The CreateRoundRectRgn function creates a rectangular region with rounded corners.
HRGN CreateRoundRectRgn(
int nLeftRect, // x-coordinate of the region's upper-left corner
int nTopRect, // y-coordinate of the region's upper-left corner
int nRightRect, // x-coordinate of the region's lower-right corner
int nBottomRect, // y-coordinate of the region's lower-right corner
int nWidthEllipse, // height of ellipse for rounded corners
int nHeightEllipse // width of ellipse for rounded corners
);
Parameters
nLeftRect : Specifies the x-coordinate of the upper-left corner of the region.
nTopRect: Specifies the y-coordinate of the upper-left corner of the region.
nRightRect : Specifies the x-coordinate of the lower-right corner of the region.
nBottomRect : Specifies the y-coordinate of the lower-right corner of the region.
nWidthEllipse : Specifies the width of the ellipse used to create the rounded corners.
nHeightEllipse : Specifies the height of the ellipse used to create the rounded corners.