Computer Graphics Introducing DirectX

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Computer GraphicsIntroducing DirectX

• CO2409 Computer Graphics
• Week 5-2

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Todays Lecture

• Terminology
• A History
• DirectX Components
• DirectX Graphics
• Rendering Pipeline
• Using DirectX
• Future Directions

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Terminology

• DirectX is an SDK
• Software Development Kit
• Set of software tools, APIs and documentation to
  enable development of specialist software
• DirectX contains a set of APIs
• Application Program Interfaces
• An API is a definition of how to interface with
  (i.e. use) some other software or device
• For DirectX the other software is the DirectX
  core and hardware drivers
• These APIs take the form of libraries of
  functions and types that can be used in C, C
  etc.
• The TL-Engine is also used through an API

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DirectX A History

• Conceived in 1994
• Targeted at games developers who preferred DOS
  over the newer Windows operating system
• Intended to provide low-level access to system
  resources within a high-level OS
• First few iterations were fairly unusable
• However, by DirectX 5 provided a reasonable
  development platform
• Later versions have been developed in close
  collaboration with hardware vendors
• Currently on DirectX 9.0c for Windows XP
• DirectX 10 is available only on Windows Vista.

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DirectX Components

• DirectX contains three major components
• DirectX Graphics (or Direct3D)
• 2D and 3D graphics
• Low level control and higher level helper
  utilities
• DirectX Input
• For keyboard, mouse, joystick other input
  devices.
• DirectX Sound
• Capture and playback of sound effects
• One API for each of these components

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Previous Components

• DirectX is generally backwards compatible with
  all previous versions
• Older components that have since been deprecated
  are still usable, e.g.
• DirectDraw 2D drawing, superseded
• DirectPlay Network gaming, deprecated
• DirectShow Video playback, superseded
• DirectMusic Music playback - in limbo
• These components should be avoided
• Ensure you read the latest documentation
• Avoid website tutorials for older versions

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DirectX Graphics

• Will use DirectX Graphics in this module
• The SDK provides
• An API a set of functions and classes
• We will use this extensively (in C)
• Full documentation, tutorials and samples
• Very useful reference
• Development Tools, mainly regarding pixel, vertex
  geometry shaders
• We will see a little of these
• The SDK is on the games lab machines

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DirectX Graphics Pipeline

• All the DirectX Graphics features can be
  illustrated as a pipeline of operations
• From initial geometry to final pixel rendering

Reproduced from the SDK documentation
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Pipeline Input Data

• The pipeline starts with vertex and primitive
  data
• Have seen vertices, primitive data is mainly
  polygons
• This is the 3D geometry that we have discussed
  already
• The tessellation stage allows for automatic
  refinement of the original geometry
• Rarely used

This geometry data is in the form of triangle
strips an important method of storage for 3D
graphics APIs
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Pipeline Vertex Processing

• Vertex Processing describes transformations
  applied to the 3D geometry to
• Position and orient elements
• Blend geometry for animation
• Create special effects
• E.g. deformation
• But the most important step is to create the 2D
  view of the 3D geometry
• as seen from a particular point

Transformation from 3D to 2D geometry
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Pipeline Lighting

• The vertex processing stage can also calculate
  lighting
• Three main kinds of lights
• Directional lights
• Point lights
• Spot lights
• The effects are calculated with some simple
  vector mathematics
• Note that shadows are dealt with separately from
  lights

Light Types
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Geometry Pixel Processing

• These stages describe the conversion of the
  transformed 2D geometry into pixels
• This covers many topics
• Clipping, culling, depth buffers
• Textures, bump mapping environment mapping etc.
• Special effects
• Advanced lighting techniques
• Depth of field
• Etc. etc

Special per-pixel effects in Half Life 2
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Pixel Rendering

• Final blending of the pixels onto the viewport
• Have seen some of the possibilities here when
  working with sprites
• E.g. Additive, multiplicative, alpha blending
• Will cover each pipeline stages using DirectX
• Stages are similar for other graphics libraries

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Beyond the Basic Pipeline

• This describes the basic fixed pipeline
• Parts of the pipeline are now programmable
• Vertex, geometry and pixel shaders
• More flexibility in how processing is performed
• Will look at fixed pipeline first to introduce
  concepts
• But quickly move on to the use of shaders
• Standard development technique nowadays
• Advanced topics move beyond basic pipeline
• E.g. shadows, animation

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Using DirectX

• First initialise a Windows application and
  prepare DirectX
• This stage is fairly standard for all DX
  applications
• Prepare some 3D geometry to render
• We will look at these two stages in initial labs
• Then use the DirectX API to program the stages in
  the graphics pipeline
• Will use a some helper functions to do this
• A subset of DX Graphics called the D3DX library
• Designed to be easier to use than the core API

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DirectX 10

• DirectX 10 is a major update, compatible only
  with Windows Vista
• Key changes
• Refined architecture to suit Vista
• Vistas GUI now DirectX driven
• Requires minimum specification for hardware
• Less need for fall-back techniques on weaker
  hardware
• Adds geometry shaders
• Manipulate/generate triangles in a shader
• Shaders can write back to GPU memory
• Shaders can dynamically update geometry
• Reduce CPU work, e.g. particle system entirely on
  GPU