Rectangle functions alter and obtain information about rectangles in a window's client area. In Windows, a rectangle is defined by a RECT data structure. The structure contains two points: the upper-left and lower-right corners of the rectangle. The sides of a rectangle extend from these two points and are parallel to the x-and y-axes. The following list briefly describes each rectangle function:
| Function | Description | |
| CopyRect | Makes a copy of an existing rectangle. | |
| EqualRect | Determines whether two rectangles are equal. | |
| InflateRect | Expands or shrinks the specified rectangle. | |
| IntersectRect | Finds the intersection of two rectangles. | |
| OffsetRect | Moves a given rectangle. | |
| PtInRect | Indicates whether a specified point lies within a given rectangle. | |
| SetRectEmpty | Sets a rectangle to an empty rectangle. | |
| UnionRect | Stores the union of two rectangles. |