Principal rays are shown for a parabolic mirror. The location and size of the object can be varied. The object can be placed on either side of the mirror (both sides are reflecting).
Note: Ray diagrams often use a horizontal ray, and a ray that passes through the focal point. While these can be a little easier to draw, they fail to show the virtual image that occurs for object distances less than a focal length, including the special case of the image made by a plane mirror (curvature = 0). For this reason, I've opted to use a horizontal ray and a ray that reflects off the center point of the mirror.