target angle calculation

mouselookthrusterai.js

// Calculate normalized target vector to heading.
var globalHeading = input.faceHeading;
Vec2.setFromValues(
  targetDir,
  Math.cos( globalHeading ),
  Math.sin( globalHeading )
);

// Calculate angle between forward vector and target vector.
Mat2.multVec2( xf.rotation, LOCAL_FORWARD, forward );
var cross = targetDir[0] * forward[1] - targetDir[1] * forward[0];
var sign = cross > 0 ? -1 : 1;
var dot = Vec2.dot( targetDir, forward );
var targetAngle = sign * Math.acos( dot );