Roche Lobe Overflow 2D: Equipotential Field & Mass-Transfer Stream

This companion view computes the same corotating-frame Roche potential as the 3D simulator, but represents it the way astronomers actually draw it in textbooks: as a 2D scalar field over the orbital plane. A grid of potential values is sampled directly (no ray-marching, no camera), rendered as a topographic map, and its critical equipotential — the true Roche-lobe boundary pinched at the L1 Lagrange point — is extracted with the marching-squares contouring algorithm instead of a 3D mesh. A mass-transfer stream is integrated on top of the field using the exact same planar gravity-plus-Coriolis equations of motion as the 3D model, since the orbital plane is an exact invariant subspace of the physics, not a simplification of it. Adjust the mass ratio, total mass, separation and donor fill factor and watch the field, the lobe outline, the L1 position and the mass-transfer stream all respond together.