The ArcTo function draws an elliptical arc.
The AngleArc function draws a line segment and an arc. The line segment is drawn from the current position to the beginning of the arc. The arc is drawn along the perimeter of a circle with the given radius and center. The length of the arc is defined by the given start and sweep angles.
The AdjustWindowRectEx function calculates the required size of the window rectangle, based on the desired size of the client rectangle. The window rectangle can then be passed to the CreateWindowEx function to create a window whose client area is the desired size.