quadTo

quadTo is a function in the Qt framework, used with the QPainterPath class to append a quadratic Bézier curve segment to a path. It defines a curve from the path’s current point to a specified end point, using a single control point to shape the curve. This method is commonly employed in vector drawing and custom painting operations within Qt applications.

The typical signature is void QPainterPath::quadTo(qreal cpx, qreal cpy, qreal x, qreal y). It requires that the path has a current point, which is the starting point of the new segment. The control point is (cpx, cpy) and the end point is (x, y). After the call, the current position of the path becomes the end point. To begin a subpath, callers usually use moveTo before invoking quadTo.

Mathematically, a quadratic Bézier curve is defined by P0 (the current point), C (the control point), and P1 (the end point). The curve is given by B(t) = (1 − t)^2 P0 + 2(1 − t)t C + t^2 P1 for t in [0, 1]. The curve starts at P0 when t = 0 and ends at P1 when t = 1, with the tangent at P0 pointing toward C. Repeated quadTo calls can be composed to approximate more complex shapes.

Related methods include cubicTo, which uses two control points to form a cubic Bézier segment. quadTo is the simpler alternative for curves that require only one control point.