Game Technology

ELIS – Multimedia Lab

Game Technology

Game TechnologyCharles Hollemeersch

28/11/2008

• Game Engines• Rendering

• Culling• Setup• Drawing

• Phong Lighting• Physics

• Collision Detection• Forces• Integration

• Scripting• Production

Overview

28/11/2008

Simplified Game Architecture

Game Engine

SceneManager

Physics

GraphicsCard

Game Scripts

28/11/2008

• “Engine” is independent of one particular game• Scripts define individual game behavior and game play

Game “Engines”

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Engine Overview

Game Engine

SceneManager

Physics

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• Different parts of engine all need to access the “world”• Linear search of all objects is slow for large worlds• Create sub-linear structure• O(1) or O(log(n))• Hash structures• Tree structure

Need for Scene Structures

Quad Tree

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Examples of Scene Structures

Wolfenstein 3D:Regular 2D GridTomb Raider:

Regular 3D GridQuake:3D BSP, Arbitrary world geometryGTA:

Complex trees, streaming, LOD

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Engine Overview

Game Engine

SceneManager

Physics

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Renderer Overview

Renderer

Culling SetupGraphics

CardDraw

• OpenGL• DirectX

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• The scene is presented to the renderer to draw it.• Contains all objects in the game world• Sending everything to the graphics card is slow• Send only limited set of objects visible by camera

View Culling

To be culled

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• Use fast operations provided by the scene manager• Example: 2D Quad Tree

Optimizing Culling

Level1 Level2 Level3 Level…

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Renderer Overview

Renderer

CardDraw

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• Prepare data for efficient rendering• Sort objects per material• Create batches• Calculate per object shader parameters

• Send to Graphics Card for rendering

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Renderer Overview

Renderer

CardDraw

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• Recapitulation

Rendering

Texture Coordinate

Vertex

Triangle

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• Light intensity is dependent on surface normalCosine Law

Same amount light reaches both surfaces.

• Light distributed over small area.• Surface will appear bright.

• Light distributed over larger area.• Surface will appear dark

28/11/2008

Simplified Light-Surface interactions

Diffuse• Light scattered in all

directions equally.

Specular• Light reflected in one

particular direction.

Many real-life materials can be modeled by a combination of specular and diffuse models.

28/11/2008

• Based on these observations create simple ad-hoc model to calculate lighting.

Diffuse Term Specular Term

max(0, L.n) Cd Cl + max(0, R.n)e Cs Cl

Phong Lighting

Calculate area hit by light rays

Take color of surface Take color of

light sourceCheck if camera looking in reflected direction

Make the reflected beam narrow

Take color of surface

Take color of light source

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Additional lights and shadows

More than one light• Independent of each other.• Add output of Phong

equations for all lights

Shadows• Mask out contribution of

Phong equation if in shadow.

28/11/2008

• Attenuation• Further from source light gets dimmer• Theoretically infinite radius

• Light Culling• At certain point assume light level zero• Use techniques similar to view culling

Attenuation & Light Culling

28/11/2008

• We evaluate this equation to determine the lighting at a certain point.

Full equation

iii S )Cl Cs .n)R max(0, Cl Cd .n)L (max(0, i

Shadow contributionAdd all lights in scene

Phong for ith light

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Object:

Evaluate on CPU

Triangle:

Vertex:

Evaluate in vertex shader

Evaluate in pixel shader

Where to evaluate equation?

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Where to store equation parameters

• Per object

• Per pixel (in texture)

28/11/2008

• Normals are geometric property of surface

• Low poly surface: Renders fast but low lighting detail

• Normalmapping: Store approximate normals in texture

Normal/Bump mapping

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Using the GPU to evaluate model: Shaders

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Shadow Mapping

Texture: Stores length of blue arrows• Check green length to blue to determine shadows

Depth as seen from light source

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Shadow Techniques - Comparison

SM PCF 5x5 Bil.PCF 5x5 VSMStencil

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Engine Overview

Game Engine

SceneManager

Physics

28/11/2008

Physics Overview

CollisionDetection Forces Integration

28/11/2008

Physics Overview

28/11/2008

• Broad phase• Use the scene manager to determine nearby objects

• Narrow phase• Object – Object interactions• To simplify calculations, use simple shapes:

• Spheres, boxes, …

Collision Detection

28/11/2008

• Example of simplification

Collision detection – Rag Dolls

28/11/2008

Physics Overview

28/11/2008

• Forces acting on the objects are accumulated• “Traditional” forces:

• Gravity• Collisions• …

• “Simulation” forces• Collision detection• Constraints

• “Game” forces• Explosions, magic, • Not simulated correctly what looks fun

Forces

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Physics Overview

28/11/2008

• Good old Newton

• Object’s state vector is integrated using numerical integration methods• Euler• Runge Kutta

Integration

28/11/2008

• Use computational power of the GPU• Parallelize algorithms• For example:• PhysX engine by NVIDIA• Uses CUDA to drive the GPU

Physics on the GPU

28/11/2008

Engine Overview

Game Engine

SceneManager

Physics

Game Scripts

28/11/2008

Scripting

• Script programmers & technical artists• AI & Behavior• Physical properties• Animation behavior

World Objec t

Static Objec t

Birc h

Phy sic s O bj ect

Monster

Zombie

Vehicl e

Pla yer

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• “Making the game”• Use engine to create an unique game• Mainly artists, designers and script writers

Production

28/11/2008

GDD• Visual

description

• Function in game

Concept art• Han

d drawn idea

Modelling• 3D

model of object is constructed

Rigging• A

skeleton is added to the model

Animation• The

skeleton is animated

• Motion capture

Texturing• A

texture is made for the model

Integration• AI

Code• Load

assets in game

Production – Asset Pipeline

28/11/2008

• Contact:• charlesfrederik.hollemeersch@ugent.be

Questions?

Game Technology

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