3D Graphics Hardware: Topics

1
3D Graphics Hardware Topics

• Rationale
• Processing model
• Memory handling
• Resolution X, Y, colour depth
• Buffering
• Textures, compression, filtering
• Antialiasing
• Hardware Transform and Lighting (TL)

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The Need for Speed

• Houses are never big enough, disc drives are
  always full, desks always run out of room we
  humans will expand into any available space
• As computer systems get faster, we use them in a
  more demanding way, we expect more next time
• There are a number of hard problems that we need
  much more power to solve

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Processor-intensive problems

• Continuous-speech recognition
• Natural handwriting recognition
• General artificial intelligence
• Real-time video encoding and decoding
• High-fidelity virtual environment simulation
• Protein-folding modelling and simulation
• Weather modelling and simulation
• and many more

4
The High Cost of Realism

• We take our 3D environment for granted
• Simulating a 3D environment on a 2D screen seems
  simple but turns out to be rather hard to do
• The human eye is an exquisitely sensitive
  instrument with many non-obvious properties

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The High Cost of Realism

• We need more than 20 video frames per second to
  fool the eye into seeing motion
• Movies very high resolution but only 24fps
• PAL TV low resolution and 25fps
• NTSC TV even lower resolution but 30fps

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The High Cost of Realism

• We need at least 16-bit colour and 800 by 600
  pixels, with antialiasing, for a basic scene
• 2 bytes per pixel (3 or 4 is better)
• 800600 pixels of output data (1600 by 1200 is
  nice)
• more than 20 times a second (50 is better)
• This leads to a bare minimum of over 18 Megabytes
  of processed output data per second
• Over 360MB/sec for the preferred resolution

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The High Cost of Realism

• If we have a top-end 40-inch TV with 3840 by 2400
  resolution
• 4 bytes per pixel
• 38402400 pixels of output data
• 60 times a second
• This leads to a bare minimum of over two
  Gigabytes of processed output data per second,
• and over 35MB per frame

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The High Cost of Realism

• How much extra data gets processed behind the
  scenes?
• What about the perspective and distortion
  calculations?
• How do texturing, lighting, smoothing and
  reflections get processed?
• 3D is a tough problem solutions combine
  specialised hardware, special bus architectures,
  fast memory and heavily optimised software

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Simplified Processing Model

• The graphics card needs copies of all the texture
  bitmaps that are going to be used for the frame
• All of the objects to be drawn must be sent to
  the graphics card in some format
• Each item to be drawn has a position in space,
  surface properties (e.g. multiple textures to
  apply) and an orientation

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Simplified Processing Model

• Items are either invisible, visible or partly
  visible (viewport-clipped or obscured by other
  objects)
• If visible, the object is rendered to the screen
• Different video cards implement this simplified
  model in various ways, but many parts are common
  to all video cards

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Memory handling

• Unified memory architecture (UMA) helps make
  GPUs more flexible and can help reduce costs by
  using memory efficiently
• Early 3D cards (e.g. 3Dfx Voodoo one) had texture
  memory and video buffer memory as separate units,
  physically different RAM chips
• With UMA, higher resolutions can be traded off
  against less texture capability

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Resolution x, y, bit-depth

• The frame buffer is what a video board uses to
  store the images it renders
• The amount of frame buffer memory a video board
  has directly impacts which resolutions it can
  support
• The more memory you've got, the higher
  resolutions the board will support, and at higher
  bit depths.

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Resolution x, y, bit-depth

• Most cards support 16-bit colour (usually 565
  format) and 24-bit colour (RGB 888)
• 32-bit colour is 24-bit colour plus 8-bit
  transparency/blending (RGBT)
• Video (frame buffer) memory requirements may be
  calculated by considering WidthHeightcolour
  depth
• Pixel Width Pixel Height gives total number if
  pixels in the frame

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Resolution x, y, bit-depth

• Colour depth tells us how many bytes of storage
  are required per pixel
• 1 byte for 256 colours (usually simple 2D
  graphics modes)
• 2 for 64K colours bad for subtle gradients
  (e.g. the sky)
• 3 for 16M colours so-called true colour
• 4 for 16M colours plus transparency channel
• Thus 12801024, true colour uses 3.75MB of video
  memory for each display buffer
• For animation we need two frame buffers (? 7.5MB)

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Buffering

• Most 3D graphics systems use two or three frame
  buffers, drawing to one whilst displaying another
• Textures are buffered (cached) in video memory
• Object meshes (triangle data) must be stored
  temporarily when objects are on screen
• 3D game objects are built from lots of triangles
• In a H/W TL (Texturing and Lighting) card, there
  must be a large object buffer too

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Buffering and memory trends

• 1997 4MB of video ram was standard
• 1998 8MB
• 1999 16MB 32MB
• 2000 32MB 64MB (high speed memory)
• 2002 64MB 128MB (very high speed memory)
• 2004 128MB 256MB
• 2006 128MB 512MB (ridiculously fast GRAM)
• 2007 128MB 1GB
• 2015 8GB 16GB predicted

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Monitor and Display trends

• Mid 1980s 640 by 480, 16 colours
• Early 90s 640 by 480, 256 colours
• Late 90s 800 by 600, 256 colours
• 2000 1024 by 768, 256 colours
• 2003 1024 by 768, 64K colours
• 2005 1280 by 1024, 16M colours
• 2006 - 2007 gt30 TV, 3840 by 2400, 16M
• 2015 7680 by 4320 planned

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Conclusion

• Graphics cards do a very hard job
• Graphics resolution is climbing fast
• Buffer size is also increasing very quickly
• The job isnt getting any easier
• Capabilities double every two years or less