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UnrealGameplayAbilitySystemPresentation.pptx
- 1. GAS Building gameplay withUnreal Gameplay Ability System
- 2. Me - BenHowenstein ● Gameplay programmer ● Austin area game developer since 2014 ● Previous studios/projects ○ Arkane Austin - Prey, Mooncrash ○ Airship Syndicate - Darksiders: Genesis, Wayfinder ○ WolfEye Studios - Weird West, Unannounced Contact: ben.howenstein@gmail.com
- 3. GAS vs. CustomAbility System Considerations ● Complexity of needs ● Provides conceptual and concrete structure for major gameplay system for “free” ● Stat-driven design (ala RPG) ● What’s the inflection point? ○ Programming resources wrespect to complex system development ● Multiplayer ○ GAS provides out of the box support for replication ● Debugging ○ System introduces significant indirection which complicates debugging ■ Can be mitigated with tooling/debug support (see GAS Debugger extension)
- 4. Ability System Component Foundationof GAS implementation ● Responsible for all work wrespect to running abilities, applying effects, triggering cues, etc. Which actors need one? ● Perf implications for hundreds of ASCs - not a bottleneck in practice Possible to implement attribute support without underlying ASC ● Applicable to actors that need data but don’t require support from abilities or effects (e.g. Item class) ● Avoids small ASC performance overhead (ticking) ● Appropriate for “immutable” stats (no modification at runtime)
- 5. Principal Concepts Attributes ● Representsstate of gameplay objects ○ e.g. Health, Speed, Melee Damage, Jump Height, etc. Abilities ● Outer unit for executing gameplay logic, comprised of atomic tasks Effects ● Mechanism for modifying attributes Tags ● Represent state and trigger events Cues ● VFX/SFX - aesthetic, not meant for gameplay logic
- 6. Attributes Mechanism for exposingand manipulating object state in GAS. Features ● Organized into sets of conceptually related values ○ e.g. Locomotion, Health, Damage, etc. ● Supports initialization via hierarchical data ● Has concept of “base” and “current” value ● Allows validation pre/post update What to capture ● Philosophy: only include values that need exposure to GAS system ○ Example: locomotion ■ Max Speed, Acceleration, Max Jump Height, good candidates ■ Rotation Rate (defined in movement component), perhaps not
- 7. Data ● Defined incurve table assets ● Hierarchical name-based initialization ○ GroupName.SetName.AttributeName ■ Resolution on partial string matching ■ Group name resolved per class (defined on actor’s ASC) ○ For more details see implementation and commentary in FAttributeSetInitter::InitAttributeSetDefaults Workflow is a bit sticky when dealing with large data sets in curve table editor interface - opportunity for more seamless integration with external spreadsheet tools (don’t rely on Attributes
- 8. Attributes Considerations ● Must bedefined natively - introduces programmer dependency ● Only supports float data type
- 9. Attributes Tips ● In generalavoid setting attribute values directly - use effects instead (especially in concert with replication) ● Be careful with distinction between “base” and “current” value ○ Current value contains “temporary” modifications from duration-based and infinite effects, base value modified by instant and periodic effects ● Develop workflow for attribute data management via external spreadsheet tool ● Driving player locomotion entirely with attributes is tricky and not recommended, especially for complex logic (directional and strafe speed)
- 10. Abilities ● Comprised oftasks (work units) ● Must be granted before activation ○ Strategies for managing overlapping abilities ■ Multiple abilities with same trigger condition granted from different sources ● Pistol and sword attack abilities granted/revoked by weapon on equip ■ Use tag conditions to enforce mutual exclusivity ● Enforces rules for activation
- 11. Abilities Multiple abilities (sametrigger tags) granted from different sources (weapons) ● Pistol ● Sword
- 12. Abilities Use tag conditionsto enforce mutual exclusivity GA_Unholster ability ● Requires weapon holstered
- 13. Abilities Use tag conditionsto enforce mutual exclusivity GA_Shoot ability ● Blocked by weapon holstered
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- 16. Abilities Event-based activation ● Example:GA_Shoot ○ Tag-based trigger event defined in ability BP
- 17. Abilities ● Grouping abilities- e.g. AbilitySet type ○ Convenience for managing groups of abilities instead of granting/revoking one-by-one ● Data passing (extensible) ○ Tag that triggered ability (if applicable) ○ Instigator - who “caused” ability (i.e. character, weapon, projectile) ○ Target - who ability is activated on (i.e. character, weapon, projectile) ○ Optional objects - arbitrary UObject pointers ○ Optional data - instanced struct, useful for passing arbitrary concrete data ○ Context Handle - gameplay effect context ○ Instigator/target tags - tags present at activation time ○ Magnitude - arbitrary float value ○ Target data - struct containing information about target of ability
- 18. Effects Mechanism for modifyinggameplay attributes and tags ● Can be indefinite or duration-based ● Applied directly or in context of ability ● Not intended for gameplay (use abilities instead) Example: modifying movement speed (sprinting)
- 19. Effects GE_Sprint_Speed Speed calculation: BaseSpeed *SpeedSprintPctModifier
- 20. Effects Tips ● Pass gameplayeffect context via ability payload ● Implement non-trivial calculations in custom calculation class ○ In general don’t invoke gameplay logic during custom calculation execution
- 21. Tags Considerations ● Extensive editorsupport and validation ○ No support for string literals - all tags must be defined in config file(s)
- 22. Tags All tags storedin 2 containers on Ability System Component ○ Main container ○ Contains tags from: ■ Abilities ■ Effects ■ Loose tags ● Replicated container ○ Contains tags from: ■ Loose tags To serialize (or not)? ● Transient tags concept ● Name-based exclusion ○ e.g. Don’t save tags that start with “Ability”
- 23. Tags Example: exposing inputto GAS ● On input event add/remove loose tags corresponding to input type
- 24. Tags Tips ● In general,use tag query instead of tag container in blueprint properties - much more flexible in that it allows for complex logic beyond simple tag presence
- 25. Example - WeaponAttachment System
- 26. Example - WeaponAttachment System ● Attachment object (magazine, sight, explosive rounds, etc.) ○ On attach to weapon, apply effects and tags to character and weapon (each has its own ASC) ○ SetByCaller data is bridge between projectile definition and spawned instance ○ Target ASC: character, weapon or projectile ○ Tag and underlying attribute from weapon attachment definition ○ Gameplay effect: effect that applies set-by-caller data to spawned projectile ASC ○ GE approach supports combining weapon attachment effects - i.e. spawn a bullet that bounces, explodes on impact and applies status damage to affected targets
- 27. Example - FiringExplosive Projectile Idea ● Execute projectile fire GA ○ Spawn projectile at correct moment via anim notify gameplay event ● Apply gameplay effect(s) to projectile on spawn ○ Gameplay effect sets attributes and tags on projectile/weapon/character ■ Damage, explosion radius, etc. ● Apply gameplay effect on projectile impact ○ Apply direct damage GE to impacted target ○ Spawn explosion volume ■ Apply GE to targets in damage volume
- 28. Example - FiringExplosive Projectile ● Activate GA_Shoot ability ○ Set up target info ○ Play fire montage (based on tag lookup - depends on attachment supplied-tags) ○ Wait for “spawn projectile” gameplay event (via anim notify)
- 29. Example - FiringExplosive Projectile ● Spawn projectile ○ Apply set-by-caller gameplay effects to spawned projectile (i.e. explosion radius) ● Handle projectile impact ○ Apply direct damage GE to target (if applicable) ■ Damage formula: raw damage, status damage, explosion min/max radius, etc. taken from combination of projectile, weapon and character attributes ○ Spawn explosion damage volume using explosion radius attribute from projectile’s ASC
- 30. Resources Tools ● GAS Debuggerextension is indispensable!
- 31. Resources Documentation ● Tranek -essential reading! ● Epic
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