A Pixel Art Editor With Bresenham Lines, Flood Fill, and Immutable Grid State The editor has six tools: pencil, eraser, flood fill, line, rectangle, and eyedropper. Each tool operates on an immutable grid — every edit returns a new 2D array. That makes undo/redo just a history stack of snapshots with no deep-copy bookkeeping per action. Pixel art editors look simple but surface a few interesti