GRPHICS01 - Introduction to 3D Graphics


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This is a course on the theoretical underpinnings of 3D Graphics in computing, suitable for students with a suitable grounding in technical computing.

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GRPHICS01 - Introduction to 3D Graphics

  1. 1. INTRODUCTION TO 3D Michael Heron
  2. 2. INTRODUCTION  For the next three weeks we will be talking about 3D graphics.  Specifically, 3D graphics using the open source blender package.  Module will concentrate on technical content.  I have absolutely no artistic skill in the slightest.  Seriously.  Content time broken up into:  Two lectures  One tutorial  One lab prep  Four hour lab slot
  3. 3. GRAPHICS  Graphical images on a computer monitor are made up of 2D arrays of pixels.  The number of pixels in that array is dependant on the system’s resolution.  Pixels represent a single element of an image.  Represented by a colour code.  Pixels have a depth.  Represents the expressive palette of colours.  8 bit depth represents 256 colours  24 bit represents 16.8 million colours
  4. 4. COLOUR REPRESENTATION  Colours are usually represented by an RGB value.  An array of three digits corresponding to the blend of colours.  An RGB value of {0,0,0} represents white.  An RGB value of {255,255,255} represents black.  Other colours made up of points in-between.
  5. 5. 4-BIT COLOUR
  6. 6. 8-BIT COLOUR PALETTE © Lucasarts, 1990
  7. 7. 24-BIT COLOUR PALETTE © Lucasarts, 2009
  8. 8. DISPLAYING GRAPHICAL INFORMATION  Graphics are displayed on a computer monitor using rasters.  Lines of pixels.  CRT monitors make use of electron guns to display images on the screen.  Three guns (red, green, blue)  Guns fire beams at the phosphor coating on the inside of the monitor.  This occurs many times per second.  Governed by the monitor’s refresh rate.
  9. 9. DISPLAYING GRAPHICAL INFORMATION  An LCD works somewhat differently.  A backlight is used to create light  This light passes through two substrates of polarised glass.  While this is happening, an electrical current causes the crystals within the substrates to align.  The combination of these substrates allows for the desired colours to appear at the appropriate point.  There are other ways too  Not important at this time.
  10. 10. REPRESENTING GRAPHICS (2D)  Two main way of representing graphics in a computer.  Rasters, comprised of arrays of pixels.  Vectors, comprised of collections of objects expressed as mathematical formulae.  Rasters used to represent photographs and other such bitmaps.  Vectors used to represent more asbtract models.
  11. 11. REPRESENTING GRAPHICS (3D)  In three dimensions, vectors are used almost exclusively for representing shapes.  Images built up of collections of vertices, points, and polygons.
  12. 12. DIFFERENCES IN REPRESENTATION  2D Images  Raster  Permits great amounts of detail but no representation of relationship between objects.  Substantial file size  Vector  Permits relationship of objects.  Minimal details permitted  Difficult to represent details using basic shapes  Several trade offs  Processing Power  Realism  Modifiability  Expressive Potential.
  13. 13. 3D GRAPHICS  Complex 3D scenes can be created as 2D images.  Often done using ray-tracing or other technologies.  Not real-time  Goal of 3D graphics is to permit photorealistic representations of complex spatial topographies.  Difficult task  Requires much investment in building environments and objects within them  Many applications require real-time rendering.  Games
  14. 14. PHOTOREALISM  3D Graphics seeks to achieve photrealism by:  Vector representation of 3D Objects  Texturing of 3D objects in materials  Interaction of light on objects  Shadows  Reflections  Colour  Glare  Photorealism is important for many contexts.  Simulation, entertainment, research, medical teaching
  15. 15. 3D ON A COMPUTER  Not possible to show 3D images on a computer.  Monitor is an inherently 2D device.  Techniques are used to simulate the appearance of three dimensions.  Use of perspective, layering, projection of a plane onto a fixed view.  Many different interacting parts.
  16. 16. 3D MODELLING  3D Modelling is a multi-stage process.  Representation  Build a model of 3D Objects  Shapes  Surface textures  Sometimes using bitmaps.  Rendering  Geometric translations  Projection to 2D  Light representation
  18. 18. SIMPLE 3D OBJECT (x1,y1,z1) (x2,y2,z2) (x3,y3,z3) (x4,y4,z4) (x5,y5,z5) (x6,y6,z6) (x7,y7,z7)(x8,y8,z8) © Glenn Rowe
  20. 20. 3D REPRESENTATIONS  Complex shapes represented by polygons  Triangles and Rectangles mostly  Number of polygons defines the accuracy of the representation
  21. 21. TRANSFORMATIONS  Transformations used in 3D to manipulate images.  Three main transformations used in Blender.  Grab (translate)  Used to move shapes around fixed axis  Rotate  Used to rotate shapes around a fixed axis  Scale  Used to scale shapes up or down  Underlying representation done using matrix manipulation.
  22. 22. PROJECTION  Projection is the process that transforms 3D objects onto a 2D plane.  Three co-ordinate models.  Local, defines the shape’s vertexes  World space, defines the shape in relation to other shapes.  Viewing space, defines the location and size of the shape when displayed on the monitor.  Process turns {x,y,z} into just {x,y}
  23. 23. PROJECTION STYLES  Parallel Projection  Shows relationship between objects  Not realistic View plane 3D object
  24. 24. PROJECTION STYLES  Perspective Projection  Represents objects more realistically by converging vertexes at a point.  Foreshortening permits perspective. View plane 3D object Centre of projection
  25. 25. PROJECTION  Both assume a camera location.  The camera defines our view on the world.  To change the view of an object, we can:  Move the camera  Move the object.  Must get our heads around a viewport that has no fixed representation in the world space.
  26. 26. SUMMARY  Next three weeks about 3D graphics.  Using Blender.  3D Graphics consist of  Representation of objects  Representation of a world  Representation of a view port  Rendering  Complex transforms applied to turn 3D representation into 2D view.