray();
            rgbBackground = convertToRGB(background);
        }
    }

    PDColorSpace getShadingColorSpace()
    {
        return shadingColorSpace;
    }

    PDShading getShading()
    {
        return shading;
    }

    float[] getBackground()
    {
        return background;
    }

    int getRgbBackground()
    {
        return rgbBackground;
    }

    /**
     * Convert color values from shading colorspace to RGB color values encoded
     * into an integer.
     *
     * @param values color values in shading colorspace.
     * @return RGB values encoded in an integer.
     * @throws java.io.IOException if the color conversion fails.
     */
    final int convertToRGB(float[] values) throws IOException
    {
        int normRGBValues;

        float[] rgbValues = shadingColorSpace.toRGB(values);
        normRGBValues = (int) (rgbValues[0] * 255);
        normRGBValues |= (int) (rgbValues[1] * 255) << 8;
        normRGBValues |= (int) (rgbValues[2] * 255) << 16;

        return normRGBValues;
    }
    
    ColorModel getColorModel()
    {
        return outputColorModel;
    }

    void dispose()
    {
        outputColorModel = null;
        shadingColorSpace = null;
    }

}