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package java.awt;

import java.awt.geom.AffineTransform;
import java.awt.geom.Point2D;
import java.awt.geom.Rectangle2D;
import java.awt.image.ColorModel;
import java.beans.ConstructorProperties;


The LinearGradientPaint class provides a way to fill a Shape with a linear color gradient pattern. The user may specify two or more gradient colors, and this paint will provide an interpolation between each color. The user also specifies start and end points which define where in user space the color gradient should begin and end. 

The user must provide an array of floats specifying how to distribute the
colors along the gradient.  These values should range from 0.0 to 1.0 and
act like keyframes along the gradient (they mark where the gradient should
be exactly a particular color).


In the event that the user does not set the first keyframe value equal
to 0 and/or the last keyframe value equal to 1, keyframes will be created
at these positions and the first and last colors will be replicated there.
So, if a user specifies the following arrays to construct a gradient:


    {Color.BLUE, Color.RED}, {.3f, .7f}


this will be converted to a gradient with the following keyframes:


    {Color.BLUE, Color.BLUE, Color.RED, Color.RED}, {0f, .3f, .7f, 1f}



 The user may also select what action the LinearGradientPaint object takes when it is filling the space outside the start and end points by setting CycleMethod to either REFLECTION or REPEAT. The distances between any two colors in any of the reflected or repeated copies of the gradient are the same as the distance between those same two colors between the start and end points. Note that some minor variations in distances may occur due to sampling at the granularity of a pixel. If no cycle method is specified, NO_CYCLE will be chosen by default, which means the endpoint colors will be used to fill the remaining area. 

The colorSpace parameter allows the user to specify in which colorspace
the interpolation should be performed, default sRGB or linearized RGB.

 The following code demonstrates typical usage of LinearGradientPaint: 
    Point2D start = new Point2D.Float(0, 0);
    Point2D end = new Point2D.Float(50, 50);
    float[] dist = {0.0f, 0.2f, 1.0f};
    Color[] colors = {Color.RED, Color.WHITE, Color.BLUE};
    LinearGradientPaint p =
        new LinearGradientPaint(start, end, dist, colors);



 This code will create a LinearGradientPaint which interpolates between red and white for the first 20% of the gradient and between white and blue for the remaining 80%. 

This image demonstrates the example code above for each
of the three cycle methods:






Author:Nicholas Talian, Vincent Hardy, Jim Graham, Jerry Evans
See Also:
Since:1.6
/**
 * The {@code LinearGradientPaint} class provides a way to fill
 * a {@link java.awt.Shape} with a linear color gradient pattern.  The user
 * may specify two or more gradient colors, and this paint will provide an
 * interpolation between each color.  The user also specifies start and end
 * points which define where in user space the color gradient should begin
 * and end.
 * <p>
 * The user must provide an array of floats specifying how to distribute the
 * colors along the gradient.  These values should range from 0.0 to 1.0 and
 * act like keyframes along the gradient (they mark where the gradient should
 * be exactly a particular color).
 * <p>
 * In the event that the user does not set the first keyframe value equal
 * to 0 and/or the last keyframe value equal to 1, keyframes will be created
 * at these positions and the first and last colors will be replicated there.
 * So, if a user specifies the following arrays to construct a gradient:<br>
 * <pre>
 *     {Color.BLUE, Color.RED}, {.3f, .7f}
 * </pre>
 * this will be converted to a gradient with the following keyframes:<br>
 * <pre>
 *     {Color.BLUE, Color.BLUE, Color.RED, Color.RED}, {0f, .3f, .7f, 1f}
 * </pre>
 *
 * <p>
 * The user may also select what action the {@code LinearGradientPaint} object
 * takes when it is filling the space outside the start and end points by
 * setting {@code CycleMethod} to either {@code REFLECTION} or {@code REPEAT}.
 * The distances between any two colors in any of the reflected or repeated
 * copies of the gradient are the same as the distance between those same two
 * colors between the start and end points.
 * Note that some minor variations in distances may occur due to sampling at
 * the granularity of a pixel.
 * If no cycle method is specified, {@code NO_CYCLE} will be chosen by
 * default, which means the endpoint colors will be used to fill the
 * remaining area.
 * <p>
 * The colorSpace parameter allows the user to specify in which colorspace
 * the interpolation should be performed, default sRGB or linearized RGB.
 *
 * <p>
 * The following code demonstrates typical usage of
 * {@code LinearGradientPaint}:
 * <pre>
 *     Point2D start = new Point2D.Float(0, 0);
 *     Point2D end = new Point2D.Float(50, 50);
 *     float[] dist = {0.0f, 0.2f, 1.0f};
 *     Color[] colors = {Color.RED, Color.WHITE, Color.BLUE};
 *     LinearGradientPaint p =
 *         new LinearGradientPaint(start, end, dist, colors);
 * </pre>
 * <p>
 * This code will create a {@code LinearGradientPaint} which interpolates
 * between red and white for the first 20% of the gradient and between white
 * and blue for the remaining 80%.
 *
 * <p>
 * This image demonstrates the example code above for each
 * of the three cycle methods:
 * <center>
 * <img src = "doc-files/LinearGradientPaint.png"
 * alt="image showing the output of the example code">
 * </center>
 *
 * @see java.awt.Paint
 * @see java.awt.Graphics2D#setPaint
 * @author Nicholas Talian, Vincent Hardy, Jim Graham, Jerry Evans
 * @since 1.6
 */
public final class LinearGradientPaint extends MultipleGradientPaint {

    
Gradient start and end points. 
/** Gradient start and end points. */
    private final Point2D start, end;

    
Constructs a LinearGradientPaint with a default NO_CYCLE repeating method and SRGB color space. 
Params:
  • startX – the X coordinate of the gradient axis start point
              in user space
  • startY – the Y coordinate of the gradient axis start point
              in user space
  • endX –   the X coordinate of the gradient axis end point
              in user space
  • endY –   the Y coordinate of the gradient axis end point
              in user space
  • fractions – numbers ranging from 0.0 to 1.0 specifying the
                 distribution of colors along the gradient
  • colors – array of colors corresponding to each fractional value
Throws:
  • NullPointerException –  if fractions array is null, or colors array is null,
  • IllegalArgumentException –  if start and end points are the same points, or fractions.length != colors.length, or colors is less than 2 in size, or a fractions value is less than 0.0 or greater than 1.0, or the fractions are not provided in strictly increasing order
/**
     * Constructs a {@code LinearGradientPaint} with a default
     * {@code NO_CYCLE} repeating method and {@code SRGB} color space.
     *
     * @param startX the X coordinate of the gradient axis start point
     *               in user space
     * @param startY the Y coordinate of the gradient axis start point
     *               in user space
     * @param endX   the X coordinate of the gradient axis end point
     *               in user space
     * @param endY   the Y coordinate of the gradient axis end point
     *               in user space
     * @param fractions numbers ranging from 0.0 to 1.0 specifying the
     *                  distribution of colors along the gradient
     * @param colors array of colors corresponding to each fractional value
     *
     * @throws NullPointerException
     * if {@code fractions} array is null,
     * or {@code colors} array is null,
     * @throws IllegalArgumentException
     * if start and end points are the same points,
     * or {@code fractions.length != colors.length},
     * or {@code colors} is less than 2 in size,
     * or a {@code fractions} value is less than 0.0 or greater than 1.0,
     * or the {@code fractions} are not provided in strictly increasing order
     */
    public LinearGradientPaint(float startX, float startY,
                               float endX, float endY,
                               float[] fractions, Color[] colors)
    {
        this(new Point2D.Float(startX, startY),
             new Point2D.Float(endX, endY),
             fractions,
             colors,
             CycleMethod.NO_CYCLE);
    }

    
Constructs a LinearGradientPaint with a default SRGB color space. 
Params:
  • startX – the X coordinate of the gradient axis start point
              in user space
  • startY – the Y coordinate of the gradient axis start point
              in user space
  • endX –   the X coordinate of the gradient axis end point
              in user space
  • endY –   the Y coordinate of the gradient axis end point
              in user space
  • fractions – numbers ranging from 0.0 to 1.0 specifying the
                 distribution of colors along the gradient
  • colors – array of colors corresponding to each fractional value
  • cycleMethod – either NO_CYCLE, REFLECT, or REPEAT
Throws:
  • NullPointerException –  if fractions array is null, or colors array is null, or cycleMethod is null
  • IllegalArgumentException –  if start and end points are the same points, or fractions.length != colors.length, or colors is less than 2 in size, or a fractions value is less than 0.0 or greater than 1.0, or the fractions are not provided in strictly increasing order
/**
     * Constructs a {@code LinearGradientPaint} with a default {@code SRGB}
     * color space.
     *
     * @param startX the X coordinate of the gradient axis start point
     *               in user space
     * @param startY the Y coordinate of the gradient axis start point
     *               in user space
     * @param endX   the X coordinate of the gradient axis end point
     *               in user space
     * @param endY   the Y coordinate of the gradient axis end point
     *               in user space
     * @param fractions numbers ranging from 0.0 to 1.0 specifying the
     *                  distribution of colors along the gradient
     * @param colors array of colors corresponding to each fractional value
     * @param cycleMethod either {@code NO_CYCLE}, {@code REFLECT},
     *                    or {@code REPEAT}
     *
     * @throws NullPointerException
     * if {@code fractions} array is null,
     * or {@code colors} array is null,
     * or {@code cycleMethod} is null
     * @throws IllegalArgumentException
     * if start and end points are the same points,
     * or {@code fractions.length != colors.length},
     * or {@code colors} is less than 2 in size,
     * or a {@code fractions} value is less than 0.0 or greater than 1.0,
     * or the {@code fractions} are not provided in strictly increasing order
     */
    public LinearGradientPaint(float startX, float startY,
                               float endX, float endY,
                               float[] fractions, Color[] colors,
                               CycleMethod cycleMethod)
    {
        this(new Point2D.Float(startX, startY),
             new Point2D.Float(endX, endY),
             fractions,
             colors,
             cycleMethod);
    }

    
Constructs a LinearGradientPaint with a default NO_CYCLE repeating method and SRGB color space. 
Params:
  • start – the gradient axis start Point2D in user space
  • end – the gradient axis end Point2D in user space
  • fractions – numbers ranging from 0.0 to 1.0 specifying the
                 distribution of colors along the gradient
  • colors – array of colors corresponding to each fractional value
Throws:
  • NullPointerException –  if one of the points is null, or fractions array is null, or colors array is null
  • IllegalArgumentException –  if start and end points are the same points, or fractions.length != colors.length, or colors is less than 2 in size, or a fractions value is less than 0.0 or greater than 1.0, or the fractions are not provided in strictly increasing order
/**
     * Constructs a {@code LinearGradientPaint} with a default
     * {@code NO_CYCLE} repeating method and {@code SRGB} color space.
     *
     * @param start the gradient axis start {@code Point2D} in user space
     * @param end the gradient axis end {@code Point2D} in user space
     * @param fractions numbers ranging from 0.0 to 1.0 specifying the
     *                  distribution of colors along the gradient
     * @param colors array of colors corresponding to each fractional value
     *
     * @throws NullPointerException
     * if one of the points is null,
     * or {@code fractions} array is null,
     * or {@code colors} array is null
     * @throws IllegalArgumentException
     * if start and end points are the same points,
     * or {@code fractions.length != colors.length},
     * or {@code colors} is less than 2 in size,
     * or a {@code fractions} value is less than 0.0 or greater than 1.0,
     * or the {@code fractions} are not provided in strictly increasing order
     */
    public LinearGradientPaint(Point2D start, Point2D end,
                               float[] fractions, Color[] colors)
    {
        this(start, end,
             fractions, colors,
             CycleMethod.NO_CYCLE);
    }

    
Constructs a LinearGradientPaint with a default SRGB color space. 
Params:
  • start – the gradient axis start Point2D in user space
  • end – the gradient axis end Point2D in user space
  • fractions – numbers ranging from 0.0 to 1.0 specifying the
                 distribution of colors along the gradient
  • colors – array of colors corresponding to each fractional value
  • cycleMethod – either NO_CYCLE, REFLECT, or REPEAT
Throws:
  • NullPointerException –  if one of the points is null, or fractions array is null, or colors array is null, or cycleMethod is null
  • IllegalArgumentException –  if start and end points are the same points, or fractions.length != colors.length, or colors is less than 2 in size, or a fractions value is less than 0.0 or greater than 1.0, or the fractions are not provided in strictly increasing order
/**
     * Constructs a {@code LinearGradientPaint} with a default {@code SRGB}
     * color space.
     *
     * @param start the gradient axis start {@code Point2D} in user space
     * @param end the gradient axis end {@code Point2D} in user space
     * @param fractions numbers ranging from 0.0 to 1.0 specifying the
     *                  distribution of colors along the gradient
     * @param colors array of colors corresponding to each fractional value
     * @param cycleMethod either {@code NO_CYCLE}, {@code REFLECT},
     *                    or {@code REPEAT}
     *
     * @throws NullPointerException
     * if one of the points is null,
     * or {@code fractions} array is null,
     * or {@code colors} array is null,
     * or {@code cycleMethod} is null
     * @throws IllegalArgumentException
     * if start and end points are the same points,
     * or {@code fractions.length != colors.length},
     * or {@code colors} is less than 2 in size,
     * or a {@code fractions} value is less than 0.0 or greater than 1.0,
     * or the {@code fractions} are not provided in strictly increasing order
     */
    public LinearGradientPaint(Point2D start, Point2D end,
                               float[] fractions, Color[] colors,
                               CycleMethod cycleMethod)
    {
        this(start, end,
             fractions, colors,
             cycleMethod,
             ColorSpaceType.SRGB,
             new AffineTransform());
    }

    
Constructs a LinearGradientPaint. 
Params:
  • start – the gradient axis start Point2D in user space
  • end – the gradient axis end Point2D in user space
  • fractions – numbers ranging from 0.0 to 1.0 specifying the
                 distribution of colors along the gradient
  • colors – array of colors corresponding to each fractional value
  • cycleMethod – either NO_CYCLE, REFLECT, or REPEAT
  • colorSpace – which color space to use for interpolation, either SRGB or LINEAR_RGB
  • gradientTransform – transform to apply to the gradient
Throws:
  • NullPointerException –  if one of the points is null, or fractions array is null, or colors array is null, or cycleMethod is null, or colorSpace is null, or gradientTransform is null
  • IllegalArgumentException –  if start and end points are the same points, or fractions.length != colors.length, or colors is less than 2 in size, or a fractions value is less than 0.0 or greater than 1.0, or the fractions are not provided in strictly increasing order
/**
     * Constructs a {@code LinearGradientPaint}.
     *
     * @param start the gradient axis start {@code Point2D} in user space
     * @param end the gradient axis end {@code Point2D} in user space
     * @param fractions numbers ranging from 0.0 to 1.0 specifying the
     *                  distribution of colors along the gradient
     * @param colors array of colors corresponding to each fractional value
     * @param cycleMethod either {@code NO_CYCLE}, {@code REFLECT},
     *                    or {@code REPEAT}
     * @param colorSpace which color space to use for interpolation,
     *                   either {@code SRGB} or {@code LINEAR_RGB}
     * @param gradientTransform transform to apply to the gradient
     *
     * @throws NullPointerException
     * if one of the points is null,
     * or {@code fractions} array is null,
     * or {@code colors} array is null,
     * or {@code cycleMethod} is null,
     * or {@code colorSpace} is null,
     * or {@code gradientTransform} is null
     * @throws IllegalArgumentException
     * if start and end points are the same points,
     * or {@code fractions.length != colors.length},
     * or {@code colors} is less than 2 in size,
     * or a {@code fractions} value is less than 0.0 or greater than 1.0,
     * or the {@code fractions} are not provided in strictly increasing order
     */
    @ConstructorProperties({ "startPoint", "endPoint", "fractions", "colors", "cycleMethod", "colorSpace", "transform" })
    public LinearGradientPaint(Point2D start, Point2D end,
                               float[] fractions, Color[] colors,
                               CycleMethod cycleMethod,
                               ColorSpaceType colorSpace,
                               AffineTransform gradientTransform)
    {
        super(fractions, colors, cycleMethod, colorSpace, gradientTransform);

        // check input parameters
        if (start == null || end == null) {
            throw new NullPointerException("Start and end points must be" +
                                           "non-null");
        }

        if (start.equals(end)) {
            throw new IllegalArgumentException("Start point cannot equal" +
                                               "endpoint");
        }

        // copy the points...
        this.start = new Point2D.Double(start.getX(), start.getY());
        this.end = new Point2D.Double(end.getX(), end.getY());
    }

    
Creates and returns a PaintContext used to generate a linear color gradient pattern. See the specification of the method in the Paint interface for information on null parameter handling. 
Params:
  • cm – the preferred ColorModel which represents the most convenient format for the caller to receive the pixel data, or null if there is no preference.
  • deviceBounds – the device space bounding box
                    of the graphics primitive being rendered.
  • userBounds – the user space bounding box
                  of the graphics primitive being rendered.
  • transform – the AffineTransform from user space into device space.
  • hints – the set of hints that the context object can use to
             choose between rendering alternatives.
See Also:
Returns:the PaintContext for generating color patterns.
/**
     * Creates and returns a {@link PaintContext} used to
     * generate a linear color gradient pattern.
     * See the {@link Paint#createContext specification} of the
     * method in the {@link Paint} interface for information
     * on null parameter handling.
     *
     * @param cm the preferred {@link ColorModel} which represents the most convenient
     *           format for the caller to receive the pixel data, or {@code null}
     *           if there is no preference.
     * @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 transform the {@link AffineTransform} from user
     *              space into device space.
     * @param hints the set of hints that the context object can use to
     *              choose between rendering alternatives.
     * @return the {@code PaintContext} for
     *         generating color patterns.
     * @see Paint
     * @see PaintContext
     * @see ColorModel
     * @see Rectangle
     * @see Rectangle2D
     * @see AffineTransform
     * @see RenderingHints
     */
    public PaintContext createContext(ColorModel cm,
                                      Rectangle deviceBounds,
                                      Rectangle2D userBounds,
                                      AffineTransform transform,
                                      RenderingHints hints)
    {
        // avoid modifying the user's transform...
        transform = new AffineTransform(transform);
        // incorporate the gradient transform
        transform.concatenate(gradientTransform);

        if ((fractions.length == 2) &&
            (cycleMethod != CycleMethod.REPEAT) &&
            (colorSpace == ColorSpaceType.SRGB))
        {
            // faster to use the basic GradientPaintContext for this
            // common case
            boolean cyclic = (cycleMethod != CycleMethod.NO_CYCLE);
            return new GradientPaintContext(cm, start, end,
                                            transform,
                                            colors[0], colors[1],
                                            cyclic);
        } else {
            return new LinearGradientPaintContext(this, cm,
                                                  deviceBounds, userBounds,
                                                  transform, hints,
                                                  start, end,
                                                  fractions, colors,
                                                  cycleMethod, colorSpace);
        }
    }

    
Returns a copy of the start point of the gradient axis.

Returns:a Point2D object that is a copy of the point that anchors the first color of this LinearGradientPaint
/**
     * Returns a copy of the start point of the gradient axis.
     *
     * @return a {@code Point2D} object that is a copy of the point
     * that anchors the first color of this {@code LinearGradientPaint}
     */
    public Point2D getStartPoint() {
        return new Point2D.Double(start.getX(), start.getY());
    }

    
Returns a copy of the end point of the gradient axis.

Returns:a Point2D object that is a copy of the point that anchors the last color of this LinearGradientPaint
/**
     * Returns a copy of the end point of the gradient axis.
     *
     * @return a {@code Point2D} object that is a copy of the point
     * that anchors the last color of this {@code LinearGradientPaint}
     */
    public Point2D getEndPoint() {
        return new Point2D.Double(end.getX(), end.getY());
    }
}