[tbolis]

Problem

Moving objects and then undoing did not undo the move: the objects disappeared. There were three separate causes.

1. Straight lines. Undo set every property of the saved state, including x1, y1, x2, y2. A line stores these relative to its center, and the canvas reads them as canvas coordinates when they are set, so the line went to the top left corner (under the toolbar). Redo did the same.
2. Moving a selection of several objects. The modification was not recorded, so undo removed the last object drawn.
3. Rectangle label. The snapshot of the rectangle was the one taken when the pointer was pressed to draw it (size 0), because only the last added object was refreshed on release. Undo made the rectangle disappear and left the text box behind.

Changes

• Undo and redo set only the properties the modification changed, never the derived line points.
• A move, scale or rotate of a selection is one action for all its objects. Undo and redo discard the selection first, so each object gets its position on the canvas.
• The state an object goes back to is the one it has when the pointer is pressed on it.
• The text box of a rectangle label is recorded in the same action as the rectangle.
• A modification which changes nothing is not an action.

Files: history/SketchHistory.ts, events.ts, RectangleLabel/RectangleLabelObject.ts, CHANGELOG.md, and the new history/modifications.spec.tsx (57 tests).

Verification

• 57 new tests: lines in five directions, rectangle, circle, polygon, pencil, text, arrow, rectangle label, selections, loaded values, no-op changes. 26 of them fail on the previous code.
• Whole suite: 507 passed, on React 19 and React 18.
• Format, lint, typecheck and yarn build pass.
• In Chrome, in the showcase: move, undo and redo for rectangle, rectangle label, circle, three line variants, arrow, pencil, highlighter, polygon, and selections of two rectangles, two lines, and a line with a rectangle. All return to the exact position.

Notes

• Undo or redo of a selection move deselects the selection.
• Scale and rotate of a selection are covered by the tests, not checked in the browser.
• feat: add the bucket fill tool #214 also changes SketchHistory.ts and adds a ## 1.2.0 heading to CHANGELOG.md, so the second of the two to merge needs a conflict resolution.