NAME
        gradientslider.gadget -- create a slider with a range of colors as its
                                 background. (V39)

   FUNCTION
        The gradientslider gadget class is a type of non-proportional slider.
        The primary feature of the gradient slider is it's appearance. Unlike
        normal sliders, a gradient slider can display a "spread of colors" or
        "color gradient" in the slider container box. The "knob" or "thumb"
        of the slider appears to slide on top of this color gradient.

        The color gradient effect is built-up using a combination of multiple
        pens and half-tone dithering. The application must tell the slider
        exactly which pens to use in creating the gradient effect, and in
        what order to use them. Essentially, it does this by passing an
        array of pens (terminated by ~0, just like a PenSpec) to the slider.
        The first pen in the array is used as the color at the top of
        the slider (or left, if it is horizontal), and the last color in the
        array is used at the bottom (or right). The other pens will be
        used at evenly spaced intervals in between. Dithering is used to
        smoothly fade between the pens, allowing the illusion of a continuous
        change in color.

   TAGS
        GRAD_MaxVal (ULONG) - Set the maximum value that the slider can
                represent, in the range 0..$FFFF. Default for this tag is
                $FFFF. Applicability is (ISGU). (V39)

        GRAD_CurVal (ULONG) - Set or get the current value of the slider, in
                the range 0..$FFFF. Default for this tag is 0. Applicability is
                (ISGNU). (V39)

        GRAD_SkipVal (ULONG) - Set the amount by which the slider should
                advance whenever the user clicks on either side of the knob.
                Default for this tag is $1111. Applicability is (ISGU).
                (V39)

        GRAD_KnobPixels (UWORD) - Set the size of the knob in pixels.
                Default for this tag is 5. Applicability is (I).
                (V39)

        GRAD_PenArray (UWORD *) - Specifies an array of pens that the slider
                should use to create its gradient background. The array can
                contain any number of pens, and is terminated with a pen
                value of ~0. These pens can be allocated as shared, since
                their RGB value is not altered by the slider. The first pen
                is used on the top or left of the slider, and the last pen is
                used on the bottom or right. All other pens are evenly spaced
                out and used in between. Dithering is used between the pens
                to enhance the smoothness of the gradient transition.

                A NULL pen array causes the background of the slider to be
                rendered in the screen's background color. A pen array
                containing only a single pen causes the background to be
                rendered using that pen.

                Default for this tag is NULL. Applicability is (ISU).
                (V39)

        PGA_FREEDOM (ULONG) - Determines the orientation of the slider. This
                can be LORIENT_HORIZ for a horizontal slider, or LORIENT_VERT
                for a vertical one. Default for this tag is LORIENT_HORIZ.
                Applicability is (I). (V39)