Stromatolites accreting upward from the bottom edge of a full-bleed pane: a heightfield of columns competes for a light-occlusion clearance integral cast in a cone toward a slowly arcing light direction, so a few tall domes shade and outgrow their neighbours while a slow sea-level line periodically drowns and revives the whole front, and every ~2s the front is committed as a banded lamina stripe until the field reads like cut stromatolite rock.