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pigfistEngine a distributed game Engine

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• Steven Moy

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Introduction

• The pigfistEngine is a multi-player game Engine.
• The pigfistEngine takes a distributed approach to
  take advantage of high-end systems.
• The pigfistEngine uses an adaptive strategy to
  make do with scarce resources.

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pigfistEngine Features

• Single-server, multiple-client topology
  (communications using UDP protocol)
• Runs on Windows PCs. (tested on 95, 98, NT, 2000)
• Keyboard mouse input.
• 32-bit, 3D Graphics rendered using OpenGL API
  graphics hardware.
• Rudimentary audio output.
• Automated Terrain Generation
• Visual C, using MFC

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Components Diagram

• Each of these modules operates in a separate
  thread.

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Component Interfaces

• The Network Module acts to enable communications
  between clients and the server.
• Each Network Module shares input and output
  queues with its local Physics Module.
• The Physics Module and Graphics Engine operate on
  shared data and work queues.

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Issues with Windows Threads

• Win9x NT 23 priority levels
• Win2000 32 priority levels
• Priority level is based on the process priority
  class and the threads priority level relative to
  that class.

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Issues with Distributed Gaming

• Network communications add latency from the time
  that the user manipulates the world to the time
  the user gets feedback.
• The server has the final say in changes to game
  state.

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Quality of Service Adaptations (1)

• The change in time between iterations is taken as
  a parameter in Physics Simulation calculations.
• In each iteration, calculate the new position and
  new velocity
• ?P V ?t
• ?V A ?t

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Quality of Service Adaptations (2)

• The client application extrapolates player and
  particle motion between network updates to hide
  inconsistent network communications performance.
• Changes in orientation are handled immediately by
  the client. Changes in position must be
  confirmed by the server.

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Quality of Service Adaptations (3)

• The Graphics Engine dynamically selects different
  levels of detail for rendering terrain.
  Currently, two levels of detail are supported.
• The Graphics Engine may choose different cutoff
  distances to limit the amount of terrain drawn
  each frame, and selects different levels of
  detail based on the distance from the viewer.

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Performance using LoD

• High Detail 180,000 polygons
• Low Detail 45,000 polygons
• The Graphics Engine uses a combination of these
  sets of polygons to render the scene. The
  mixture of polygons is determined by the frame
  rate.

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pigfistEngine Performance (1)

• () Separating the application into threaded
  modules allows separation of CPU-bound tasks from
  I/O-bound tasks.
• Graphical rendering may be limited by the
  capabilities of the video card and the refresh
  rate of the monitor (typically around 60-85 Hz).

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pigfistEngine Performance (2)

• (-) The pigfistEngine is a memory hog.
• The Physics Simulation and the Graphics Engine
  operate on separate copies of the world.

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Summary

• The pigfistEngine scales to allow for many users
  at one time.
• The pigfistEngine is adaptive to provide
  acceptable performance under less than ideal
  conditions.

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Related Topics

• Security against cheats
• Multiple-servers/Multiple clients