docs: note what a flipped part does to a part attachment - #254
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A flipped part's pose is a mirror, which only a negative scale can carry. With update_scale OFF — the default — the mirror never reaches the target, and flip_h leaves a 180-degree difference in orientation on top of that. Also state that get_part_transform() stays exact when flipped, as long as rotation and scale are read as a pair.
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Description
docs/{ja,en}/workflow/usage_scripting.mddocument howSpriteStudioPartAttachment2Dcopies a part's pose — whole transform whenupdate_position/update_rotation/update_scaleare all ON, component-wise otherwise — but not what that means once the player is flipped.A flipped part's pose is a mirror, and a mirror can only be carried as a negative scale. With
update_scaleOFF, which is the default, the mirror never reaches the target, andflip_hleaves a 180-degree difference in orientation on top of that whileflip_vdoes not.Transform2Ddecomposes a mirror into a rotation plus a negative scale with the sign on the Y axis, so a horizontal mirror needs an extra half turn to fit that form and the rotation is what keeps it. Anyone attaching a muzzle or a hitbox to a character that turns around hits this on the default settings.The note also records that
get_part_transform()itself stays exact when flipped, providedget_rotation()andget_scale()are read as a pair. That is worth stating explicitly because the Unity player documents the opposite for its own API —Matrix4x4.rotationis undefined on a mirrored matrix, since a quaternion cannot represent a reflection at all. Godot'sTransform2Dcan, so the same question has opposite answers in the two players.Verified against the engine rather than reasoned about: with a part at 30 degrees,
flip_hreportsget_rotation() == 150,flip_vreports-30, both withget_scale() == (1, -1), and rotation + scale reconstruct the transform exactly in every case. Both flips together return the determinant to +1 — a real half turn, not a mirror.Documentation only. No code change, and the SDK submodule pin is untouched.
Merge order against #253 does not matter: that PR touches only
ss_player/, this one onlydocs/, and both branch from the same develop tip.