Software Games Development What are 3D games

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Software Games Development What are 3D games?

• Abdennour El Rhalibi

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Part I What are 3D Games?

• Key Topics
• The games of third dimension
• The Components of DirectX
• Direct3D and todays games,
• The features of 3D games
• Hardware acceleration
• Watt A Policarpo F, (2001) 3D Games
  Real-time rendering Software technology,
  volume 1. Addison Wesley. ISBN 0201-61921-0
• Andrew Rollings, (1999) Game Architecture and
  Design, CoriolisI, SBN1576104257
• Mark DeLoura, (2000) Game Programming Gems",
  (Ed.) Charles River Media, ISBN 1584500492.

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Introduction

• The computer game world is now officially 3D.
• Action games have long existed outside the
  confines of two dimensions, but until recently, a
  vast number of games were two-dimensional, most
  notably adventure and strategy games. With the
  advent of the low-cost 3D accelerator, however,
  this has changed.
• In this lecture, we will discuss the
  three-dimensional games by covering their most
  distinguishing features.

7th Guest
Capture the Flag
Black and White
Half-life
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The State Of The Art

• The games industry has always prided itself on
  being on the cutting edge of technology.
  Whenever a new processor, graphics card, or any
  other cool peripheral appears on the market and
  needs support, the game developers are there in
  force to provide that support.
• Although game developers may perceive themselves
  as being on the cutting edge of technology, this
  position is debatable. Who is to say whether the
  latest 3D came or the latest multi-terrabyte
  database software is the most advanced?
• Undoubtedly, in terms of technical complexity, a
  database such as SQL Server 7 (for e.g.) is more
  advanced than any game currently on the market.
  But it's just not as enticing, and the coolness
  factor associated with games and game development
  only helps to feed the hype.

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The State Of The Art

• However, we can say that, although game
  developers are not on the cutting edge of
  technology, they are most definitely world
  leaders in the art of fast approximation of
  simulated real-world systems.
• Why fast approximations? Well, until home
  computers get much more powerful than they are
  today, there is no way we would be able to model
  an immersive world full of complex dynamics and
  interactions in realtime, without taking a few
  shortcuts to save time.
• Even if Moore's Law holds true, and raw computer
  processing power doubles every 18 months or so,
  it is doubtful that anybody will be able to make
  a truly accurate to-the-molecule simulation of a
  world for a very long time.  
• As computers get faster and faster, these
  approximations will become increasingly accurate.
  Nowhere is this more evident than in the
  graphics engines for today's games. The lineage
  of the 3D graphics engine can be traced back to
  the early days.

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The Rise and Fall of the 3D Engine

• The first famous 3D game was Battlezone, as shown
  Figure 1, in the arcades. This simple tank
  simulation used low-polygon-count wireframe
  graphics to portray a simple landscape
  interspersed with cubes, pyramids, and tanks.
• No hidden-line removal was attempted (that is,
  objects appeared as if they were made of glass
  and you could see the hidden edges on the far
  side of the object).

Fig. 1 - Battlezone
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The Rise and Fall of the 3D Engine

• The next famous one was the BBC version of Elite,
  as shown in Figure 2, by David Braben and Ian
  Bell.
• The 3D engine represented each star system as a
  single sun (as a filled circle with perturbed
  edges) and a single planet (as an outlined
  circle). Ships were drawn in wireframe and
  benefited from intraobject hidden-line removal
  (that is, you couldn't see the far side of a ship
  through its infrastructure, but you would be able
  to see if another ship was behind it).

Fig. 2 BBC Elite
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The Rise and Fall of the 3D Engine

• As processing power increased, so did the number
  of polygons used, as well as the complexity of
  the drawing techniques.
• First came filled polygons, such as those seen in
  the Archimedes version of Elite, as shown in
  Figure 3. These polygons were simply colored flat
  shade of a single color.

Fig. 3 Archimedes Elite
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The Rise and Fall of the 3D Engine

• Soon after, simple flat shading was added to the
  polygons, and these would change in illumination
  according to a light source, as demonstrated in
  Zarch, and shown in Figure 4.
• This was usually a simple directional light
  source anything else would have been too
  computationally expensive.

Fig. 4 Zarch
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The Rise and Fall of the 3D Engine

• This was closely followed by Gouraud shading, a
  technique whereby the illumination was calculated
  at the vertices of the polygon and simply
  linearly interpolated over the interior of the
  polygon, as in Little Big Adventure (known as
  Relentless in the U.S.) shown in Figure 5.

Fig. 5 Little big adventure
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The Rise and Fall of the 3D Engine
The Rise and Fall of the 3D Engine

• The next development in the saga of the polygon
  was texture mapping projecting a picture onto
  the surface of the polygon so that it appeared
  that the polygon was textured.
• Ultima Underworld II, as shown in Figure 6, was
  one of the first examples of this.

Fig. 6 Ultima Underworld II
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The Rise and Fall of the 3D Engine
The Rise and Fall of the 3D Engine

• Later developments - such as Wolfenstein 3D
  (which introduced ray casting) shown in Figure 7,
  Doom (which introduced binary space partitioning
  (BSP) trees) shown in Figure 8 - brought more
  advances to light sources, with explosions
  providing directional point sources, and laser
  fire dynamically lighting walls as it streaked
  past.

Fig. 8 - Doom
Fig. 7 Wolfenstein 3D
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The Rise and Fall of the 3D Engine

• At this stage, 3D was still the exception rather
  than the rule. Most games were still being
  developed in 2D, and 3D was only just beginning
  to become the mainstream.
• Quake (as shown in Figure 9) heralded in this new
  era of game development.

Fig. 9 - Quake
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The Rise and Fall of the 3D Engine

• What caused the great turnaround was the
  introduction of the first 3D accelerators into
  the market.
• 3D products with huge polygon counts, advanced
  lighting, texture mapping (such as Quake III
  Arena shown in Figure 10), and all the latest
  whizzy features now jostle for position on the
  shelf, but try to find one of these products that
  uses the 3D technology in an original and
  innovative fashion.  

Fig. 10 Quake III Arena
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DirectX

• Microsoft developed a software development kit
  (SDK) specifically to promote hardware-assisted,
  high-performance games for Windows.
• This SDK, known as DirectX, consists of many
  components, each of which deals with a particular
  aspect of game development.
• Because DirectX is well supported and widely
  known, virtually all 3D games rely on it for the
  features they need.
• The components of DirectX are divided into two
  groups
• DirectX Foundation contains low-level components
  that supply basic functionality
• DirectX Media contains high-level components that
  perform many complex operations.

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DirectX Foundation (1)

• DirectX Foundation consists of the following
  components
• DirectDraw,
• DirectSound,
• DirectMusic,
• Direct3D Immediate Mode (IM),
• Directlnput,
• DirectSetup, and
• AutoPlay.

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DirectX Foundation (2)

• DirectDraw
• DirectDraw provides a way for software developers
  to access the display's attributes - including
  the size of the desktop and how many colors can
  be displayed at once-and the display's features,
  such as playing back video, displaying images and
  bitmaps, and so on.
• DirectDraw is NOT a graphics library, in that it
  cannot draw lines, polygons, or text, but it is
  still nonetheless invaluable for all of today's
  3D games.
• DirectSound
• DirectSound can play, mix, and apply effects to
  sounds on a variety of hardware devices. Many
  programmers rely on DirectSound for all of their
  sound output.
• DirectMusic
• DirectMusic, a recent addition to DirectX,
  supports the playback of MIDI files and other
  kinds of music.

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DirectX Foundation (3)

• Direct3D IM
• Direct3D IM gives programmers direct access to a
  graphics card's 3D features. It is written with
  a minimal amount of code, thus requiring the
  programmer to do most of the work in displaying
  3D environments.
• DirectInput
• DirectInput allows programmers to use existing
  and future input devices. It directly supports
  force-feedback joysticks, normal joysticks, mice,
  flight yokes, and any other input device
  developed with Directlnput support.
• AutoPlay
• AutoPlay allows a CD to start itself after being
  inserted into a CD-ROM drive, thus enabling
  software developers to create self-installing
  games and those that run themselves after being
  inserted.

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DirectX Media (1)

• DirectXMedia consists of only four components
• Direct3D Retained Mode (RM),
• DirectPlay,
• DirectShow, and
• DirectAnimation
• but each one contains a large amount of
  functionality.

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DirectX Media (2)

• Direct3D RM
• Direct3D RM is a high-level component of DirectX.
  Rather than handling only the basics, as IM
  does, RM performs most of the tasks involved in
  displaying 3D scenes. Because it is high level,
  the changes from one version of RM to the next
  tend to be slight, allowing programmers to become
  more familiar with it.
• DirectPlay
• DirectPlay allows programmers to write
  multiplayer software that runs over LANS, modems,
  the Internet, and other networks.
• DirectShow
• DirectShow plays video files of all types -
  QuickTime, AVI, MPEG-according to the filters
  (video decoders) installed on the computer it is
  running on. This provides game developers with
  an easy way to introduce cinematic scenes into
  their games.
• DirectAnimation
• DirectAnimation is a component designed for Web
  and desktop animation.

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The Features Of DirectX

• Today's games use DirectX and so support many if
  not all of the graphical features provided by
  this SDK.
• Polygons
• Lights
• Environmental Effects
• Hardware

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Polygons (1)

• The main primitives simple geometric shape from
  which more complex shapes are formed in 3D games
  is a convex polygon.
• A polygon is a bounded portion of a plane, which
  is, in turn, a shape infinitely wide in two
  dimensions and infinitely flat in the third.
• A convex polygon has no two points through which
  a line can be drawn that passes outside the
  polygon (Fig. 2a). This is contrasted with a
  concave polygon, which has at least two points
  through which a line can be drawn that passes
  outside the polygon (Fig. 2b).

Fig.2 A convex polygon (a) and a concave
polygon (b)
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Polygons (2)

• Nearly all objects in Direct3D games are composed
  of convex polygons.
• Objects with sharp edges, therefore, can be
  replicated exactly, while those with smooth edges
  can be simulated.
• Most games do not display plain, single-color
  polygons. Rather, they display polygons with a
  number of special effects to improve their
  realism.

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Polygons (3)
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Polygons (4)

• Shading
• Direct3D is capable of shading polygons
  realistically to enhance their appearance.
• It can shade polygons based on their positions
  and their orientations relative to one or more
  light sources.
• Gouraud Shading
• Gouraud shading is a fast method of simulating
  curved surfaces.
• The vertices of the polygon are shaded as if the
  polygon were curved, and these resulting shades
  are spread across the face of the polygon.
• This approach does not produce accurate results
  if a highlight from a light falls in the center
  of the polygon (because only the shades at the
  vertices are calculated) but otherwise, it is
  fairly realistic.

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Polygons (5)

• Phong Shading
• Although Phong shading is NOT currently
  implemented in Direct3D, it will be in future
  versions.
• Phong shading is more realistic than Gouraud and
  never misses highlights.
• It shades each pixel of the polygon as if it were
  curved for this reason, it is slower than
  Gouraud shading.
• Texture Mapping
• Virtually all polygons have a texture-an image or
  bitmap-applied to them.
• This image is mapped, or painted, on the polygon.
  
• Usually, each vertex of the polygon is assigned a
  texture coordinates two-dimensional point
  indicating the pixel in the texture corresponding
  to the given polygon vertex.

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Polygons (6)

• Transparency
• Transparency results from giving the texture map
  associated with the polygon a stencil (also
  called a mask) or an alpha channel.
• A stencil allows cutouts portions of the polygon
  can be either fully transparent or fully opaque.
  
• An alpha channel is another component (added to
  the red, green, and blue components of each
  pixel) that specifies to what extent each pixel
  is transparent.
• Alpha channel transparency takes longer to
  compute than stenciling, but is
  hardware-accelerated in all of today's graphics
  cards, and so it is the preferred method of
  transparency.

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Polygons (7)

• Bump Mapping
• Bump mapping refers to the process of modifying
  the appearance of a polygon so it seems bumpy.
• The bumps are specified by an image (sometimes
  called a height or displacement map), and the
  technique is usually used in combination with
  texture mapping.
• Reflection Mapping
• Reflection mapping is a method of simulating
  reflections.
• When a reflection map is applied to a polygon,
  the texture coordinates chosen depend on the
  viewer's location, and the texture map itself is
  an image that resembles the environment.
• This produces the illusion of a reflective
  surface.

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Lights

• Lights play an important role in games, casting
  shadows and illuminating important parts of
  scenes.
• Many games use a combination of real-time
  lighting and pre-rendered lighting.
• Real-time lighting is calculated while the game
  is playing - all the mathematics for generating
  shadows and other lighting effects is done by the
  game every time the 3D world is displayed.
• Pre-rendered lighting is calculated in advance by
  a 3D modeling program and applied to objects in
  the game world (this lighting type is faster, but
  cannot be used for moving lights).

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Environmental Effects (1)

• In addition to the many effects applied to
  polygons, Direct3D supports environmental effects
  - those that are global and affect all objects in
  the game world.
• Fog
• Fog is a generic name for any type of color that
  distant objects converge to.
• It can be white to simulate real fog, black to
  simulate nighttime, or another color.

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Environmental Effects (2)

• Shadows
• Today's games increasingly make use of shadows,
  which Direct3D supports.
• Game designers usually decide that not all
  objects should have shadows - only select objects
  (like characters and moving vehicles, for
  example), because using shadows for all objects
  within a 3D world is computationally expensive.
• Many objects, because they do not move, can be
  given textures with pre-drawn shadows,
  eliminating the computational cost at the expense
  of memory.
• Another technique involves modifying the
  intensities of the polygon's vertices (similar to
  Gouraud shading), making those that lie within
  shadow regions darker and those that do not,
  lighter. This technique crudely approximates
  real shadows, but is fast and universally
  supported by hardware.

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Summary

• The first step in becoming a three-dimensional
  game programmer is to understand what elements
  contribute to the graphics of three-dimensional
  games.
• For Windows programmers, those elements are
  usually the features supplied by Microsofts
  DirectX, a high-performance COM SDK aimed
  specifically at the game-developer community.
• DirectX gives developers direct control over
  graphics accelerators, input devices, sound
  cards, and more.
• Credit goes to the manufacturers of graphics
  accelerators for the radical new advances in the
  quality and performance of three-dimensional
  games.
• These graphics accelerators natively support a
  growing list of 3D features, enabling developers
  to produce games that are richly detailed and run
  at high speeds.