The BUMPDATA structure contains information about the bump map parameter.
If the bTile member is set to TRUE, the nXOffset and nYOffset members represent the offset in the bump image. If there is a region on the bump image, this region rectangle will represent the bump bitmap.
If the bTile member is set to FALSE, the nXOffset and nYOffset members represent the position in the bump image. If a region is defined for either the bump or destination bitmap, or both bitmaps, the effect applies only to the intersection of regions.
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