Brush alignment is particularly important on the system display where scrolling and moving are commonplace. A brush is a pattern of bits with a minimum size of 8-by-8 bits. GDI paints with a brush by repeating the pattern again and again within a given rectangle or region. If the region is moved by an arbitrary amount—for example, if the window is scrolled—and the brush is used again to filled empty areas around the original area, there is no guarantee that the original pattern and the new pattern will be aligned. For example, if the scroll moves the original filled area up one pixel, the intersection of the original area and any new painting will be out of alignment by one pixel, or bit. Depending on the pattern, this may have a undesirable visual effect.
To ensure that a brush is aligned after a window is moved, an application must take the following steps:
1.Call the SelectObject function to select a different brush.
2.Call the SetBrushOrg function to realign the current brush.
3.Call the UnrealizeObject function to realign the origin of the original brush when it is selected next.
4.Call the SelectObject function to select the original brush.