Graphics Pipeline

1
Fac. of Comp., Eng. Tech. Staffordshire
University
3D Computer Graphics
Graphics Pipeline
Dr. Claude C. Chibelushi
2
Outline

• Introduction
• Typical Pipelines
• Gouraud shading
• Phong shading
• Ray tracing
• Graphics API Pipeline
• Rendering Hardware
• Performance requirements
• Acceleration methods
• Sample architecture PlayStation 2
• Summary

3
Introduction

• Graphics pipeline
• sequence of processes for generating 2D display
  of 3D scene
• processes can be implemented in hardware or
  software
• main processes
• geometric transformations
• e.g. translations, rotations, projection (see
  viewing pipeline)
• application of shading to visible surfaces

4
Introduction

• Processing sequence for 3D graphics
• primarily dictated by efficiency considerations
• minimisation of amount of computations and number
  of polygons processed
• discard invisible elements from pipeline as early
  as possible
• culling (object / back faces), polygon clipping
• display at appropriate level of detail
• polygonal simplification applied to far objects
• no single pipeline is efficient for all
  applications
• designer should find right (combination /
  sequence of) techniques for optimum performance

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Typical Graphics Pipelines
Material processing colour, texture,
transparency,
Geometry models
Viewpoint
Viewport
Lights materials

• Shapes
• World pos., orient., sizes

• Pos., orient.
• Field of view
• Projection type

• Pos., orient. of display area

• Light pos., orient.
• Optical char.

Typical graphics pipeline
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Typical Graphics Pipelines

• Gouraud- or Phong-shaded polygonal worlds
• 1. Model loading / generation
• loading / generation of graphics primitives
  (lines, polygons, ), and context information
  (colour, transformation matrices, surface
  normals, )
• 2. Modelling transformation
• graphics primitives (and possibly surface
  normals) transformed from object coordinates to
  world coordinates

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Typical Graphics Pipelines

• Gouraud- or Phong-shaded polygonal worlds (ctd.)
• 3. Trivial accept/reject classification
• back-face culling
• accept/reject test
• accept (reject) primitives that lie wholly inside
  (outside) view volume
• mark (for clipping) all primitives neither
  accepted nor rejected (i.e. intersect view volume
  boundary)

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Typical Graphics Pipelines

• Gouraud- or Phong-shaded polygonal worlds (ctd.)
• 4. Vertex or pixel lighting
• apply illumination model (ambient / diffuse /
  specular) to polygon vertices or pixels
• model applied once per vertex (Gouraud shading)
• model applied once per pixel (Phong shading)
• hence (for Phong shading) illumination model best
  applied during scan conversion (see 9)

9
Typical Graphics Pipelines

• Gouraud- or Phong-shaded polygonal worlds (ctd.)
• 5. Viewing transformation
• world coordinates transformed into viewing
  coordinates
• 6. Clipping
• primitives marked in step (3) clipped to view
  volume

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Typical Graphics Pipelines

• Gouraud- or Phong-shaded polygonal worlds (ctd.)
• 7. Projection
• 3D viewing coordinates transformed into 2D
  coordinates
• 8. Viewport transformation
• projected coordinates transformed into device
  coordinates
• 9. Rasterisation includes
• scan conversion, pixel-based hidden-surface
  removal, and shading (and sometimes, mapping
  surface details texture, bumps, )

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Typical Graphics Pipelines
3D Models
Possible 3D graphics pipeline (z-buffer algorithm
and Gouraud shading)
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Typical Graphics Pipelines
3D Models
Possible 3D graphics pipeline (z-buffer algorithm
and Phong shading)
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Typical Graphics Pipelines
3D Models
Possible 3D graphics pipeline (BSP algorithm and
Phong shading)
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Typical Graphics Pipelines
3D Models
Possible 3D graphics pipeline (ray tracing)
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Graphics API Pipeline

• DirectX 8
• graphics pipeline

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Graphics API Pipeline

• DirectX 9 graphics pipeline

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Rendering Hardware

• Layered architecture of graphics system

DirectX Graphics
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Rendering Hardware

• Performance requirements
• 3D computer graphics requires substantial
  computational power and high bandwidth
• computation
• geometric manipulations (vertex transformations,
  polygon clipping) and illumination
• typically require floating-point calculations
• rasterisation requires colour / coordinate
  interpolation, depth testing
• can use integer or fixed-point calculations

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Rendering Hardware

• Performance requirements
• data transfer rate (bandwidth)
• rasterisation requires memory access for depth
  testing, and clearing buffers between frames
• display requires memory (frame buffer) access and
  data transfer to VDU
• Mapping of surface characteristics (bumps,
  textures, ...) increases requirements

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Rendering Hardware

• Acceleration methods
• Computational throughput increased through
• concurrent execution (pipelining or parallel
  processing) of rendering processes
• Bandwidth increased through use of
• special memory devices dual-ported video RAM
  (VRAM), synchronous DRAM (SDRAM),
• high-bandwidth data paths (e.g. Intels
  Accelerated Graphics Port (AGP))

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Rendering Hardware

• Acceleration methods
• Pipelining sequentially-connected multiple
  modules perform tasks concurrently, e.g.
• stages of graphics pipeline can run concurrently
  
• e.g. clipping and lighting vertices of current
  polygon while previous polygon is undergoing
  rasterisation

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Rendering Hardware

• Acceleration methods
• Parallel processing independent multiple modules
  perform task(s) in parallel, e.g.
• matrix multiplication
• simultaneous calculation of row-to-column
  sum-of-products
• rasterisation
• colour and occlusion information for each pixel
  computed independently from other pixels of same
  polygon

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Rendering Hardware

• Illustrative architecture

Pixel processor
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Rendering Hardware

• Sample architecture PlayStation2

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Rendering Hardware

• Sample architecture PlayStation2

(sources Oka 1999, Froggatt 2002)
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Rendering Hardware

• Sample architecture PlayStation2 (Emotion Engine)

(source Kunimatsu 2000)
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Rendering Hardware

• Sample architecture PlayStation2 (Emotion
  Engine)
• Legend
• COP Co-processor
• DMAC DMA Controller
• EFU Elementary Function Unit
• GIF Graphics synthesiser Interface Unit
• VIF Vector Interface Unit
• V(P)U Vector (Processor) Unit

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Rendering Hardware

• (source Macedonia 2000)

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Rendering Hardware

• Supported features
• Range of features typically supported
• illumination and shading, z-buffering
• alpha blending (transparency)
• mapping of surface characteristics (2D / 3D
  textures, bumps, ...), antialiasing
• tesselation or direct processing of curved
  primitives
• stereo display, ...

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Suggested Reading

• Relevant parts of Ch. 10 15, A. LaMothe, Black
  Art of 3D Game Programming, Waite Group Press,
  1995.
• Relevant parts of Ch. 7, 16, 18, J.D. Foley, A.
  Van Dam, et al., Computer Graphics Principles
  and Practice, 2nd Ed. in C, Addison-Wesley, 1996.
• Z. Soferman, D. Blythe, N.W. John, Advanced
  Graphics Behind Medical Virtual Reality
  Evolution of Algorithms, Hardware, and Software
  Interfaces, Proc. of the IEEE, Vol. 86, No. 3,
  pp. 531 - 554, 1998.

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Suggested Reading

• M. Froggatt, The Power to Play, IEE Review, Vol.
  48, No. 2, pp. 13 - 19, 2002
• A. Kunimatsu et al., Vector Unit Architecture for
  Emotion Synthesis, IEEE Micro, Vol. 20, No. 2,
  pp. 40 - 47, 2000
• M. Oka, M. Suzuoki, Designing and Programming the
  Emotion Engine, IEEE Micro, Vol. 19, No. 6, pp.
  20 - 28, 1999
• M. Macedonia, The Empire Strikes Back... with the
  X-Box, IEEE Computer, Vol. 33, No. 6, pp. 104 -
  106, 2000.

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Summary

• Graphics pipeline processing sequence that
  results in 2D display of synthetic 3D scene
• main components
• geometry sub-system transformations, clipping,
• rasterisation sub-system scan conversion,
  hidden-surface removal, shading, detail mapping
• No single pipeline is best for all applications
• configuration dictated by
• requirements of application, and mix of techniques

33
Summary

• 3D computer graphics carries substantial
  computational and bandwidth costs
• hardware acceleration through
• pipelining or parallel processing
• special memory devices and high-bandwidth data
  paths
• wide variety of rendering hardware