Exploration and visibility

Exploration and visible units are tracked separately. map_visible_to remembers explored terrain for each civilization; each unit’s visibility byte records which civilizations can see it. Cities retain a visible_size for the human’s map display. Remembered improvement flags live on page 2.

reveal() in MAP.C fills unexplored tiles with black. Explored tiles are drawn through map_note(), which checks unit visibility before drawing foreign stacks. Debug mode xray_on bypasses these display checks.

Unit sight

unit_sight() in UNITS.C examines a unit’s neighbours, updates exploration and unit visibility, and handles contact. Ordinary sight covers the adjacent eight tiles. Unit types with sight bit 2 also examine the outer ring of a five-by-five square. For ships, these extra tiles must be Ocean; Submarines have additional visibility exceptions.

The same routine updates remembered city sizes and improvement flags for the human, cancels some destinations when units encounter one another, and adds AI targets. Sight is therefore part of movement and diplomacy as well as drawing.

Map sharing

Audience map exchanges combine exploration masks. Other events can reveal cities or terrain; their effects must be read at the relevant call site. The Great Library’s technology-sharing effect does not imply a general map-revelation effect.