BATTLECAM

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BATTLECAM A Dynamic Camera System for Real-Time
Strategy Games

• Yangli Hector Yee
• Graphics Programmer, Petroglyph
• hector_at_petroglyphgames.com
• Elie Arabian
• Lead Artist, Petroglyph
• elie_at_petroglyphgames.com

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Overview

• Background
• Theory
• Implementation
• Hacks
• Cinematic Shots
• Question Answers

3
Background History

• RTS Birds Eye (Dune 2)
• First Person (Dungeon Keeper)
• Scripted Actor Camera (Warcraft 3)
• Unscripted Actor, Unscripted Camera (Star Wars
  Empire at War)

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Background - Problem

• Make a movie from an RTS battle
• Actors can move during shot
• Actors can die during shot
• Players can move actors
• Objects can move into camera

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Background - Solution

• Pick most interesting object
• Construct shot
• Play shot
• Fallback on death
• Pick next object
• Hijack existing camera scripting

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Theory Visual Attention

• How to pick interesting object
• Bottom Up Stimulus
• Intensity (black on white)
• Motion (moving stuff)
• Color (red on green)
• Orientation (circle in stripes)
• Top Down Goals
• Game Objectives
• Current User Selection

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Theory Bottom Up Attn.
Reference Itti L, Koch C. A Saliency-Based
Search Mechanism for Overt and Covert Shifts of
Visual Attention. Vision Research, pp. 263, Vol
40(10 - 12), 2000
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Center Surround Mechanism
Intensity Feature Maps
Lateral Inhibition
Intensity Conspicuity Maps
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Lateral Inhibition

• One signal vs similar signals

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Lateral Inhibition

• Purpose Promote areas with significantly
  conspicuous features while suppressing those that
  are non-conspicuous.

(After Inhibition)
(Before Inhibition)
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Implementation

• Game Logic Driven
• Images too expensive
• No screen space stuff
• Access to game logic info

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Implementation Data

• Game logic data (stimulus)
• Size
• Attack power
• Location
• Health
• Game logic data (goal driven)
• Current selection
• Visibility

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Computing Saliency

• E.g. Saliency_Speed for object(i)
• Saliency_speed(i) (speed(i) min_speed)/
  (max_speed min_speed)
• Normalized 0 to 1
• Three Normalization modes
• Large is important
• Small is imporant
• Closeness to mean is important

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Normalization Modes

• Large is important
• Saliency_val(i) (val(i) min_val) / (max_val
  min_val)
• Small is important
• Saliency_val(i) 1 (val(i) min_val) /
  (max_val min_val)
• Close to mean is important
• Saliency_val(i) 1 (val(i) avg_val) /
  (max_val min_val)

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Normalization settings

• Large is important
• Size
• Attack power
• Targets
• Speed
• Small is important
• Health
• Close to mean is important
• X, Y coordinate

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Lateral Inhibition

• Conspicuity value saliency_val
  (max_saliency_val min_saliency_val)
• Signals with great difference between max and min
  get boosted

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Importance

• Importance (i) Sum of conspicuity_vals
  weights
• Weight values
• Size 1.0
• Power 1.0
• X 0.5
• Y 0.5
• Health 1.0
• Targets 1.5
• Speed 1.0
• Sort list by importance

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Summary

• Compute normalized saliency
• Perform lateral inhibition
• Weighted sum
• Sort by importance

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Picking interesting object

• Pick current selected
• Pick current objects target 50 of the time
• Make interesting object list
• From list pick top 5 randomly. Reject if it was
  same type as the previous object looked at.

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Constructing Cinematics

• Local Space
• Transform object space cinematic into world
• Local Space without rotation frame
• Use translation only
• World space using reference objects
• For artist driven cinematic constructed in world
  space
• Transform to local space

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Local Space Cameras
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Flyby camera shot
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Circle camera shot
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Chase camera shot
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Hardpoint camera shot
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Frigate/Target camera shot
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Demo QA

• Thanks to
• Jim Richmond for camera system
• Kevin Prangley for illustrations
• Petroglyph staff for support
• Contact Info
• Hector at petroglyphgames dot com