/**
* Adjusts the parent and child bone rotations so the tip of the child is as close to the target
* position as possible. The target is specified in the world coordinate system.
*
* @param child Any descendant bone of the parent.
*/
public static void apply(
Bone parent, Bone child, float targetX, float targetY, int bendDirection, float alpha) {
float childRotation = child.rotation, parentRotation = parent.rotation;
if (alpha == 0) {
child.rotationIK = childRotation;
parent.rotationIK = parentRotation;
return;
}
Vector2 position = temp;
Bone parentParent = parent.parent;
if (parentParent != null) {
parentParent.worldToLocal(position.set(targetX, targetY));
targetX = (position.x - parent.x) * parentParent.worldScaleX;
targetY = (position.y - parent.y) * parentParent.worldScaleY;
} else {
targetX -= parent.x;
targetY -= parent.y;
}
if (child.parent == parent) position.set(child.x, child.y);
else parent.worldToLocal(child.parent.localToWorld(position.set(child.x, child.y)));
float childX = position.x * parent.worldScaleX, childY = position.y * parent.worldScaleY;
float offset = (float) Math.atan2(childY, childX);
float len1 = (float) Math.sqrt(childX * childX + childY * childY),
len2 = child.data.length * child.worldScaleX;
// Based on code by Ryan Juckett with permission: Copyright (c) 2008-2009 Ryan Juckett,
// http://www.ryanjuckett.com/
float cosDenom = 2 * len1 * len2;
if (cosDenom < 0.0001f) {
child.rotationIK =
childRotation
+ ((float) Math.atan2(targetY, targetX) * radDeg - parentRotation - childRotation)
* alpha;
return;
}
float cos =
clamp(
(targetX * targetX + targetY * targetY - len1 * len1 - len2 * len2) / cosDenom, -1, 1);
float childAngle = (float) Math.acos(cos) * bendDirection;
float adjacent = len1 + len2 * cos, opposite = len2 * sin(childAngle);
float parentAngle =
(float)
Math.atan2(
targetY * adjacent - targetX * opposite, targetX * adjacent + targetY * opposite);
float rotation = (parentAngle - offset) * radDeg - parentRotation;
if (rotation > 180) rotation -= 360;
else if (rotation < -180) //
rotation += 360;
parent.rotationIK = parentRotation + rotation * alpha;
rotation = (childAngle + offset) * radDeg - childRotation;
if (rotation > 180) rotation -= 360;
else if (rotation < -180) //
rotation += 360;
child.rotationIK =
childRotation + (rotation + parent.worldRotation - child.parent.worldRotation) * alpha;
}
