A presentation on
DirectX®
Alex Brill
Emil Elazar
Noam Monheit
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Contents
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What is DirectX?
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How DirectX really works?
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Historical Problem and it’s Solution
Terminology
Brief Components Description
DirectX Versions History
Architecture
Direct3D in Details
DirectX Alternatives
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OpenGL
Advantages & Disadvantages or: “Why DirectX”?
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Installation + SDK
 Demo + Code Examples
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What is DirectX? (1)
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The Problem:
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Dos vs. Windows 3.1 overhead.
The PC architecture was never designed as a gaming
platform.
Machine can be VERY different from another.
The will:
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Windows a desirable platform for game development.
Fast, low-level libraries to allow the developer maintain
creative freedom over his games.
Shift the burden of hardware support from the game
developer to the hardware manufacture.
Coexist peacefully with other Windows components.
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What is DirectX? (2)
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The Solution: DirectX
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Direct access to Hardware…
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A common standard which all games and multimedia
applications could follow – a common interface with
whatever hardware is installed in the PC.
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Provides real-time multimedia and gaming services to
programs: graphics, sound, music, input (mouse /
keyboard / joystick / etc), networking, and movie playback.

Done by three Microsoft employees—Craig Eisler, Alex St.
John, and Eric Engstrom.
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What’s DirectX? (3)
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There are two parts to DirectX; the 'runtime' and the 'SDK'
(Software Development Kit). Both are free; the runtime is what
players need to have on their computers in order to play a game,
and the SDK is what a programmer needs to create games that
use DirectX.
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Windows XP comes with the DirectX 8 runtime automatically
installed; it's a 4 MB download if players don't have it.
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The SDK, is over 100 MB to download, and it contains all the
headers and libraries you need, plus documentation, samples,
tutorials, and tools. Players don't need the SDK, only the runtime.
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Most games for Windows nowadays use DirectX in some form or
another; it is also the technology which powers Microsoft's XBox.
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What is DirectX? (4)
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Terminology (1)
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API (application program interface)- Set of routines,
protocols, and tools for building software applications.
Saves the programmer from dealing with
implementation.

Driver- Program that controls a device. Acts like a
translator between the device and programs that use
the device.
Each device has its own set of specialized commands
that only its driver knows. In contrast, most programs
access devices by using generic commands. The
driver, therefore, accepts generic commands from a
program and then translates them into specialized
commands for the device.
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Terminology (2)
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Sound Card- Enables the computer to output sound
through speakers connected to the board, record
sound input from a microphone connected to the
computer, and manipulate sound stored on a disk.
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Video Adapter- A board that plugs into a PC to give
it display capabilities.
Modern video adapters contain memory, so that the
computer's RAM is not used for storing displays. In
addition, most adapters have their own graphics
coprocessor for performing graphics calculations.
These adapters are often called graphics
accelerators.
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Terminology (3)
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Graphics Accelerator- Type of video adapter that contains its
own processor to boost performance levels.
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These processors are specialized for computing graphical
transformations, so they achieve better results than the general-purpose
CPU used by the computer.
In addition, they free up the computer's CPU to execute other commands
while the graphics accelerator is handling graphics computations.
Other characteristics that differentiate graphics accelerators:
 memory : Amount of memory determines resolution and colors amount.
Two types of memory-DRAM or video RAM (VRAM), which enables the
video circuitry and the processor simultaneously access the memory.
 bus : 1995: PCI bus, nowadays; PCIExpress bus.
 register width: The wider the register, the more data the processor can
manipulate with each instruction. 64-bit accelerators are already
becoming common, and we can expect 128-bit accelerators in the near
future.
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Terminology (4)
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GDI- Graphical Device Interface, a
Windows standard for representing
graphical objects and transmitting them
to output devices, such as monitors and
printers.
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HEL, HAL, COM and more to be
discussed later…
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DirectX Components
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DirectX Graphics
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DirectInput
DirectPlay
DirectAudio
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DirectDraw
Direct3D
DirectSound
DirectMusic
DirectShow
DirectSetup
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DirectX Components (1)
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DirectX Graphics
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DirectDraw- A software interface that provides direct access to display
devices while maintaining compatibility with the GDI and for transferring
video processing from a PC's CPU to the video adapter.
The standard was first developed by Intel and called the Display Control
Interface (DCI) and later supported by Microsoft.
When the CPU is not busy, the GDI updates the video display. If the CPU is
busy, the DCI driver allows an application to send update information
directly to the video adapter.
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Direct3D- An API for manipulating and displaying three-dimensional
objects. Developed by Microsoft, Direct3D provides programmers with a
way to develop 3-D programs that can use whatever graphics acceleration
device is installed in the machine. Virtually all 3-D accelerator cards for PCs
support Direct3D.
Another 3-D standard offering similar functionality is OpenGL.
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DirectX Components (2)
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DirectInput- Enables an application to retrieve data
from input devices even when the application is in the
background.
Also provides full support for any type of input device,
as well as for force feedback.
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DirectPlay- A media-independent networking API that
provides networking services at the transport protocol
and session protocol levels. DirectPlay sessions can
be run on TCP/IP networks, IPX networks, and over
directly connected modems and serial cables.
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DirectX Components (3)
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DirectX Audio
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DirectSound- Enables the playing of
sounds with very low latency and gives
applications a high level of control over
hardware resources.
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DirectMusic- In combination with
DirectSound, DirectMusic provides a
complete solution for playing music and
sound effects in games and other
applications.
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DirectX Components (4)
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DirectShow- An architecture for streaming
media on a Windows platform. It provides
high-quality capture and playback of
multimedia streams. Screeen Saver, Camera..
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DirectSetup- Extremely simple library of
functions for installing DirectX on a machine.
It also provides a way to check the version of
DirectX that is present.
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Versions (1)
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For each new version of DirectX, Microsoft
updated the technology such that the new dll's
can communicate with the hardware faster and
more efficiently with minimum latency.
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They’re trying to support the latest features of
graphics and sound cards that come on the
market.
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The architecture is updated so as to suit the
needs of the day while maintaining backward
compatibility.
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Versions (2)
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DirectX 1.0
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DirectX 6
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2 independent SDK's (DirectX SDK and DirectX Media SDK).
DirectX 7
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released on late 1995.
DirectShow- the significant part of Media SDK, merged into
the DirectX API and DirectX Media deprecated.
DirectX 8
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DirectDraw and Direct3D merged into a single DirectX
Graphics API for graphics programming.
DirectSound and Direct Music merged together as DirectX
Audio for sound programming.
Programmable Pixel Shader and Vertex Shader introduced.
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Versions (3)
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DirectX 9
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HLSL (High Level Shader Language), a powerful new
programming model that offers the easiest to use graphics
creation toolset for developers introduced.
DirectX10– Part of Windows Vista.
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No backward compatibly except via a software layer.
Much faster DLL’s
Departure from driver model of DirectX 9.0, with the addition
of a scheduler and memory virtualization system.
DirectX 10 will forego the current DirectX practice of using
"capability bits" to indicate which features are active on the
current hardware. Instead, DirectX 10 will define a minimum
standard of hardware capabilities which must be supported for
a display system to be "DirectX 10 compatible".
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Versions (4)
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Which version of DirectX do various versions of
Windows come with?
95
95B
NT
NT w/SP 4
98
98SE
ME
2000
XP
None
DX 3(Supports up to DX8)
DX2
DX3
DX5
DX6
DX7.1
DX7.1
DX8.1
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Screenshots
Wolfenstein (3D Realms 1992 –> no HAL):
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DirectX in details
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DirectX – COM objects
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DirectX is a set of APIs, available as COM objects.
Component Object Model (COM) is a Microsoft
platform for software componentry introduced by
Microsoft in 1993. It is used to enable crossapplication communication and dynamic object
creation in any programming language that supports
the technology.
All DirectX Interfaces inherit from IUnknown and are
COM compliant.
IUnKnown:
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AddRef()
Release()
QueryInterface()
Reference counting
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Backward Compatibility (1)
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COM allows Microsoft release an enhanced set of
DirectX components that are completely compatible
with earlier versions of DirectX.
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With COM’s independence of a programming
language, developers are free to choose whatever
COM compliant language and development
environment they wish.
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With COM’s programming model, the programmer is
assured that even if the user upgrades or changes
hardware configuration and DirectX drivers, the
software will work without reconfiguration.
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Backward Compatibility (2)
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For example, even though DirectDraw was erased
from the DirectX API components after DirectX 7
even in DirectX9, you can access the old interfaces
through a DirectDraw7 call.
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This backward compatibility plays a significant role
in DirectX's position as a leading API, as it helps the
applications written in older versions to still work
smoothly in the newer versions.
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How it really works?
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DirectX provides the interface to access the
advanced features of the display adapter,
which are not provided in the standard
Windows GDI graphics interface.
 It accesses the hardware abstraction layer in
Windows directly.
 When DirectX was introduced, display adapter
vendors were quick to develop DirectX drivers
that would expose low-level functions of
their hardware to the application.
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Architecture
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Each chip manufacturer, board producer, or OEM implements a
HAL which implements only device-dependent code and performs
no emulation.
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The HAL is implemented using 32-bit code with Microsoft
Windows XP, Microsoft Windows NT, and Windows 2000.
Windows 98 and Windows Millennium Edition (Windows Me) use
a combination of 16-bit and 32-bit code.
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The HAL can be part of the display driver or a separate dynamiclink library (DLL) that communicates with the display driver
through a private interface that the driver's creator defines.
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HAL is based around the hardware support, and is very fast but
might not support everything
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Architecture
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When DirectX is initialized, it checks the hardware to
see if the hardware supports certain capabilities. If the
hardware does support a certain capability, then the
HAL will be used to access that hardware function;
otherwise, the HEL will be used to emulate the
capability through software.
HEL bypasses the hardware and implements its own
functionality.
HEL uses no hardware acceleration. It uses the CPU,
software, and normal system RAM. It is usually MUCH
slower, but much less problematic
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Architecture
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3D - Graphics
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Rendering - the process of generating
an image from a model, by means of a
software program .
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3D - Graphics
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The Application is your game and is where you do any
scene management and any tessellation of mesh etc.
You then feed the graphics card with vertices and
other data.
The graphic card processes the vertices by
transforming and lighting them using the matrices
supplied by the application.
The card then culls any invisible polygons and clips to
the viewport.
This transformed data is then rasterized and passes
through the pixel operations
The data is displayed .
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3D - Graphics
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Some terms…
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Rasterisation - The task of taking a twodimensional image described in a vector
format and converting it into pixels or dots for
output on a video display or printer.
 A tessellation (tiling) of
the plane is a collection
of plane figures that fill the
plane with no overlaps and no gaps.
 A shader is a program used to determine the
final surface properties of an object or image.
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Programmable Pipeline
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One of the most important new features in
DirectX Graphics is the addition of a
programmable pipeline.
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It provides an assembly language interface to the transformation and
lighting hardware (vertex shader) and the pixel pipeline (pixel shader).
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This programmable pipeline gives the developer a lot more freedom to
do things, which have never been seen in real time applications before.
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The shader code is loaded into the graphics card memory and plugged
directly into the graphics pipeline. Shader code is in assembly however
nowadays there are a number of higher level 'C' type languages that can
be compiled down to the assembly and making them much easier to
program.
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Microsoft have HLSL (High-Level Shading Language) for use with
DirectX and OpenGL has the GLSL (OpenGL Shading Language).
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Programmable Pipeline
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When you push vertices through the pipeline, they need
to be transformed and lit.
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This processing stage is known as T&L.
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Hardware vertex processing means this is done in
hardware, if hardware supports it;
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Software vertex processing is done in software.
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The general practice is to try creating a Hardware T&L
device. If that fails try Mixed, and if that fails try Software.
(If software fails, give up and exit with an error).
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DirectX - Conclusion
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DirectX gives multimedia applications greater access
to advanced features of high-performance hardware
such as 3D graphics acceleration chips and sound
cards.
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It controls 2D graphics acceleration;
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Support for input devices: joysticks / joy-pads,
keyboards, mice, controls sound mixing and sound
output on a vast range of audio
hardware, controls networking and multiplayer gaming,
and control over various multimedia streaming
formats.
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DirectX Alternative (1)
Open Graphics Library is a
specification defining a
cross-language crossplatform API for writing applications that
produce 3D computer graphics (2D
computer graphics as well). The interface
consists of over 250 different function calls
which can be used to draw complex threedimensional scenes from simple primitives.
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DirectX Alternative (2)
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The OpenGL specification is overseen
by the OpenGL Architecture Review
Board (ARB), which was formed in
1992. The ARB consists of a set of
companies with a vested interest in
creating a consistent and widely
available API.
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DirectX Alternative (3)
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OpenGL- platform Independent; supported on
Windows, Mac, Linux, and several other UNIX
variants.
Direct3D- only Windows.
OpenGL- function oriented interface.
Direct3D- object oriented interface.
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DirectX Alternative (4)
Direct3D- updated very frequently (once
a year) and supports the latest card
features (Microsoft).
 OpenGL- takes some time to reach a new
standard (open-standard and a
community product, Silicon Graphics).
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Performance : Equal performance!!
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Where do I start?
If you're worried about which one to
learn, and which one the pros use, the
answer is that more often than not they'll
use both.
 Apart from Direct3D, all the DirectX
components can be used alongside
OpenGL. If you want to use DirectInput
for joystick input and OpenGL for your
graphics, that's fine.

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Games(1)
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The 3D engine of the
game Battlefield 1942
sits solidly on a
DirectX 7 foundation.
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Games(2)
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Unreal Tournament
2003 uses a number of
DirectX 8 shader
effects. As a result, the
game's graphics look
much better than that
of older games, and
the in-game world
seems more alive.
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Games(3)
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FarCry can be
considered the first
game that makes
consistent use of
shaders. Thanks to
DirectX 9, the surfaces
look very realistic and
react to changes in
lighting.
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Further Reading - Web Resources
General

International Game Developers Assoc. - www.igda.org
 GamaSutra - www.gamasutra.com
 Game Developer - www.gamedev.net
Direct X

MSDN - www.msdn.com/directx
 Newsgroup microsoft.public.win32.programmer.directx.managed
 The Z Buffer - www.thezbuffer.com
 Tom Miller (main coder/designer) - blogs.msdn.com/tmiller
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Further Reading - DirectX Books
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The End
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