Creating and modifying curves on a computer display

Abstract

A computer-implemented method modifies a curve in response to a user action through a graphical user interface in the computer system, with the curve being defined by control points. Each of the control points is identified in response to user input as a fixed control point, a selected control point, or a free control point. A displacement of selected points is received, and a free slope control point of the curve is mapped to a point Tp on a line t. An interpolation curve IC(t) is defined on the line t, and a point Tp is projected to the value of the interpolation curve IC(t) at t equals Tp to find a scale factor. The scale factor is multiplied by the displacement of the selected points to determine the displacement of the free control point. A computer-implemented graphical user interface method creates a Bezier curve segment on a display in a computer system. A selection of a first segment end point is received through a graphical user interface in the computer system. The position of a cursor on the computer display is received as a second segment end point. The first and second slope points are calculated so that the Bezier segment defined by the first and second segment end points and the first and second slope points approximates an arc. The calculated Bezier curve segment is displayed on the computer display.