自定义滚动条控件，利用CStatic控件派生一个自定义滚动条CCustomScroll,在CStatic控件上利用位图绘制滚动条箭头，滚动块及滚动区域-Custom scroll bar control, the use of a CStatic derived custom control scrollbar CCustomScroll, in CStatic control on the use of digital mapping