How do you reposition a cannon without losing its screen?
These answers restate the rules implemented by our open-source engine, which follows the WXF laws for movement, checkmate and both repetition rulings: a side that forces a repetition by perpetual check or perpetual chase loses rather than drawing. The chase half has not been validated against the official casebook. Where an answer refers to a specific position, that position lives on the linked reference page, where the build verifies it before publishing.
Direct answer
Move the cannon itself, not the screen. Sliding a cannon sideways along a rank, or up and down a file that isn't the one carrying its current threat, repositions it while leaving the screen in place. The trap to avoid is moving a different piece that happens to be the screen for a different reason and accidentally switching your own threat off.
Planning the move order
Before shifting other pieces around a cannon, check what line it is currently threatening down and which single piece is making that threat work. A natural-looking developing move elsewhere on the board can silently remove that screen and cost you the threat without a single piece actually being captured.
Repositioning onto a new screen
Sometimes the better plan is moving the cannon to a completely different file where a screen is already sitting in a useful spot, rather than trying to preserve the current one. This trades one threat for another and is often how a stalled cannon attack gets restarted against a different weakness.
Related questions
Can moving the screen itself ever be the right idea?
Yes, if you're deliberately switching the threat off, for instance to defuse your own cannon's check because you need the file for something else.
Is there a way to move a cannon and its screen together?
No, every move relocates exactly one piece, so coordinating the two always takes separate moves.
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