class TGDoubleSlider: public TGFrame, public TGWidget

TGDoubleSlider, TGDoubleVSlider and TGDoubleHSlider

DoubleSlider widgets allow easy selection of a min and a max value
out of a range.
DoubleSliders can be either horizontal or vertical oriented and
there is a choice of three different types of tick marks.

To change the min value press the mouse near to the left / bottom
edge of the slider.
To change the max value press the mouse near to the right / top
edge of the slider.
To change both values simultaneously press the mouse near to the
center of the slider.

TGDoubleSlider is an abstract base class. Use the concrete
TGDoubleVSlider and TGDoubleHSlider.

Dragging the slider will generate the event:
kC_VSLIDER, kSL_POS, slider id, 0  (for vertical slider)
kC_HSLIDER, kSL_POS, slider id, 0  (for horizontal slider)

Pressing the mouse will generate the event:
kC_VSLIDER, kSL_PRESS, slider id, 0  (for vertical slider)
kC_HSLIDER, kSL_PRESS, slider id, 0  (for horizontal slider)

Releasing the mouse will generate the event:
kC_VSLIDER, kSL_RELEASE, slider id, 0  (for vertical slider)
kC_HSLIDER, kSL_RELEASE, slider id, 0  (for horizontal slider)

Use the functions GetMinPosition(), GetMaxPosition() and
GetPosition() to retrieve the position of the slider.