Tutorials · Navigation and AI · Chapter 3

Prices and obstacles

15 minutes Uses: NavCost, NavObstacle

By the end

The carpet a road, a Nav Cost of 0.5; the mud dear, 4; and puddle, a Nav Cost of 2 inside the mud, where the two make 8
A Nav Obstacle of Radius 12 on each of the three tables, which the map grows by its clearance
What a price and an obstacle do to a way, and why a table is an obstacle and not a wall

On this page

A road
Mud and a puddle
In the way
What a price does to a way
The prices and the obstacles
Check it works

Reference

A road

Chapter 2’s map says only where a walker may go. A way over it is the cheapest one, and every cell of open floor costs the same, so the cheapest way is the shortest. A Nav Cost changes what some cells cost: a rectangle of the map priced dearer, or cheaper. The carpet is the corridor’s road, half the price of bare floor.

Select carpet, press Add component and choose NavCostComponent.
Set Size to 576, 16, the carpet’s own size, and Cost to 0.5. Leave Enabled ticked.
Press Ctrl+S.

carpet selected, the keep framed with the carpet across its middle: a rectangle with a square handle at each corner drawn exactly round the carpet; the Inspector, narrowed by its search box to cost, shows its NavCostComponent: Size 576.0 and 16.0, Cost 0.50, Enabled ticked

Size: The Nav Cost’s Size: its rectangle’s width and height in world units, centred on its node. A cell whose middle lies inside it takes its price. The carpet’s 576, 16 is the carpet picture, the corridor’s lower row from end to end bar a tile at each end.
Cost: How many times the price of open floor the Nav Cost’s cells cost a walker to cross. 1 changes nothing. Over 1 is dear: the mud’s 4 makes a way through it four times as dear as the same way on floor. Under 1 is a road: the carpet’s 0.5 makes a step on it half the price, so a way goes out of its road to use it. It must be over 0; a cost is never a wall.
Enabled: Whether the Nav Cost prices the map. Unticked, its cells cost what the floor does, and its rectangle is drawn dashed. Leave it ticked: chapter 10 switches one from a script.

Mud and a puddle

The courtyard’s mud is dear, and in it is a puddle dearer still. The puddle is a Nav Cost on a node of its own, under the mud, so it moves with it.

Select mud, press Add component and choose NavCostComponent. Set Size to 176, 32 and Cost to 4.
With mud still selected, press + Add node and choose Nav Cost. Rename it puddle: it goes under mud.
Set the puddle’s Position to 40, 0, its Size to 48, 32 and its Cost to 2.
Press Ctrl+S.
Select nav and press Bake on the strip. The status bar now counts 232 cells priced: the carpet’s and the mud’s. The overlay is drawn only while nav is selected, as in chapter 2.

The corridor’s east half and the courtyard below it, baked, seen through the game camera: the carpet along the corridor washed pink, the mud in the courtyard washed a brick red, and the puddle, a band of it toward its right end, a brighter pink; the floor round them washed pale and the walls dark; the thief stands at the courtyard’s east end — The prices on the overlay, seen through the game camera from where the thief starts: the road, the mud at `4`, and the puddle, where the mud’s `4` and the puddle’s `2` make `8`.

The puddle is 40 right of the mud’s middle and as tall as the mud, so its cells are inside the mud’s too. Where two Nav Costs overlap their prices multiply: the puddle’s cells cost 4 times 2, 8.

The price wash: How the overlay draws a priced cell, while the Nav Region is selected and baked: in a colour of its own instead of the floor’s pale one, and heavier the further its price is from 1. A dear cell washes warm, a road cool. Here the carpet washes pink, the mud a brick red and the puddle a brighter pink.

In the way

The tables are pictures: nothing tells the map they are there, and in chapter 2 a way across the hall went straight over them. A Nav Obstacle is a disc the map takes off, round its node.

Select table_west, press Add component and choose NavObstacleComponent. Set Radius to 12. Leave Enabled ticked.
Do the same on table_east and table_store.
Press Ctrl+S. Select nav and press Bake: 1340 cells blocked now, 36 more than the walls’ 1304, twelve round each table.

table_west selected, the hall round framed: a thin cyan circle round the west table with its move arrows on it, and a fainter circle round the east table beside it; the Inspector, narrowed to obstacle, shows its NavObstacleComponent: Radius 12.00, Enabled ticked

The two hall tables close, baked: round each, a block of cells filled orange, roughly round, with the obstacle’s thin circle drawn over it; the two blocks meet in their middle rows, with a gap of washed floor two cells wide above and below where they meet, and the floor round them washed pale — The two hall tables on the overlay, seen through the game camera: each disc of `12`, grown by the clearance to `15`, takes the cells whose middles it covers.

Radius: How far the Nav Obstacle reaches from its node’s middle, in world units: the cells whose middles fall inside the disc are off the map. A table is 16 wide, so 12 covers it with a little room; the region’s Clearance adds its 3, and no way comes within 15 of a table’s middle.
Enabled: Whether the Nav Obstacle blocks the map. Unticked, its disc is drawn dashed and the map walks through it. Leave it ticked: chapter 10 switches obstacles from a script, and chapter 13 saves one unticked.

This is where chapter 2’s Clearance first does something. The walls sit on the tile grid, and 3 never reached a cell middle from one. A disc is round and anywhere, and 3 more of it reaches cells that 12 alone missed.

What a price does to a way

Nothing walks the map yet: the first walker is chapter 5’s cat. What the map now offers a walker is this. From one end of the corridor to the other, the cheapest way runs along the carpet, though both ends stand on the row above it. Across the courtyard, a way from the mud’s west side to its east side goes round the mud by a dry strip, and a way from mud to mud goes round the puddle. Across the hall, a way past the tables goes round them, never within 15 of a table’s middle.

You see these ways drawn once something walks them. Walking it shows the cat’s way through the kitchen door, drawn over this map in Play, and Orders the corridor guard’s round along the carpet and the cat’s way round the west table.

The prices and the obstacles

The three prices. carpet and mud are the starter’s pictures, each given a Nav Cost; puddle is a Nav Cost node under mud. Enabled is ticked on all three.

Node	Parent	Position	Size	Cost
`carpet`	`keep`	`320`, `248`, as the starter has it	`576`, `16`	`0.5`
`mud`	`keep`	`448`, `312`, as the starter has it	`176`, `32`	`4`
`puddle`	`mud`	`40`, `0`	`48`, `32`	`2`

The three obstacles, each a Nav Obstacle on a table the starter has, Enabled ticked:

Node	Position	Radius
`table_west`	`136`, `104`	`12`
`table_east`	`168`, `104`	`12`
`table_store`	`552`, `72`	`12`