java.awt

Class RadialGradientPaint

  • All Implemented Interfaces:
    Paint, Transparency 

    public final class RadialGradientPaint
extends MultipleGradientPaint
    The RadialGradientPaint class provides a way to fill a shape with a circular radial color gradient pattern. The user may specify 2 or more gradient colors, and this paint will provide an interpolation between each color.

    The user must specify the circle controlling the gradient pattern, which is described by a center point and a radius. The user can also specify a separate focus point within that circle, which controls the location of the first color of the gradient. By default the focus is set to be the center of the circle.

    This paint will map the first color of the gradient to the focus point, and the last color to the perimeter of the circle, interpolating smoothly for any in-between colors specified by the user. Any line drawn from the focus point to the circumference will thus span all the gradient colors.

    Specifying a focus point outside of the radius of the circle will cause the rings of the gradient pattern to be centered on the point just inside the edge of the circle in the direction of the focus point. The rendering will internally use this modified location as if it were the specified focus point.

    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 RadialGradientPaint object takes when it is filling the space outside the circle's radius by setting CycleMethod to either REFLECTION or REPEAT. The gradient color proportions are equal for any particular line drawn from the focus point. The following figure shows that the distance AB is equal to the distance BC, and the distance AD is equal to the distance DE.

    image showing the distance AB=BC, and AD=DE
    If the gradient and graphics rendering transforms are uniformly scaled and the user sets the focus so that it coincides with the center of the circle, the gradient color proportions are equal for any line drawn from the center. The following figure shows the distances AB, BC, AD, and DE. They are all equal.
    image showing the distance of AB, BC, AD, and DE are all equal
    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 the last keyframe color 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 RadialGradientPaint, where the center and focus points are the same: 

         Point2D center = new Point2D.Float(50, 50);
     float radius = 25;
     float[] dist = {0.0f, 0.2f, 1.0f};
     Color[] colors = {Color.RED, Color.WHITE, Color.BLUE};
     RadialGradientPaint p =
         new RadialGradientPaint(center, radius, dist, colors);

    This image demonstrates the example code above, with default (centered) focus for each of the three cycle methods:

    image showing the output of the sameple code

    It is also possible to specify a non-centered focus point, as in the following code: 

         Point2D center = new Point2D.Float(50, 50);
     float radius = 25;
     Point2D focus = new Point2D.Float(40, 40);
     float[] dist = {0.0f, 0.2f, 1.0f};
     Color[] colors = {Color.RED, Color.WHITE, Color.BLUE};
     RadialGradientPaint p =
         new RadialGradientPaint(center, radius, focus,
                                 dist, colors,
                                 CycleMethod.NO_CYCLE);

    This image demonstrates the previous example code, with non-centered focus for each of the three cycle methods:

    image showing the output of the sample code
    Since:
    1.6
    See Also:
    Paint, Graphics2D.setPaint(java.awt.Paint)

    • Constructor Detail

      • RadialGradientPaint

        public RadialGradientPaint(float cx,
                           float cy,
                           float radius,
                           float[] fractions,
                           Color[] colors)
        Constructs a RadialGradientPaint with a default NO_CYCLE repeating method and SRGB color space, using the center as the focus point.
        Parameters:
        cx - the X coordinate in user space of the center point of the circle defining the gradient. The last color of the gradient is mapped to the perimeter of this circle.
        cy - the Y coordinate in user space of the center point of the circle defining the gradient. The last color of the gradient is mapped to the perimeter of this circle.
        radius - the radius of the circle defining the extents of the color gradient
        fractions - numbers ranging from 0.0 to 1.0 specifying the distribution of colors along the gradient
        colors - array of colors to use in the gradient. The first color is used at the focus point, the last color around the perimeter of the circle.
        Throws:
        NullPointerException - if fractions array is null, or colors array is null
        IllegalArgumentException - if radius is non-positive, 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

      • RadialGradientPaint

        public RadialGradientPaint(Point2D center,
                           float radius,
                           float[] fractions,
                           Color[] colors)
        Constructs a RadialGradientPaint with a default NO_CYCLE repeating method and SRGB color space, using the center as the focus point.
        Parameters:
        center - the center point, in user space, of the circle defining the gradient
        radius - the radius of the circle defining the extents of the color gradient
        fractions - numbers ranging from 0.0 to 1.0 specifying the distribution of colors along the gradient
        colors - array of colors to use in the gradient. The first color is used at the focus point, the last color around the perimeter of the circle.
        Throws:
        NullPointerException - if center point is null, or fractions array is null, or colors array is null
        IllegalArgumentException - if radius is non-positive, 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

      • RadialGradientPaint

        public RadialGradientPaint(float cx,
                           float cy,
                           float radius,
                           float[] fractions,
                           Color[] colors,
                           MultipleGradientPaint.CycleMethod cycleMethod)
        Constructs a RadialGradientPaint with a default SRGB color space, using the center as the focus point.
        Parameters:
        cx - the X coordinate in user space of the center point of the circle defining the gradient. The last color of the gradient is mapped to the perimeter of this circle.
        cy - the Y coordinate in user space of the center point of the circle defining the gradient. The last color of the gradient is mapped to the perimeter of this circle.
        radius - the radius of the circle defining the extents of the color gradient
        fractions - numbers ranging from 0.0 to 1.0 specifying the distribution of colors along the gradient
        colors - array of colors to use in the gradient. The first color is used at the focus point, the last color around the perimeter of the circle.
        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 radius is non-positive, 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

      • RadialGradientPaint

        public RadialGradientPaint(Point2D center,
                           float radius,
                           float[] fractions,
                           Color[] colors,
                           MultipleGradientPaint.CycleMethod cycleMethod)
        Constructs a RadialGradientPaint with a default SRGB color space, using the center as the focus point.
        Parameters:
        center - the center point, in user space, of the circle defining the gradient
        radius - the radius of the circle defining the extents of the color gradient
        fractions - numbers ranging from 0.0 to 1.0 specifying the distribution of colors along the gradient
        colors - array of colors to use in the gradient. The first color is used at the focus point, the last color around the perimeter of the circle.
        cycleMethod - either NO_CYCLE, REFLECT, or REPEAT
        Throws:
        NullPointerException - if center point is null, or fractions array is null, or colors array is null, or cycleMethod is null
        IllegalArgumentException - if radius is non-positive, 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

      • RadialGradientPaint

        public RadialGradientPaint(float cx,
                           float cy,
                           float radius,
                           float fx,
                           float fy,
                           float[] fractions,
                           Color[] colors,
                           MultipleGradientPaint.CycleMethod cycleMethod)
        Constructs a RadialGradientPaint with a default SRGB color space.
        Parameters:
        cx - the X coordinate in user space of the center point of the circle defining the gradient. The last color of the gradient is mapped to the perimeter of this circle.
        cy - the Y coordinate in user space of the center point of the circle defining the gradient. The last color of the gradient is mapped to the perimeter of this circle.
        radius - the radius of the circle defining the extents of the color gradient
        fx - the X coordinate of the point in user space to which the first color is mapped
        fy - the Y coordinate of the point in user space to which the first color is mapped
        fractions - numbers ranging from 0.0 to 1.0 specifying the distribution of colors along the gradient
        colors - array of colors to use in the gradient. The first color is used at the focus point, the last color around the perimeter of the circle.
        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 radius is non-positive, 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

      • RadialGradientPaint

        public RadialGradientPaint(Point2D center,
                           float radius,
                           Point2D focus,
                           float[] fractions,
                           Color[] colors,
                           MultipleGradientPaint.CycleMethod cycleMethod)
        Constructs a RadialGradientPaint with a default SRGB color space.
        Parameters:
        center - the center point, in user space, of the circle defining the gradient. The last color of the gradient is mapped to the perimeter of this circle.
        radius - the radius of the circle defining the extents of the color gradient
        focus - the point in user space to which the first color is mapped
        fractions - numbers ranging from 0.0 to 1.0 specifying the distribution of colors along the gradient
        colors - array of colors to use in the gradient. The first color is used at the focus point, the last color around the perimeter of the circle.
        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 radius is non-positive, 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

      • RadialGradientPaint

        @ConstructorProperties(value={"centerPoint","radius","focusPoint","fractions","colors","cycleMethod","colorSpace","transform"})
public RadialGradientPaint(Point2D center,
                                                                                                                                                           float radius,
                                                                                                                                                           Point2D focus,
                                                                                                                                                           float[] fractions,
                                                                                                                                                           Color[] colors,
                                                                                                                                                           MultipleGradientPaint.CycleMethod cycleMethod,
                                                                                                                                                           MultipleGradientPaint.ColorSpaceType colorSpace,
                                                                                                                                                           AffineTransform gradientTransform)
        Constructs a RadialGradientPaint.
        Parameters:
        center - the center point in user space of the circle defining the gradient. The last color of the gradient is mapped to the perimeter of this circle.
        radius - the radius of the circle defining the extents of the color gradient
        focus - the point in user space to which the first color is mapped
        fractions - numbers ranging from 0.0 to 1.0 specifying the distribution of colors along the gradient
        colors - array of colors to use in the gradient. The first color is used at the focus point, the last color around the perimeter of the circle.
        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 radius is non-positive, 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

      • RadialGradientPaint

        public RadialGradientPaint(Rectangle2D gradientBounds,
                           float[] fractions,
                           Color[] colors,
                           MultipleGradientPaint.CycleMethod cycleMethod)
        Constructs a RadialGradientPaint with a default SRGB color space. The gradient circle of the RadialGradientPaint is defined by the given bounding box.

        This constructor is a more convenient way to express the following (equivalent) code:

             double gw = gradientBounds.getWidth();
     double gh = gradientBounds.getHeight();
     double cx = gradientBounds.getCenterX();
     double cy = gradientBounds.getCenterY();
     Point2D center = new Point2D.Double(cx, cy);

     AffineTransform gradientTransform = new AffineTransform();
     gradientTransform.translate(cx, cy);
     gradientTransform.scale(gw / 2, gh / 2);
     gradientTransform.translate(-cx, -cy);

     RadialGradientPaint gp =
         new RadialGradientPaint(center, 1.0f, center,
                                 fractions, colors,
                                 cycleMethod,
                                 ColorSpaceType.SRGB,
                                 gradientTransform);
        Parameters:
        gradientBounds - the bounding box, in user space, of the circle defining the outermost extent of the gradient
        fractions - numbers ranging from 0.0 to 1.0 specifying the distribution of colors along the gradient
        colors - array of colors to use in the gradient. The first color is used at the focus point, the last color around the perimeter of the circle.
        cycleMethod - either NO_CYCLE, REFLECT, or REPEAT
        Throws:
        NullPointerException - if gradientBounds is null, or fractions array is null, or colors array is null, or cycleMethod is null
        IllegalArgumentException - if gradientBounds is empty, 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

    • Method Detail

      • createContext

        public PaintContext createContext(ColorModel cm,
                                  Rectangle deviceBounds,
                                  Rectangle2D userBounds,
                                  AffineTransform transform,
                                  RenderingHints hints)
        Creates and returns a PaintContext used to generate a circular radial color gradient pattern. See the description of the createContext method for information on null parameter handling.
        Parameters:
        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.
        Returns:
        the PaintContext for generating color patterns.
        See Also:
        Paint, PaintContext, ColorModel, Rectangle, Rectangle2D, AffineTransform, RenderingHints

      • getCenterPoint

        public Point2D getCenterPoint()
        Returns a copy of the center point of the radial gradient.
        Returns:
        a Point2D object that is a copy of the center point

      • getFocusPoint

        public Point2D getFocusPoint()
        Returns a copy of the focus point of the radial gradient. Note that if the focus point specified when the radial gradient was constructed lies outside of the radius of the circle, this method will still return the original focus point even though the rendering may center the rings of color on a different point that lies inside the radius.
        Returns:
        a Point2D object that is a copy of the focus point

      • getRadius

        public float getRadius()
        Returns the radius of the circle defining the radial gradient.
        Returns:
        the radius of the circle defining the radial gradient