Instructions: - Drag endpoints A (red) or B (blue) to reposition them. The other endpoint is recalculated so that the bar (A–B) stays the same length and still passes through M(t) (green). - Use the slider to move M along the Bézier curve. A/B adjust accordingly to keep the bar going through M(t). - The control points P0, P1, P2, P3 are shown in gray, along with the Bézier curve (black).

If you want a truly dynamic “drag A/B and the solver automatically finds t,” you’ll need an iterative approach. This example keeps it simpler by letting you set t via the slider.