ScrollDC

The ScrollDC function scrolls a rectangle of bits horizontally and vertically.

BOOL ScrollDC(

HDC hDC,	// handle of device context
int dx,	// horizontal scroll units
int dy,	// vertical scroll units
CONST RECT *lprcScroll,	// address of structure for scrolling rectangle
CONST RECT *lprcClip,	// address of structure for clipping rectangle
HRGN hrgnUpdate,	// handle of scrolling region
LPRECT lprcUpdate	// address of structure for update rectangle
);

Parameters

hDC

Identifies the device context that contains the bits to be scrolled.

dx

Specifies the amount, in device units, of horizontal scrolling. This parameter must be a negative value to scroll to the left.

dy

Specifies the amount, in device units, of vertical scrolling. This parameter must be a negative value to scroll up.

lprcScroll

Points to the RECT structure containing the coordinates of the scrolling rectangle.

lprcClip

Points to the RECT structure containing the coordinates of the clipping rectangle. Only device bits within the clipping rectangle are affected. Bits scrolled from the outside of the rectangle to the inside are painted; bits scrolled from the inside of the rectangle to the outside are not painted.

hrgnUpdate

Identifies the region uncovered by the scrolling process. ScrollDC defines this region; it is not necessarily a rectangle.

lprcUpdate

Points to the RECT structure that receives the coordinates of the rectangle bounding the scrolling update region. This is the largest rectangular area that requires repainting. When the function returns, the values in the structure are in client coordinates, regardless of the mapping mode for the specified device context. This allows applications to use the update region in a call to the InvalidateRgn function, if required.

Return Values

If the function succeeds, the return value is nonzero.

If the function fails, the return value is zero. To get extended error information, call GetLastError.

Remarks

If the lprcUpdate parameter is NULL, Windows does not compute the update rectangle. If both the hrgnUpdate and lprcUpdate parameters are NULL, Windows does not compute the update region. If hrgnUpdate is not NULL, Windows proceeds as though it contains a valid handle of the region uncovered by the scrolling process (defined by ScrollDC).

When you must scroll the entire client area of a window, use the ScrollWindow function; otherwise, use ScrollDC.

See Also

InvalidateRgn, RECT, ScrollWindow

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