Three.js ShapeGeometry rotateX mirrors Z

THREE.ShapeGeometry creates triangles in the XY plane. Rotating it onto the XZ plane with rotateX(-π/2) flips the sign of the original Y → Z mapping (Shape.y becomes -worldZ), so a floor mesh built from polygon points [x,z] ends up mirrored across the X axis from the walls drawn directly at those z coordinates. Walls and floor look offset/duplicated until you negate Z when feeding the polygon into THREE.Shape (or use rotateX(+π/2) with DoubleSide to compensate for the inverted normal).