# AxialShadingContext.java

    /*
     * Licensed to the Apache Software Foundation (ASF) under one or more
     * contributor license agreements.  See the NOTICE file distributed with
     * this work for additional information regarding copyright ownership.
     * The ASF licenses this file to You 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.Rectangle;
    import java.awt.geom.AffineTransform;
    import java.awt.geom.NoninvertibleTransformException;
    import java.awt.image.ColorModel;
    import java.awt.image.Raster;
    import java.awt.image.WritableRaster;
    import java.io.IOException;
    import org.apache.commons.logging.Log;
    import org.apache.commons.logging.LogFactory;
    import org.apache.pdfbox.cos.COSArray;
    import org.apache.pdfbox.cos.COSBoolean;
    import org.apache.pdfbox.pdmodel.common.function.PDFunction;
    import org.apache.pdfbox.util.Matrix;

    /**
     * AWT PaintContext for axial shading.
     *
     * Performance improvement done as part of GSoC2014, Tilman Hausherr is the mentor.
     *
     * @author Shaola Ren
     */
    public class AxialShadingContext extends ShadingContext
    {
        private static final Log LOG = LogFactory.getLog(AxialShadingContext.class);

        private PDShadingType2 axialShadingType;

        private final float[] coords;
        private final float[] domain;
        private final boolean[] extend;
        private final double x1x0;
        private final double y1y0;
        private final float d1d0;
        private final double denom;

        private final int factor;
        private final int[] colorTable;

        private AffineTransform rat;

        /**
         * Constructor creates an instance to be used for fill operations.
         *
         * @param shading the shading type to be used
         * @param colorModel 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
         * @param deviceBounds the bounds of the area to paint, in device units
         * @throws IOException if there is an error getting the color space or doing color conversion.
         */
        public AxialShadingContext(PDShadingType2 shading, ColorModel colorModel, AffineTransform xform,
                                   Matrix matrix, Rectangle deviceBounds) throws IOException
        {
            super(shading, colorModel, xform, matrix);
            this.axialShadingType = shading;
            coords = shading.getCoords().toFloatArray();

            // domain values
            if (shading.getDomain() != null)
            {
                domain = shading.getDomain().toFloatArray();
            }
            else
            {
                // set default values
                domain = new float[] { 0, 1 };
            }
            // extend values
            COSArray extendValues = shading.getExtend();
            if (extendValues != null)
            {
                extend = new boolean[2];
                extend[0] = ((COSBoolean) extendValues.getObject(0)).getValue();
                extend[1] = ((COSBoolean) extendValues.getObject(1)).getValue();
            }
            else
            {
                // set default values
                extend = new boolean[] { false, false };
            }
            // calculate some constants to be used in getRaster
            x1x0 = coords[2] - coords[0];
            y1y0 = coords[3] - coords[1];
            d1d0 = domain[1] - domain[0];
            denom = Math.pow(x1x0, 2) + Math.pow(y1y0, 2);

            try
            {
                // get inverse transform to be independent of current user / device space
                // when handling actual pixels in getRaster()
                rat = matrix.createAffineTransform().createInverse();
                rat.concatenate(xform.createInverse());
            }
            catch (NoninvertibleTransformException ex)
            {
                LOG.error(ex.getMessage() + ", matrix: " + matrix, ex);
                rat = new AffineTransform();
            }

            // shading space -> device space
            AffineTransform shadingToDevice = (AffineTransform)xform.clone();
            shadingToDevice.concatenate(matrix.createAffineTransform());

            // worst case for the number of steps is opposite diagonal corners, so use that
            double dist = Math.sqrt(Math.pow(deviceBounds.getMaxX() - deviceBounds.getMinX(), 2) +
                                    Math.pow(deviceBounds.getMaxY() - deviceBounds.getMinY(), 2));
            factor = (int) Math.ceil(dist);

            // build the color table for the given number of steps
            colorTable = calcColorTable();
        }

        /**
         * Calculate the color on the axial line and store them in an array.
         *
         * @return an array, index denotes the relative position, the corresponding
         * value is the color on the axial line
         * @throws IOException if the color conversion fails.
         */
        private int[] calcColorTable() throws IOException
        {
            int[] map = new int[factor + 1];
            if (factor == 0 || Float.compare(d1d0, 0) == 0)
            {
                float[] values = axialShadingType.evalFunction(domain[0]);
                map[0] = convertToRGB(values);
            }
            else
            {
                for (int i = 0; i <= factor; i++)
                {
                    float t = domain[0] + d1d0 * i / factor;
                    float[] values = axialShadingType.evalFunction(t);
                    map[i] = convertToRGB(values);
                }
            }
            return map;
        }

        @Override
        public void dispose()
        {
            super.dispose();
            axialShadingType = null;
        }

        @Override
        public Raster getRaster(int x, int y, int w, int h)
        {
            // create writable raster
            WritableRaster raster = getColorModel().createCompatibleWritableRaster(w, h);
            boolean useBackground;
            int[] data = new int[w * h * 4];
            float[] values = new float[2];
            for (int j = 0; j < h; j++)
            {
                for (int i = 0; i < w; i++)
                {
                    useBackground = false;
                    values[0] = x + i;
                    values[1] = y + j;
                    rat.transform(values, 0, values, 0, 1);
                    double inputValue = x1x0 * (values[0] - coords[0]) + y1y0 * (values[1] - coords[1]);
                    // TODO this happens if start == end, see PDFBOX-1442
                    if (Double.compare(denom, 0) == 0)
                    {
                        if (getBackground() == null)
                        {
                            continue;
                        }
                        useBackground = true;
                    }
                    else
                    {
                        inputValue /= denom;
                    }
                    // input value is out of range
                    if (inputValue < 0)
                    {
                        // the shading has to be extended if extend[0] == true
                        if (extend[0])
                        {
                            inputValue = domain[0];
                        }
                        else
                        {
                            if (getBackground() == null)
                            {
                                continue;
                            }
                            useBackground = true;
                        }
                    }
                    // input value is out of range
                    else if (inputValue > 1)
                    {
                        // the shading has to be extended if extend[1] == true
                        if (extend[1])
                        {
                            inputValue = domain[1];
                        }
                        else
                        {
                            if (getBackground() == null)
                            {
                                continue;
                            }
                            useBackground = true;
                        }
                    }
                    int value;
                    if (useBackground)
                    {
                        // use the given background color values
                        value = getRgbBackground();
                    }
                    else
                    {
                        int key = (int) (inputValue * factor);
                        value = colorTable[key];
                    }
                    int index = (j * w + i) * 4;
                    data[index] = value & 255;
                    value >>= 8;
                    data[index + 1] = value & 255;
                    value >>= 8;
                    data[index + 2] = value & 255;
                    data[index + 3] = 255;
                }
            }
            raster.setPixels(0, 0, w, h, data);
            return raster;
        }

        /**
         * Returns the coords values.
         */
        public float[] getCoords()
        {
            return coords;
        }

        /**
         * Returns the domain values.
         */
        public float[] getDomain()
        {
            return domain;
        }

        /**
         * Returns the extend values.
         */
        public boolean[] getExtend()
        {
            return extend;
        }

        /**
         * Returns the function.
         *
         * @throws java.io.IOException if we were not able to create the function.
         */
        public PDFunction getFunction() throws IOException
        {
            return axialShadingType.getFunction();
        }
    }