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CWnd::ScrollWindowEx 

Scrolls the contents of a window's client area.


int ScrollWindowEx(
   int dx,
   int dy,
   LPCRECT lpRectScroll,
   LPCRECT lpRectClip,
   CRgn* prgnUpdate,
   LPRECT lpRectUpdate,
   UINT flags 
); 

Parameters

dx

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

dy

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

lpRectScroll

Points to a RECT structure that specifies the portion of the client area to be scrolled. If this parameter is NULL, the entire client area is scrolled.

lpRectClip

Points to a RECT structure that specifies the clipping rectangle to scroll. This structure takes precedence over the rectangle pointed to by lpRectScroll. Only bits inside this rectangle are scrolled. Bits outside this rectangle are not affected even if they are in the lpRectScroll rectangle. If this parameter is NULL, no clipping is performed on the scroll rectangle.

prgnUpdate

Identifies the region that is modified to hold the region invalidated by scrolling. This parameter may be NULL.

lpRectUpdate

Points to a RECT structure that will receive the boundaries of the rectangle invalidated by scrolling. This parameter may be NULL.

flags

Can have one of the following values:

  • SW_ERASE   When specified with SW_INVALIDATE, erases the newly invalidated region by sending a WM_ERASEBKGND message to the window.

  • SW_INVALIDATE   Invalidates the region identified by prgnUpdate after scrolling.

  • SW_SCROLLCHILDREN   Scrolls all child windows that intersect the rectangle pointed to by lpRectScroll by the number of pixels specified in dx and dy. Windows sends a WM_MOVE message to all child windows that intersect lpRectScroll, even if they do not move. The caret is repositioned when a child window is scrolled and the cursor rectangle intersects the scroll rectangle.

The return value is SIMPLEREGION (rectangular invalidated region), COMPLEXREGION (nonrectangular invalidated region; overlapping rectangles), or NULLREGION (no invalidated region), if the function is successful; otherwise the return value is ERROR.

This function is similar to the ScrollWindow function, with some additional features.

If SW_INVALIDATE and SW_ERASE are not specified, the ScrollWindowEx member function does not invalidate the area that is scrolled away from. If either of these flags is set, ScrollWindowEx invalidates this area. The area is not updated until the application calls the UpdateWindow member function, calls the RedrawWindow member function (specifying RDW_UPDATENOW or RDW_ERASENOW), or retrieves the WM_PAINT message from the application queue.

If the window has the WS_CLIPCHILDREN style, the returned areas specified by prgnUpdate and lpRectUpdate represent the total area of the scrolled window that must be updated, including any areas in child windows that need updating.

If the SW_SCROLLCHILDREN flag is specified, Windows will not properly update the screen if part of a child window is scrolled. The part of the scrolled child window that lies outside the source rectangle will not be erased and will not be redrawn properly in its new destination. Use the DeferWindowPos Windows function to move child windows that do not lie completely within the lpRectScroll rectangle. The cursor is repositioned if the SW_SCROLLCHILDREN flag is set and the caret rectangle intersects the scroll rectangle.

All input and output coordinates (for lpRectScroll, lpRectClip, lpRectUpdate, and prgnUpdate) are assumed to be in client coordinates, regardless of whether the window has the CS_OWNDC or CS_CLASSDC class style. Use the LPtoDP and DPtoLP Windows functions to convert to and from logical coordinates, if necessary.

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