Designer's Crosshair

The cursor here is a tool rather than decoration: the native cursor is hidden and replaced by a cross, two guides spanning the frame and a chip with the coordinates. On every move the distance to every element edge is measured — left, right and centre on each axis; the nearest one within the snap radius takes the guide over, the guide turns solid and accented, and the element lights up. While no edge is near, the coordinate settles on the grid step: a free value in a layout is almost always an accident rather than a decision. A separate bar draws the measurement — the distance from the real position of the hand to the edge the crosshair snapped to. Everything is computed in the move handler, with no animation loop: between cursor moves the picture has no reason to change. The theme comes from the surroundings through light-dark().