/**
Provide the bitmap to use as background.
- Notice that the bitmap should be big enough to always cover the entire
- banner, e.g. for a horizontal banner with wxTOP style its width should
- be bigger than any reasonable window size.
-
- For wxLEFT orientation the bitmap is truncated from the top, for wxTOP
- and wxBOTTOM -- from the right and for wxRIGHT -- from the bottom, so
- put the most important part of the bitmap information in the opposite
- direction.
+ Notice that ideally the bitmap should be big enough to always cover the
+ entire banner, e.g. for a horizontal banner with wxTOP style its width
+ should be bigger than any reasonable window size. Otherwise the bitmap
+ is extended to cover the entire window area with a solid colour taken
+ from the bitmap pixel on the edge in which direction the extension
+ occurs so all bitmap pixels on this edge (top for wxLEFT, right for
+ wxTOP and wxBOTTOM and bottom for wxRIGHT) should have the same colour
+ to avoid jarring discontinuity.
+
+ If, on the other hand, the bitmap is bigger than the window size, then
+ it is truncated. For wxLEFT orientation the bitmap is truncated from
+ the top, for wxTOP and wxBOTTOM -- from the right and for wxRIGHT --
+ from the bottom, so put the most important part of the bitmap
+ information in the opposite direction where it will never be truncated.
If no valid background bitmap is specified, the banner draws gradient
background but if a valid bitmap is given here, the gradient is not