Appendix: glossary

This book uses these words in one sense only.

Word	What it means
Across	A place across the road, measured from its middle. Left is negative.
Along	A place along a segment, measured from its start.
Backdrop	The sky and the grass, the first thing in every frame.
Billboard	An animal drawn from an emoji's still, standing still and seen from the side, like the cows.
Carried	Kept from one step to the next. The ride carries four things: the rider, the truck, the clock and the encounter plan.
Corner	One of the points of a shape.
Critter	Any animal in the ride, from the cat to the elephant. A tree or a tower is never a critter.
Depth	How far ahead of the camera something is. Far things are painted first.
Derived	Worked out afresh in every frame, from what the ride carries and the road.
Encounter	What a segment holds for the rider to meet: a cat crossing, a bird's flight, or a quiet road.
Encounter plan	One of the four carried things: whether the encounter on the rider's segment is planned yet, and the step it starts at.
Far scenery	The sun and the mountains: a direction and a height above the horizon, and never any nearer.
Frame	One picture of the ride, for one step.
Invariant	A fact that holds whenever the program is right, such as a share lying between 0 and 1. The ride enforces each one with a `crash`.
Kind	Which sort of thing something is, like `Conifer`, and the type a `Geom.Placed` carries.
Near plane	The closest the camera can see, 0.4 metres ahead. A sighting refuses a thing whose foot is short of it, and a line or face that crosses it is cut there.
Picture	Everything on the screen in one frame.
Placed	Put on the road, measured `along` and `across` a segment, and `lift` off the ground.
Polygon	A shape of any number of corners but three or four, which are triangles and quads.
Rendering	A sprite with its depth, a `Rendered`.
Route	The list of segments that makes up the whole ride.
Segment	One stretch of road, from one bend to the next.
Shape	One item in a frame's list, such as a triangle, a disc or a polygon.
Sighting	A thing's spot and its kind, for one frame: a `Pipeline.Sighted`.
Solid	A thing whose every corner has its own place along, across and above the road, like the truck.
Spot	Where a thing stands in one frame, seen from the camera: a `Spot`.
Sprite	How one thing looks in one frame: its shapes, a `Sprite`.
Step	One tick of the ride. Each step has one frame.
Still	An animal's drawing, as polygons in units of its own height.
Tier	One layer of a conifer's crown.