ImGuizmo scale hover/drag relies on ray-plane intersection with the
axis as plane normal; in front views (axis ⟂ camera-to-object) the
intersection numerator is identically zero, so handles can't be
grabbed and values jump randomly; axes parallel to the view have zero
screen displacement. Submodule is read-only and AxisMask can only hide
degenerate axes, not replace them.
Replace the library scale path entirely with a screen-space gizmo:
- three axis rods (line + end square) + center uniform-scale square,
constant screen size in any view
- axis drag: mouse delta projected onto the axis' screen direction
- axis pointing at camera: radial mapping (drag away = grow)
- center square: uniform scale (library MT_SCALE_XYZ semantics)
- Ctrl snapping quantizes the result; scale clamped >= 0.01
- pick suppressed while hovering/dragging the self-drawn handles
atdunbg