/*

 * Copyright 2006 Sun Microsystems, Inc.  All Rights Reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Sun designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Sun in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

 * CA 95054 USA or visit www.sun.com if you need additional information or

 * have any questions.

 */

package java.awt;

import java.awt.MultipleGradientPaint.CycleMethod;

import java.awt.MultipleGradientPaint.ColorSpaceType;

import java.awt.geom.AffineTransform;

import java.awt.geom.Rectangle2D;

import java.awt.image.ColorModel;

/**

 * Provides the actual implementation for the RadialGradientPaint.

 * This is where the pixel processing is done.  A RadialGradienPaint

 * only supports circular gradients, but it should be possible to scale

 * the circle to look approximately elliptical, by means of a

 * gradient transform passed into the RadialGradientPaint constructor.

 *

 * @author Nicholas Talian, Vincent Hardy, Jim Graham, Jerry Evans

 */

final class RadialGradientPaintContext extends MultipleGradientPaintContext {

    /** True when (focus == center).  */

    private boolean isSimpleFocus = false;

    /** True when (cycleMethod == NO_CYCLE). */

    private boolean isNonCyclic = false;

    /** Radius of the outermost circle defining the 100% gradient stop. */

    private float radius;

    /** Variables representing center and focus points. */

    private float centerX, centerY, focusX, focusY;

    /** Radius of the gradient circle squared. */

    private float radiusSq;

    /** Constant part of X, Y user space coordinates. */

    private float constA, constB;

    /** Constant second order delta for simple loop. */

    private float gDeltaDelta;

    /**

     * This value represents the solution when focusX == X.  It is called

     * trivial because it is easier to calculate than the general case.

     */

    private float trivial;

    /** Amount for offset when clamping focus. */

    private static final float SCALEBACK = .99f;

    /**

     * Constructor for RadialGradientPaintContext.

     *

     * @param paint the {@code RadialGradientPaint} from which this context

     *              is created

     * @param cm the {@code ColorModel} that receives

     *           the {@code Paint} data (this is used only as a hint)

     * @param deviceBounds the device space bounding box of the

     *                     graphics primitive being rendered

     * @param userBounds the user space bounding box of the

     *                   graphics primitive being rendered

     * @param t the {@code AffineTransform} from user

     *          space into device space (gradientTransform should be

     *          concatenated with this)

     * @param hints the hints that the context object uses to choose

     *              between rendering alternatives

     * @param cx the center X coordinate in user space of the circle defining

     *           the gradient.  The last color of the gradient is mapped to

     *           the perimeter of this circle.

     * @param cy the center Y coordinate in user space of the circle defining

     *           the gradient.  The last color of the gradient is mapped to

     *           the perimeter of this circle.

     * @param r the radius of the circle defining the extents of the

     *          color gradient

     * @param fx the X coordinate in user space to which the first color

     *           is mapped

     * @param fy the Y coordinate in user space to which the first color

     *           is mapped

     * @param fractions the fractions specifying the gradient distribution

     * @param colors the gradient colors

     * @param cycleMethod either NO_CYCLE, REFLECT, or REPEAT

     * @param colorSpace which colorspace to use for interpolation,

     *                   either SRGB or LINEAR_RGB

     */

    RadialGradientPaintContext(RadialGradientPaint paint,

                               ColorModel cm,

                               Rectangle deviceBounds,

                               Rectangle2D userBounds,

                               AffineTransform t,

                               RenderingHints hints,

                               float cx, float cy,

                               float r,

                               float fx, float fy,

                               float[] fractions,

                               Color[] colors,

                               CycleMethod cycleMethod,

                               ColorSpaceType colorSpace)

    {

        super(paint, cm, deviceBounds, userBounds, t, hints,

              fractions, colors, cycleMethod, colorSpace);

        // copy some parameters

        centerX = cx;

        centerY = cy;

        focusX = fx;

        focusY = fy;

        radius = r;

        this.isSimpleFocus = (focusX == centerX) && (focusY == centerY);

        this.isNonCyclic = (cycleMethod == CycleMethod.NO_CYCLE);

        // for use in the quadractic equation

        radiusSq = radius * radius;

        float dX = focusX - centerX;

        float dY = focusY - centerY;

        double distSq = (dX * dX) + (dY * dY);

        // test if distance from focus to center is greater than the radius

        if (distSq > radiusSq * SCALEBACK) {

            // clamp focus to radius

            float scalefactor = (float)Math.sqrt(radiusSq * SCALEBACK / distSq);

            dX = dX * scalefactor;

            dY = dY * scalefactor;

            focusX = centerX + dX;

            focusY = centerY + dY;

        }

        // calculate the solution to be used in the case where X == focusX

        // in cyclicCircularGradientFillRaster()

        trivial = (float)Math.sqrt(radiusSq - (dX * dX));

        // constant parts of X, Y user space coordinates

        constA = a02 - centerX;

        constB = a12 - centerY;

        // constant second order delta for simple loop

        gDeltaDelta = 2 * ( a00 *  a00 +  a10 *  a10) / radiusSq;

    }

    /**

     * Return a Raster containing the colors generated for the graphics

     * operation.

     *

     * @param x,y,w,h the area in device space for which colors are

     * generated.

     */

    protected void fillRaster(int pixels[], int off, int adjust,

                              int x, int y, int w, int h)

    {

        if (isSimpleFocus && isNonCyclic && isSimpleLookup) {

            simpleNonCyclicFillRaster(pixels, off, adjust, x, y, w, h);

        } else {

            cyclicCircularGradientFillRaster(pixels, off, adjust, x, y, w, h);

        }

    }

    /**

     * This code works in the simplest of cases, where the focus == center

     * point, the gradient is noncyclic, and the gradient lookup method is

     * fast (single array index, no conversion necessary).

     */

    private void simpleNonCyclicFillRaster(int pixels[], int off, int adjust,

                                           int x, int y, int w, int h)

    {

        /* We calculate sqrt(X^2 + Y^2) relative to the radius

         * size to get the fraction for the color to use.

         *

         * Each step along the scanline adds (a00, a10) to (X, Y).

         * If we precalculate:

         *   gRel = X^2+Y^2

         * for the start of the row, then for each step we need to

         * calculate:

         *   gRel' = (X+a00)^2 + (Y+a10)^2

         *         = X^2 + 2*X*a00 + a00^2 + Y^2 + 2*Y*a10 + a10^2

         *         = (X^2+Y^2) + 2*(X*a00+Y*a10) + (a00^2+a10^2)

         *         = gRel + 2*(X*a00+Y*a10) + (a00^2+a10^2)

         *         = gRel + 2*DP + SD

         * (where DP = dot product between X,Y and a00,a10

         *  and   SD = dot product square of the delta vector)

         * For the step after that we get:

         *   gRel'' = (X+2*a00)^2 + (Y+2*a10)^2

         *          = X^2 + 4*X*a00 + 4*a00^2 + Y^2 + 4*Y*a10 + 4*a10^2

         *          = (X^2+Y^2) + 4*(X*a00+Y*a10) + 4*(a00^2+a10^2)

         *          = gRel  + 4*DP + 4*SD

         *          = gRel' + 2*DP + 3*SD

         * The increment changed by:

         *     (gRel'' - gRel') - (gRel' - gRel)

         *   = (2*DP + 3*SD) - (2*DP + SD)

         *   = 2*SD

         * Note that this value depends only on the (inverse of the)

         * transformation matrix and so is a constant for the loop.

         * To make this all relative to the unit circle, we need to

         * divide all values as follows:

         *   [XY] /= radius

         *   gRel /= radiusSq

         *   DP   /= radiusSq

         *   SD   /= radiusSq

         */

        // coordinates of UL corner in "user space" relative to center

        float rowX = (a00*x) + (a01*y) + constA;

        float rowY = (a10*x) + (a11*y) + constB;

        // second order delta calculated in constructor

        float gDeltaDelta = this.gDeltaDelta;

        // adjust is (scan-w) of pixels array, we need (scan)

        adjust += w;

        // rgb of the 1.0 color used when the distance exceeds gradient radius

        int rgbclip = gradient[fastGradientArraySize];

        for (int j = 0; j < h; j++) {

            // these values depend on the coordinates of the start of the row

            float gRel   =      (rowX * rowX + rowY * rowY) / radiusSq;

            float gDelta = (2 * ( a00 * rowX +  a10 * rowY) / radiusSq +

                            gDeltaDelta/2);

            /* Use optimized loops for any cases where gRel >= 1.

             * We do not need to calculate sqrt(gRel) for these

             * values since sqrt(N>=1) == (M>=1).

             * Note that gRel follows a parabola which can only be < 1

             * for a small region around the center on each scanline. In

             * particular:

             *   gDeltaDelta is always positive

             *   gDelta is <0 until it crosses the midpoint, then >0

             * To the left and right of that region, it will always be

             * >=1 out to infinity, so we can process the line in 3

             * regions:

             *   out to the left  - quick fill until gRel < 1, updating gRel

             *   in the heart     - slow fraction=sqrt fill while gRel < 1

             *   out to the right - quick fill rest of scanline, ignore gRel

             */

            int i = 0;

            // Quick fill for "out to the left"

            while (i < w && gRel >= 1.0f) {

                pixels[off + i] = rgbclip;

                gRel += gDelta;

                gDelta += gDeltaDelta;

                i++;

            }

            // Slow fill for "in the heart"

            while (i < w && gRel < 1.0f) {

                int gIndex;

                if (gRel <= 0) {

                    gIndex = 0;

                } else {

                    float fIndex = gRel * SQRT_LUT_SIZE;

                    int iIndex = (int) (fIndex);

                    float s0 = sqrtLut[iIndex];

                    float s1 = sqrtLut[iIndex+1] - s0;

                    fIndex = s0 + (fIndex - iIndex) * s1;

                    gIndex = (int) (fIndex * fastGradientArraySize);

                }

                // store the color at this point

                pixels[off + i] = gradient[gIndex];

                // incremental calculation

                gRel += gDelta;

                gDelta += gDeltaDelta;

                i++;

            }

            // Quick fill to end of line for "out to the right"

            while (i < w) {

                pixels[off + i] = rgbclip;

                i++;

            }

            off += adjust;

            rowX += a01;

            rowY += a11;

        }

    }

    // SQRT_LUT_SIZE must be a power of 2 for the test above to work.

    private static final int SQRT_LUT_SIZE = (1 << 11);

    private static float sqrtLut[] = new float[SQRT_LUT_SIZE+1];

    static {

        for (int i = 0; i < sqrtLut.length; i++) {

            sqrtLut[i] = (float) Math.sqrt(i / ((float) SQRT_LUT_SIZE));

        }

    }

    /**

     * Fill the raster, cycling the gradient colors when a point falls outside

     * of the perimeter of the 100% stop circle.

     *

     * This calculation first computes the intersection point of the line

     * from the focus through the current point in the raster, and the

     * perimeter of the gradient circle.

     *

     * Then it determines the percentage distance of the current point along

     * that line (focus is 0%, perimeter is 100%).

     *

     * Equation of a circle centered at (a,b) with radius r:

     *     (x-a)^2 + (y-b)^2 = r^2

     * Equation of a line with slope m and y-intercept b:

     *     y = mx + b

     * Replacing y in the circle equation and solving using the quadratic

     * formula produces the following set of equations.  Constant factors have

     * been extracted out of the inner loop.

     */

    private void cyclicCircularGradientFillRaster(int pixels[], int off,

                                                  int adjust,

                                                  int x, int y,

                                                  int w, int h)

    {

        // constant part of the C factor of the quadratic equation

        final double constC =

            -radiusSq + (centerX * centerX) + (centerY * centerY);

        // coefficients of the quadratic equation (Ax^2 + Bx + C = 0)

        double A, B, C;

        // slope and y-intercept of the focus-perimeter line

        double slope, yintcpt;

        // intersection with circle X,Y coordinate

        double solutionX, solutionY;

        // constant parts of X, Y coordinates

        final float constX = (a00*x) + (a01*y) + a02;

        final float constY = (a10*x) + (a11*y) + a12;

        // constants in inner loop quadratic formula

        final float precalc2 =  2 * centerY;

        final float precalc3 = -2 * centerX;

        // value between 0 and 1 specifying position in the gradient

        float g;

        // determinant of quadratic formula (should always be > 0)

        float det;

        // sq distance from the current point to focus

        float currentToFocusSq;

        // sq distance from the intersect point to focus

        float intersectToFocusSq;

        // temp variables for change in X,Y squared

        float deltaXSq, deltaYSq;

        // used to index pixels array

        int indexer = off;

        // incremental index change for pixels array

        int pixInc = w+adjust;

        // for every row

        for (int j = 0; j < h; j++) {

            // user space point; these are constant from column to column

            float X = (a01*j) + constX;

            float Y = (a11*j) + constY;

            // for every column (inner loop begins here)

            for (int i = 0; i < w; i++) {

                if (X == focusX) {

                    // special case to avoid divide by zero

                    solutionX = focusX;

                    solutionY = centerY;

                    solutionY += (Y > focusY) ? trivial : -trivial;

                } else {

                    // slope and y-intercept of the focus-perimeter line

                    slope = (Y - focusY) / (X - focusX);

                    yintcpt = Y - (slope * X);

                    // use the quadratic formula to calculate the

                    // intersection point

                    A = (slope * slope) + 1;

                    B = precalc3 + (-2 * slope * (centerY - yintcpt));

                    C = constC + (yintcpt* (yintcpt - precalc2));

                    det = (float)Math.sqrt((B * B) - (4 * A * C));

                    solutionX = -B;

                    // choose the positive or negative root depending

                    // on where the X coord lies with respect to the focus

                    solutionX += (X < focusX)? -det : det;

                    solutionX = solutionX / (2 * A); // divisor

                    solutionY = (slope * solutionX) + yintcpt;

                }

                // Calculate the square of the distance from the current point

                // to the focus and the square of the distance from the

                // intersection point to the focus. Want the squares so we can

                // do 1 square root after division instead of 2 before.

                deltaXSq = X - focusX;

                deltaXSq = deltaXSq * deltaXSq;

                deltaYSq = Y - focusY;

                deltaYSq = deltaYSq * deltaYSq;

                currentToFocusSq = deltaXSq + deltaYSq;

                deltaXSq = (float)solutionX - focusX;

                deltaXSq = deltaXSq * deltaXSq;

                deltaYSq = (float)solutionY - focusY;

                deltaYSq = deltaYSq * deltaYSq;

                intersectToFocusSq = deltaXSq + deltaYSq;

                // get the percentage (0-1) of the current point along the

                // focus-circumference line

                g = (float)Math.sqrt(currentToFocusSq / intersectToFocusSq);

                // store the color at this point

                pixels[indexer + i] = indexIntoGradientsArrays(g);

                // incremental change in X, Y

                X += a00;

                Y += a10;

            } //end inner loop

            indexer += pixInc;

        } //end outer loop

    }

}