Region functions create, alter, and retrieve information about regions. A region is an elliptical or polygonal area within a window that can be filled with graphics output. An application uses these functions in conjunction with the clipping functions to create clipping regions. (For more information about clipping functions, see the next section, “Clipping Functions.”) Following are the region functions:
| Function | Description |
| CombineRgn | Combines two existing regions into a new region. |
| CreateEllipticRgn | Creates an elliptical region. |
| CreateEllipticRgnIndirect | Creates an elliptical region. |
| CreatePolygonRgn | Creates a polygonal region. |
| CreatePolyPolygonRgn | Creates a region consisting of a series of closed polygons that are filled as though they were a single polygon. |
| CreateRectRgn | Creates a rectangular region. |
| CreateRectRgnIndirect | Creates a rectangular region. |
| CreateRoundRectRgn | Creates a rounded rectangular region. |
| EqualRgn | Determines whether two regions are identical. |
| FillRgn | Fills the given region with a brush pattern. |
| FrameRgn | Draws a border for a given region. |
| GetRgnBox | Retrieves the coordinates of the bounding rectangle of a region. |
| InvertRgn | Inverts the colors in a region. |
| OffsetRgn | Moves the given region. |
| PaintRgn | Fills the region with the selected brush pattern. |
| PtInRegion | Tests whether a point is within a region. |
| RectInRegion | Tests whether any part of a rectangle is within a region. |
| SetRectRgn | Changes a region into a specified rectangular region. |