Wall Building for RTS Games - PowerPoint PPT Presentation

Loading...

PPT – Wall Building for RTS Games PowerPoint presentation | free to download - id: 57b9c3-ZDZmN



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

Wall Building for RTS Games

Description:

Wall Building for RTS Games Patrick Schmid Age of Empires Age of Empires Stronghold Walls Walls Barbed wire Fences Sandbags Force fields Intelligent Wall Placement ... – PowerPoint PPT presentation

Number of Views:48
Avg rating:3.0/5.0
Slides: 37
Provided by: PatrickS161
Category:
Tags: rts | building | fire | games | wall

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Wall Building for RTS Games


1
Wall Building for RTS Games
  • Patrick Schmid

2
Age of Empires
3
Age of Empires
4
Stronghold
5
Walls
  • Walls
  • Barbed wire
  • Fences
  • Sandbags
  • Force fields

6
Intelligent Wall Placement
  • Locations to protect
  • Use natural barriers
  • Wall cost
  • Distance from a given location
  • Size of protected area

7
Possible Solutions
  • Build rectangular wall
  • Add walls to level via map editor
  • Wall-building algorithm

8
Problem Definition
  • Protect a given location by blocking the movement
    of enemy units
  • Implies
  • Block all access routes
  • No breaks

9
Preliminaries
  • Restricted to tile-based maps
  • Obstruction footprints confined to tiles
  • Wall segment
  • Passive defensive structure
  • Blocks unit movement over a single tile
  • Two wall segments are adjacent when they touch
    along the edges (not diagonals)
  • Four adjacent wall segments (neighbors) for each
    free standing wall segment
  • Each wall segment of a wall has two neighbors

10
Definitions
  • A wall is a set of wall segments connected
    together in such a way that
  • Every wall segments has exactly two unique
    neighbors (? wall segments linked in circular
    fashion)
  • At least one interior tile (tile inside the
    walled-off area)
  • All interior tiles (interior area) are connected
    through edges (not diagonally).

11
Examples
12
Acceptance Criteria
  • Minimum / maximum distance from location to
    protect
  • Minimum / maximum number of interior tiles
  • Maximum number of wall segments (cost of building
    wall)

13
Definition of Problem
  • On a given tile map, build a wall that fits the
    definition, protects the given location, and
    meets the given acceptance criteria.

14
Wall-building algorithm
  • Starting location (given) that needs to be
    protected
  • Apply an initial wall around this location
  • Move wall outwards greedily remove an existing
    wall segment and place it in a different
    location, so that
  • Net gain of exactly one interior tile
  • Resulting wall still meets the wall definition
  • Some moves might require addition of extra wall
    segments
  • Stop when acceptance criteria are met

15
Possible wall segments
16
Possible moves
17
Does this work?
  • Every group allows 17 possible moves 68
    possible moves
  • Common patterns can be used to reduce number of
    cases
  • Natural barriers act similarly to wall segments
  • Natural barriers will greatly increase the number
    of possible moves
  • ? Large number of moves

18
Is there a better way?
  • Instead of expanding wall, expand interior area
  • Once expansion is done, generate wall around
    interior area

19
Definitions
  • Node representation of the smallest area, e.g.
    a tile or a waypoint, that can be obstructed by
    the placement of game objects
  • Graph with every edge connecting two nodes
  • Edge defines path units can take
  • Nodes sharing same edge are called adjacent

20
Definitions (cont.)
  • A node can have any number of adjacent nodes
  • A wall segment that is part of a wall still only
    has two neighbors
  • Interior tile ? interior node
  • Interior area ? set of interior nodes
  • Starting location ? starting node
  • Move ? process of adding new nodes to the
    interior area

21
New wall-building algorithm
  • Start with starting node
  • Expand interior area by adding one node per step
  • Select the node to add using a greedy methodology
    (? heuristic function)
  • Stop when acceptance criteria are met

22
Data structures
  • Closed list
  • Nodes in the interior area
  • Open list
  • Nodes bordering the interior area
  • Ranked by heuristic function
  • After node was moved to closed list, add new
    neighboring nodes

23
(No Transcript)
24
Traversal Function
  • Get all successor nodes for a particular node
  • Power to block individual node to prevent the
    interior area from spreading into undesirable
    areas
  • Frequently used by heuristic function to get list
    of successor nodes for cost calculation

25
Heuristic Function
  • f(n) is cost function representing the cost of
    adding node n to interior area
  • c is a constant larger than the maximum possible
    distance from the starting node
  • w(n) is the cost of walling off node n
  • d(n) is the distance from node n to the starting
    node

26
w(n)
  • Number of wall segments needed to keep the new
    node walled off from the outside area
  • Only w(n) generates asymmetric walls stretching
    in only one direction
  • Why?
  • List of successor nodes tends to be arranged in a
    certain order.
  • Beginning of list gets preference over nodes with
    same cost further down the list
  • Leads to expansion in general direction of
    successor node at the top of the list

27
d(n)
  • Add distance from starting node
  • Maximize the minimum wall distance from the
    starting node for same wall cost ? good for
    defensive purposes
  • Distance-related part has to be less significant
    than portion related to walling-off
  • Achieve this by multiplying cost of walling off
    with the maximum distance (c)

28
Minimum distance
  • Gives priority (0) to the nodes closer than the
    required minimum distance
  • Need to adjust acceptance function to require
    that all nodes have reached minimum distance
  • Used to protected important location, e.g.
    building, from enemy fire

29
What about natural barriers?
  • Traversal has to ignore natural barriers
  • Heuristic function needs to treat barriers as
    free wall segments and ignore them in the
    calculation of w(n)
  • Efficient implementation Change node traversal
    to ignore barriers

30
Map Edges?
  • Inaccessible, maybe even permanent fog of war
  • Requires impassable terrain around them
  • Treated as natural barriers
  • Embraced as part of game play
  • Traversal cannot find nodes past the map edges
  • Heuristic function has no cost for those nodes
  • Area past the edges treated as invisible natural
    barrier

31
Maximum Distance?
  • Do not let open nodes at maximum distance become
    interior nodes
  • Undermines functionality of open list!
  • Introduce maximum distance list
  • Holds nodes located at max distance
  • Before adding a node to open list, check its
    distance
  • If equal to max distance, add it to max distance
    list
  • Upon completion, merge open and max distance list
    to get final solution
  • Used to place wall within manageable distance, or
    ensure protective cover of tower fire

32
Doors and Gates?
  • A wall without doors and gates is not that
    useful!
  • Simply place gates at evenly spaced locations in
    the wall
  • Dumb solution
  • Might place a gate right in front of a natural
    barrier
  • Might not get us to all interesting locations
  • Smart solution Create paths from starting
    location to interesting outside locations. Where
    path and wall intersect, place a gate.

33
Diagonal Walls?
  • Walls might be connectable diagonally
  • Cost function needs to ignore cost of walling off
    a diagonal direction
  • Diagonal successor nodes may not be added to open
    list

34
Demonstration
35
Actual Games
  • Author of chapter (Mario Grimani) worked on
  • Age of Empires II The Age of Kings
  • Age of Empires II The Conquerors
  • Age of Mythology
  • Sovereign
  • Everquest II

36
Reference
  • Mario Grimani Wall Building for RTS Games. AI
    Game Programming Wisdom 2
About PowerShow.com