CDC::ScrollDC This method scrolls a rectangle of bits horizontally and vertically. BOOL ScrollDC( int dx, int dy, LPCRECT lpRectScroll, LPCRECT lpRectClip, CRgn* pRgnUpdate, LPRECT lpRectUpdate ); Parameters dx The number of horizontal scroll units. dy The number of vertical scroll units. lpRectScroll Pointer to the RECT structure or CRect object that contains the coordinates of the scrolling rectangle. lpRectClip Pointer to the RECT structure or CRect object that contains the coordinates of the clipping rectangle. When this rectangle is smaller than the original one pointed to by lpRectScroll, scrolling occurs only in the smaller rectangle. pRgnUpdate Identifies the region uncovered by the scrolling process. The ScrollDC function defines this region; it is not necessarily a rectangle. lpRectUpdate Pointer to the RECT structure or CRect object that receives the coordinates of the rectangle that bounds the scrolling update region. This is the largest rectangular area that requires repainting. The values in the structure or object when the function returns are in client coordinates, regardless of the mapping mode for the given device context. Return Value Nonzero if scrolling is executed; otherwise, it is zero.Res If lpRectUpdate is NULL, Windows does not compute the update rectangle. If both pRgnUpdate and lpRectUpdate are NULL, Windows does not compute the update region. If pRgnUpdate is not NULL, Windows assumes that it contains a valid pointer to the region uncovered by the scrolling process, defined by the ScrollDC method. The update region returned in lpRectUpdate can be passed to CWnd::InvalidateRgn if required.An application should use the ScrollWindow method of class CWnd when it is necessary to scroll the entire client area of a window. Otherwise, it should use ScrollDC. 很显然，可以用来滚动一个矩形的区域，如果滚动一个客户区域的话应使用ScrollWindow
是用于滚动的关键函数吗
This method scrolls a rectangle of bits horizontally and vertically. BOOL ScrollDC(
int dx,
int dy,
LPCRECT lpRectScroll,
LPCRECT lpRectClip,
CRgn* pRgnUpdate,
LPRECT lpRectUpdate );
Parameters
dx
The number of horizontal scroll units.
dy
The number of vertical scroll units.
lpRectScroll
Pointer to the RECT structure or CRect object that contains the coordinates of the scrolling rectangle.
lpRectClip
Pointer to the RECT structure or CRect object that contains the coordinates of the clipping rectangle. When this rectangle is smaller than the original one pointed to by lpRectScroll, scrolling occurs only in the smaller rectangle.
pRgnUpdate
Identifies the region uncovered by the scrolling process. The ScrollDC function defines this region; it is not necessarily a rectangle.
lpRectUpdate
Pointer to the RECT structure or CRect object that receives the coordinates of the rectangle that bounds the scrolling update region. This is the largest rectangular area that requires repainting. The values in the structure or object when the function returns are in client coordinates, regardless of the mapping mode for the given device context.
Return Value
Nonzero if scrolling is executed; otherwise, it is zero.Res
If lpRectUpdate is NULL, Windows does not compute the update rectangle. If both pRgnUpdate and lpRectUpdate are NULL, Windows does not compute the update region. If pRgnUpdate is not NULL, Windows assumes that it contains a valid pointer to the region uncovered by the scrolling process, defined by the ScrollDC method. The update region returned in lpRectUpdate can be passed to CWnd::InvalidateRgn if required.An application should use the ScrollWindow method of class CWnd when it is necessary to scroll the entire client area of a window. Otherwise, it should use ScrollDC.
很显然，可以用来滚动一个矩形的区域，如果滚动一个客户区域的话应使用ScrollWindow