getPosTan

getPosTan is a method of the Android graphics class PathMeasure. It provides a way to determine a point and the direction of travel along a Path at a specific distance from the start of the path. This makes it useful for animating objects that follow a predefined path or for computing orientation along the curve.

The typical signature is getPosTan(float distance, float[] pos, float[] tan), where distance is the arc-length distance along the Path, pos is a 2-element array to receive the x and y coordinates, and tan is a 2-element array to receive the tangent vector components (dx/ds, dy/ds) at that point. The tangent vector is effectively the direction of the path at the given distance and is usually a unit vector since it corresponds to the derivative with respect to the path parameter.

The method returns a boolean indicating success. It fills pos and tan only when the requested distance lies within the length of the measured Path. If the distance is outside the path’s bounds, the method returns false and the arrays may remain unchanged.

Usage context often includes positioning a visual element along a Path while aligning its rotation with the path’s tangent, enabling smooth following motion or rotation that matches the curve’s direction. getPosTan is a core tool in 2D path animation and effects within Android’s graphics framework.

For additional details, see the PathMeasure class and the Path class in Android’s documentation.