COMPUTER GRAPHICS SPRING 2015 DR. MICHAEL J. REALE DEFINITION AND - - PowerPoint PPT Presentation

CS 548: COMPUTER GRAPHICS INTRODUCTION TO COMPUTER GRAPHICS

SPRING 2015

• DR. MICHAEL J. REALE

DEFINITION AND APPLICATIONS

WHAT IS COMPUTER GRAPHICS?

• Computer graphics – generating and/or displaying imagery using computers
• Also touches on problems related to 3D model processing, etc.
• The focus of this course will be on the underlying mechanics and algorithms of computer graphics
• As opposed to a computer art course, for instance, which focuses on using tools to make graphical content

SO, WHY DO WE NEED IT?

• Practically EVERY field/discipline/application needs to use computer graphics in some way
• Science
• Art
• Engineering
• Business
• Industry
• Medicine
• Government
• Entertainment
• Advertising
• Education
• Training
• …and more!

APPLICATIONS: GRAPHS, CHARTS, AND DATA VISUALIZATION

• Graphics and charts
• One of the earliest applications  plotting data using printer
• Data visualization
• Sciences
• Show visual representation  see patterns in data
• E.g., the flow of fluid (LOx) around a tube is described using streamtubes
• Challenges: large data sets, best way to display data
• Medicine
• 2D images (CT, MRI scans)  3D volume rendering
• E.g., volume rendering and image display from the visible woman dataset

Images from VTK website: http://www.vtk.org/VTK/project/imagegallery.php

APPLICATIONS: CAD/CADD/CAM

• Design and Test
• CAD = Computer-Aided Design
• CADD = Computer-Aided Drafting and Design
• Usually rendered in wireframe
• Manufacturing
• CAM = Computer-Aided Manufacturing
• Used for:
• Designing and simulating vehicles, aircraft,

mechanical devices, electronic circuits/devices,…

• Architecture and rendered building designs
• ASIDE: Often need special graphics cards to make absolutely SURE the rendered image is correct (e.g., NVIDIA

Quadro vs. a garden-variety Geforce)

http://www.nvidia.com/object/siemens-plm-software-quadro-visualization.html

GAMES!!!

APPLICATIONS: COMPUTER ART / MOVIES

• First film to use a scene that was completely computer generated:
• Tron (1982)
• Star Trek II: Wrath of Khan (1982)
• …(depends on who you talk to)
• First completely computer-generated full-length film:
• Toy Story (1995)

http://upload.wikimedia.org/wikipedia/en/1/17/Tron_poster.jpg http://blog.motorcycle.com/wp-content/uploads/2008/10/tron_movie_image_light_cycles__1_.jpg https://bigcostas.files.wordpress.com/2007/12/genesis1.jpg http://www.standbyformindcontrol.com/wp-content/uploads/2013/05/khan-poster.jpg http://s7d2.scene7.com/is/image/Fathead/15- 15991X_dis_toy_story_prod?layer=comp&fit=constrain&hei=350&wid=350&fmt=png- alpha&qlt=75,0&op_sharpen=1&resMode=bicub&op_usm=0.0,0.0,0,0&iccEmbed=0

APPLICATIONS: VIRTUAL-REALITY ENVIRONMENTS / TRAINING SIMULATIONS

• Used for:
• Training/Education
• Military applications (e.g., flight simulators)
• Entertainment

https://dbvc4uanumi2d.cloudfr

• nt.net/cdn/4.3.3/wp-

content/themes/oculus/img/or der/dk2-product.jpg

"Virtuix Omni Skyrim (cropped)" by Czar - Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Virtuix_Omni_Skyrim_(cropped).jpg#mediaviewer/File:Virtuix_Omn i_Skyrim_(cropped).jpg

APPLICATIONS: GAMES!

Unreal 4 Engine Crytek 3 Engine

APPLICATIONS: GAMES!

Unity Engine (Wasteland 2) Source Engine (Portal 2)

APPLICATIONS: GAMES!

Wolfenstein: Then and Now

http://www.dosgamesarchive.com/download/wolfenstein-3d/ http://mashable.com/2014/05/23/wolfenstein-then-and-now/ http://www.gamespot.com/images/1300-2536458

CHARACTERISTICS OF COMPUTER GRAPHICS

• Depending on your application, your focus and goals will be different:
• Real-time vs. Non-real-time
• Virtual Entities / Environments vs. Visualization / Representation
• Developing Tools / Algorithms vs. Content Creation

CG CHARACTERISTICS: REAL-TIME VS. NON-REAL-TIME

• Real-time rendering
• 15 frames per second (AT BARE MINIMUM – still see skips but it will look more or less animated)
• 24 fps = video looks smooth (no skips/jumps)
• 24 – 60 fps is a more common requirement
• Examples: first-person simulations, games, etc.
• Non-real-time
• Could take hours for one frame
• Examples: CG in movies, complex physics simulations, data visualization, etc.
• Often trade-off between speed and quality (image, accuracy, etc.)

CG CHARACTERISTICS: VIRTUAL ENTITIES / ENVIRONMENTS VS. VISUALIZATION / REPRESENTATION

• Virtual Entities / Environments
• Rendering a person, place, or thing
• Often realistic rendering, but it doesn’t have to be
• Examples: simulations (any kind), games, virtual avatars, movies
• Visualization / Representation
• Rendering data in some meaningful way
• Examples: graphics/charts, data visualization, (to a lesser extent) graphics user

interfaces

• Both
• Rendering some object / environment, but also highlighting important

information

• Examples: CAD/CAM

Remy from Pixar’s Ratatouille: http://disney.wikia.com/wiki/ Remy

Face using Crytek engine: http://store.steampo wered.com/app/220 980/

Tiny and Big: Grandpa’s Leftovers game: http://www.mobygames.com/game/windows/tiny-and-big- grandpas-leftovers/screenshots/gameShotId,564196/

http://www.vtk.org/VTK/project/imagegallery.php

CG CHARACTERISTICS: TOOLS/ALGORITHMS VS. CONTENT CREATION

• Developing Tools / Algorithms
• It’s…well…developing tools and algorithms for graphical purposes
• Using computer-graphics application programming interfaces (CG API)
• Common CG APIs: GL, OpenGL, DirectX, VRML, Java 2D, Java 3D, etc.
• Interface between programming language and hardware
• Also called “general programming packages” in Hearn-Baker book
• Example: how do I write code that will render fur realistically?
• Content Creation
• Using pre-made software to create graphical objects
• Called “special purpose software packages” in Hearn-Baker book
• Example: how do I create a realistic-looking dog in a 3D modeler program?

THIS COURSE

• In this course, we’ll mostly be focusing on developing tools / algorithms to render in real-time virtual

entities / environments

VIDEO DISPLAY DEVICES

INTRODUCTION

• A lot of why computer graphics works the way it does is based in the hardware
• Graphics cards, display devices, etc.
• In this section, we’ll talk about video display devices (and some of the terminology associated with them)
• CRT
• Plasma
• LCD/LED
• 3D
• For an excellent explanation of how…
• LCD/LED monitors work: http://electronics.howstuffworks.com/lcd.htm
• Plasma monitors work: http://electronics.howstuffworks.com/plasma-display.htm

CRT: CATHODE-RAY TUBE

• Primary video display mechanism for a long time
• Now mostly replaced with LCD monitors/TVs
• Cathode = an electrode (conductor) where electrons

leave the device

• Cathode rays = beam of electrons
• Basic idea:
• Electron gun (cathode + control grid) shoots electrons in vacuum tube
• Magnetic or electric coils focus and deflect beam of electrons so they hit each

location on screen

• Screen coated with phosphor  glows when hit by electrons
• Phosphor will fade in a short time  so keep directing electron beam over same

screen points

• Called refresh CRT

By Theresa Knott (en:Image:Cathode ray Tube.PNG) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons

http://i.imgur.com/ayHx5.jpg?1

DISPLAY DEFINITIONS

• Refresh rate = frequency that picture is redrawn
• Term still used for things other than CRTs
• Usually expressed in Hertz (e.g., 60 Hz)
• Persistence = how long phosphors emit light after being hit by electrons
• Low persistence  need higher refresh rates
• LCD monitors have an analogous concept  response time

MORE DISPLAY DEFINITIONS

• Pixels = “picture element”; single point on screen
• Resolution = maximum number of points that can be displayed without overlap
• For CRTs  more analogue device, so definition is a little more involved
• Now, usually just means (number of pixels in width) x (number of pixels in height)
• Aspect ratio = resolution width / height
• (Although sometimes vice versa)

TYPES OF CRT MONITORS

• There were two basic types of CRT monitors:
• Vector displays
• Raster-scan displays

CRT: VECTOR DISPLAYS

• Also called random-scan, stroke-writing, or calligraphic displays
• Electron beam actually draws points, lines, and curves directly
• List of things to draw stored in display list (also called refresh

display file, vector file, or display program)

• Long list  just draw as quick as you can
• Short list  delay refresh cycle so you don’t burn out screen!
• Advantages: draws non-aliased lines
• Disadvantages: not very flexible; cannot draw shaded polygons
• Mostly abandoned in favor of raster-scan displays

CRT: RASTER-SCAN DISPLAYS

• Most common type of CRT
• Refresh buffer (or frame buffer) = contains picture of

screen you want to draw

• Electron gun sweeps across screen, one row at a time,

from top to bottom

• Each row = scan line
• Advantages: flexible
• Disadvantages: lines, edge, etc. can look jagged (i.e.,

aliased)

CRT: INTERLACING

• Interlacing = first draw even-numbered scan lines,

then do odd-numbered lines

• Effectively doubles your refresh rate
• Also used to save data in TV transmission

CRT: COLOR

• Two ways to do color with CRTs:
• Beam-penetration
• Have red and green layer of phosphors
• Slow electrons  only red lay
• Fast electrons  only green layer
• Medium-speed electrons  both
• Inexpensive, but limited in number of colors
• Shadow-mask
• Uses red-green-blue model for color (RGB)
• Three electron guns and three phosphor dots (one for red,
• ne for green, and one for blue)
• Shadow mask makes sure 3 guns hit the 3 dots

PLASMA DISPLAYS

• Fill region between two glass plates with mixture of gases (usually

includes neon)

• Vertical conducting ribbons on one plate; horizontal conducting ribbons
• n the other
• Firing voltages at intersecting pair of horizontal and vertical conductors 

gas at intersection breaks down into glowing plasma of electrons and ions

• For color  use three subpixels (red, green, and blue)
• Advantages: very thin display; pixels very bright, so good at any angle
• Disadvantages: expensive

http://electronics.howstuffworks.com/plasma-display2.htm

LCD DISPLAYS

• LCD = Liquid Crystal Displays
• Liquid crystal = maintain a certain structure, but can move

around like liquid

• Structure is twisted, but applying electrical current straightens it out
• Basic idea:
• Two polarized light filters (one vertical, one horizontal)
• Light passes through first filter  polarized light in vertical direction
• “ON STATE”  no current  crystal twisted  causes light to be

reoriented so it passes through horizontal filter

• “OFF STATE”  current  crystal straightens out  light does NOT

pass through

LCD DISPLAYS: WHERE DOES THE LIGHT COME FROM?

• Mirror in back of display
• Cheap LCD displays (e.g., calculator)
• Just reflects ambient light in room (or prevents it from reflecting)
• Fluorescent light in center of display
• LED lights
• Could be edge-lit or full array (i.e., LEDS covering entire back of screen)
• Usually what people mean when they say an “LED monitor” = LCD display backlit by LEDs

LCD DISPLAYS: PASSIVE VS. ACTIVE

• Passive-matrix LCDs  use grid that sends charge to pixels through transparent conductive materials
• Simple
• Slow response time
• Imprecise voltage control
• When activating one pixel, nearby pixels also turned on  makes image fuzzy
• Active-matrix LCDs  use transistor at each pixel location using thin-film transistor technology
• Transistors control voltage at each pixel location  prevent leakage to other pixels
• Control voltage get 256 shades of gray

LCD DISPLAYS: COLOR

• Color  have 3 subpixels (one red, one green, and one blue)

http://electronics.howstuffworks.com/lcd5.htm

3D DISPLAYS: INTRODUCTION

• In real life, we see depth because of we have two eyes (binocular vision)
• One eye sees one angle, the other sees another
• Brain meshes two images together to figure out how far away things are
• By “3D” displays, we mean giving the illusion of depth by purposely giving each eye a different view

3D DISPLAYS: OLDER APPROACHES

• Anaglyph 3D
• Red and blue 3D glasses
• Show different images (one more reddish, the other more blue-ish)
• Color quality (not surprisingly) is not that great
• View Master toys
• First introduced 1939
• Take photograph at two different angles

http://science.howstuffworks.com/3-d-glasses2.htm

http://www.ebay.com/gds/How-to-Make-a-View-Master-Reel- /10000000178723069/g.html

3D DISPLAYS: ACTIVE 3D

• Active 3D
• Special “shutter” glasses that sync up with monitor TV
• Showing only one image at time (but REALLY fast)
• Show left image on TV  glasses close right eye
• Show right image on TV  glasses close left eye
• Advantages:
• If your monitor/TV has a high enough refresh rate, you’re good to go
• See full screen resolution
• Disadvantages:
• If out of sync, see flickering
• Image can look darker overall
• Glasses can be cumbersome

http://www.nvidia.com/object/product-geforce-3d-vision2-wireless- glasses-kit-us.html

3D DISPLAYS: PASSIVE 3D

• Passive 3D
• Polarized light glasses
• TV shows two images at once
• Uses alternating lines of resolution
• Similar to red-blue glasses, but color looks right
• Advantages:
• Glasses are lightweight
• Image is brighter than active 3D
• Disadvantages:
• Need special TV
• Only seeing HALF the vertical resolution!

Left: Passive 3D through glasses - Middle: Passive 3D without glasses - Right: Active 3D http://www.cnet.com/news/active-3d-vs-passive-3d-whats-better/

3D DISPLAYS: VR

• Virtual reality displays (like the Oculus Rift) basically have two separate screens (one for each eye)
• Advantages: no drop in resolution or brightness
• Disadvantages: heavy headset

http://www.engadget.com/2013/09/30/vorpx-beta-launch/

THE GRAPHICS RENDERING PIPELINE

DEFINITIONS

• Graphics Rendering Pipeline
• Generates (or renders) a 2D image given a 3D scene
• AKA the “pipeline”
• A 3D scene contains:
• A virtual camera – has a position and orientation (which way it’s point and which way is up), like in the image

above

• 3D Objects – stuff to render; have position, orientation, and scale
• Light sources - where the light is coming from, what color the light is, what kind of light is it, etc.
• Textures/Materials – determine how the surface of the objects should look

We’ve got this… …and we want this

PIPELINE STAGES

• The Graphics Rendering Pipeline can be divided into 3 broad stages:
• Application
• Determined by (you guessed it) the application you’re running
• Runs on CPU
• Example operations: collision detection, animation, physics, etc.
• Geometry
• Computes what will be drawn, how it will be drawn, and where it will be drawn
• Deals with transforms, projections, etc. (we’ll talk about these later)
• Typically runs on GPU (graphics processing unit, or your graphics card)
• Rasterizer
• Renders final image and performs per-pixel computations (if desired)
• Runs completely on GPU
• Each of these stages can also be pipelines themselves

PIPELINE SPEEDS

• Like any pipeline, only runs as fast as slowest stage
• Slowest stage (bottleneck)  determines rendering speed
• Rendering speed usually expressed in:
• Frames per second (fps)
• Hertz (1/seconds)
• Rendering speed  called throughput in other pipeline contexts

APPLICATION STAGE

• Programmer has complete control over this
• Can be parallelized on CPU (if you have the cores for it)
• Whatever else it does, it must send geometry to be rendered to the

Geometry Stage

• Geometry – rendering primitives, like points, lines, triangles, polygons, etc.

DEFINING 3D OBJECTS

• A 3D object (or 3D model) is defined in term of geometry or geometric primitives
• Vertex = point
• Most basic primitives:
• Points

(1 vertex)

• Lines

(2 vertices)

• Triangles

(3 vertices)

• MOST of the time, an object/model is defined as a triangle mesh

DEFINING 3D OBJECTS

• Why triangles?
• Simple
• Fits in single plane
• Can define any polygon in terms of triangles
• At minimum, a triangle mesh includes:
• Vertices
• Position in (x,y,z)  Cartesian coordinates
• Face definitions
• For each face, a list of vertex indices (i.e., which vertices go with which triangle)
• Vertices can be reused
• (Optional) Normals, texture coordinates, color/material information, etc.

DEFINING 3D OBJECTS

• In addition to points, lines, and triangles, other primitives exist such as:
• Polygons
• Again, however, you can define any polygon in terms of triangles
• Circles, ellipses, and other curves
• Often approximated with line segments
• Splines
• Also often approximated with lines (or triangles, if using splines to define a 3D surface)
• Sphere
• Center point + radius
• Often approximated with triangles

DEFINING 3D OBJECTS

• Sometimes certain kinds of 3D shapes are referred to as “primitives” (but ultimately these are often

approximated with a triangle mesh)

• Cube
• Sphere
• Torus
• Cylinder
• Cone
• Teapot

ASIDE: WAIT, TEAPOT?

• The Utah teapot or Newell teapot
• In 1975, Martin Newell at the University of Utah needed a 3D model, so he

measured a teapot and modeled it by hand

• Has become a very standard model for testing different graphical effects (and a bit
• f an inside joke)

Original drawing of the teapot: http://www.computerhistory.org/revolution/ computer-graphics-music-and-art/15/206 http://community.thefoundry.co.uk/discussion/topic.aspx?f=8&t=33283

GEOMETRY STAGE

• Performs majority of per-polygon and per-vertex operations
• In days of yore (before graphics accelerators), this stage ran on the CPU
• Has 5 sub-stages
• Model and View Transform
• Vertex Shading
• Projection
• Clipping
• Screen Mapping

MODEL COORDINATES

• Usually the vertices of a polygon mesh are relative to the

model’s center point (origin)

• Example: vertices of a 2D square
• (-1,1)
• (1,1)
• (1,-1)
• (-1,-1)
• Called modeling or local coordinates
• Before this model gets to the screen, it will be transformed into several different spaces or coordinate

systems

• When we start, the vertices are in model space (that is, relative to the model itself)

GEOMETRY STAGE: MODEL TRANSFORM

• Let’s say I have a teapot in model coordinates
• I can create an instance (copy) of that model

in the 3D world

• Each instance has its own model transform
• Transforming model coordinates  to world

coordinates

• Coordinates are now in world space
• Transform may include translation, rotation,

scaling, etc.

Different model transforms

RIGHT-HAND RULE

• Before we go further with coordinate spaces, etc., we need to talk about which way the x, y, and z axes

go relative to each other

• OpenGL (and other systems) use the right-hand rule
• Point right hand toward X, with palm up towards Y  thumb points toward Z

GEOMETRY STAGE: VIEW TRANSFORM

• Only things visible by the virtual camera will be rendered
• Camera has a position and orientation
• The view transform will transform both the camera and all objects so that:
• Camera starts at world origin (0,0,0)
• Camera points in direction of negative z axis
• Camera has up direction of positive y axis
• Camera is set up up such that the x-axis points to right
• NOTE: This is with the right-hand rule setup (OpenGL)
• DirectX uses left-hand rule
• Coordinates are now in camera space (or eye space)

OUR GEOMETRIC NARRATIVE THUS FAR…

• Model coordinates  MODEL TRANSFORM  World coordinates  VIEW TRANSFORM  Camera coordinates
• Or, put another way:
• Model space  MODEL TRANSFORM  World space  VIEW TRANSFORM  Camera (Eye) space

GEOMETRY STAGE: VERTEX SHADING

• Lights are defined in the 3D scene
• 3D objects usually have one or more materials attached to them
• So, a metal can model might have a metallic-looking material, for instance
• Shading – determining the effect of a light (or lights) on a material
• Vertex shading – shading calculations using vertex information
• Vertex shading is programmable!
• I.e., you have a great deal of control over what happens during this stage
• We’ll talk about this in more detail later; for now, know that the geometry stage handles this part…

GEOMETRY STAGE: PROJECTION

• View volume – area inside camera’s view that contains the objects we must render
• For perspective projections, called view frustum
• Ultimately, we will need to map 3D coordinates to 2D coordinates (i.e., points on the screen)  points

must be projected from three dimensions to two dimensions

• Projection – transforms view volume into a unit cube
• Converts world coordinates  normalized device coordinates
• Simplifies clipping later
• Still keep z coordinates for now
• In OpenGL, unit cube = (-1,-1,-1) to (1,1,1)

GEOMETRY STAGE: PROJECTION

• Two most commonly used projection methods:
• Orthographic (or parallel)
• View volume = rectangular box
• Parallel lines remain parallel
• Perspective
• View volume = truncated pyramid with rectangular base  called view frustum
• Things look smaller when farther away

Orthographic Perspective

GEOMETRY STAGE: CLIPPING

• What we draw is determined by what’s in the view volume:
• Completely inside  draw
• Completely outside  don’t draw
• Partially inside  clip against view volume and only draw part inside view volume
• When clipping, have to add new vertices to primitive
• Example: line is clipped against view volume, so a new vertex is added where the line intersects with the view

volume

GEOMETRY STAGE: SCREEN MAPPING

• We now have our (clipped) primitives in normalized device coordinates (which are still 3D)
• Assuming we have a window with a minimum corner (x1, y1) and maximum corner (x2, y2)
• Screen mapping
• x and y of normalized device coordinates  x’ and y’ screen coordinates (also device coordinates)
• z coordinates unchanged
• (x’,y’,z) = window coordinates = screen coordinates + z
• Window coordinates passed to rasterizer stage

GEOMETRY STAGE: SCREEN MAPPING

• Where is the starting point (origin) in screen coordinates?
• OpenGL  lower-left corner (Cartesian)
• DirectX  sometimes the upper-left corner
• Pixel = picture element
• Basically each discrete location on the screen
• Where is the center of a pixel?
• Given pixel (0,0):
• OpenGL  0.5, 0.5
• DirectX  0.0 ,0.0

In OpenGL

RASTERIZER STAGE

• Have transformed and projected vertices with associated shading data from geometry stage
• Primary goal  rasterization (or scan conversion)
• Computing and setting colors for pixels covered by the objects
• Convert 2D vertices + z value + shading info  pixels on screen
• Has four basic stages:
• Triangle setup
• Triangle traversal
• Pixel shading
• Merging
• Runs completely on GPU

RASTERIZER STAGE: TRIANGLE SETUP AND TRIANGLE TRAVERSAL

• Triangle setup
• Performs calculations needed for next stage
• Triangle Traversal (or Scan Conversion)
• Finds which samples/pixels are inside each triangle
• Generates a fragment for each part of a pixel covered by a triangle
• Fragment properties  interpolated from triangle vertices

RASTERIZER STAGE: PIXEL SHADING

• Performs per-pixel shading computations using interpolated shading data from previous stage
• Example: texture coordinates interpolated across triangles  get correct texture value for each pixel
• Output: one or more colors for each pixel
• Programmable!

FRAGMENT DEFINITION

• Fragment = data necessary to shade/color a pixel due to a primitive covering or partially covering that

pixel

• Data can include color, depth, texture coordinates, normal, etc.
• Values are interpolated from primitive’s vertices
• Can have multiple fragments per pixel
• Final pixel color will either be one of the fragments (i.e., z-buffer chooses nearest one) or combination of

fragments (e.g., alpha blending)

RASTERIZER STAGE: MERGING

• Color buffer  stores color for each pixel
• Merging stage  combine each fragment color with color current stored in color buffer
• Need to check if fragment is visible  e.g., with a Z-buffer
• Check z value of incoming fragment
• If closer to camera than previous value in Z-buffer  override color in color buffer and update z value
• Advantages:
• O(n)  n = number of primitives
• Simple
• Can draw OPAQUE objects in any order
• Disadvantages:
• Transparent objects more complicated

RASTERIZER STAGE: MERGING

• Frame buffer
• Means all buffers on system (but sometimes just refers to color + Z-buffer)
• To prevent the user from seeing the buffer while it’s being updated  use double-buffering
• Two buffers, one visible and one invisible
• Draw on invisible buffer  swap buffers

FIXED-FUNCTION VS. PROGRAMMABLE

• Fixed-function pipeline stages
• Elements are set up in hardware a specify way
• Usually can only turn things on or off or change options (defined by hardware and graphics API)
• Programmable pipeline stages
• Vertex shading and pixel (fragment) shading
• Have direct control over what is done at given stage

OTHER PIPELINES

• The outline we described is NOT the only way to do a graphics pipeline
• E.g., ray tracing renderers  pretty much do EVERYTHING in software, and then just set the pixel color with the

graphics card

COMPUTER GRAPHICS API

DEFINITIONS

• Computer-graphics application programming interfaces (CG API)
• Common CG APIs: GL, OpenGL, DirectX, VRML, Java 2D, Java 3D, etc.
• Interface between programming language and hardware
• Let’s briefly go over some CG APIs…

GKS AND PHIGS

• GKS (Graphical Kernel System) – 1984
• International effort to develop standard for computer graphics software
• Adopted as first graphics software standard by ISO (International Standards Organization) and ANSI (American National Standards

Institute)

• Original 2D  3D extension developed later
• PHIGS (Programmer’s Hierarchical Interactive Graphics Standard)
• Extension of GKS
• Developed in 1980’s  standard by 1989
• 3D standard
• Increased capabilities for hierarchical modeling, color specifications, surface rendering, and picture manipulations
• PHIGS+  added more advanced 3D surface rendering

GL AND OPENGL

• GL (Graphics Library)
• Developed by Silicon Graphics, Inc. (SGI) for their graphics workstations
• Became de facto graphics standard
• Fast, real-time rendering
• Proprietary system
• OpenGL
• Developed as hardware-independent version of GL in 1990’s
• Specification
• Was maintained/updated by OpenGL Architecture Review Board; now maintained by

the non-profit Khronos Group

• Both are consortiums of representatives from many graphics companies and organizations
• Designed for efficient 3D rendering, but also handles 2D (just set z = 0)
• Stable; new features added as extensions

SGI O2 workstation: http://www.engadget.com/products/sgi/o2/

DIRECTX AND DIRECT3D

• DirectX
• Developed by Microsoft for Windows 95 in 1996
• Originally called “Game SDK”
• Actually combinations of different APIs: Direct3D, DirectSound, DirectInput, etc.
• Less stable  adopts new features fairly quickly (for better or for worse)
• Only works on Windows and Xbox

WHY ARE WE USING OPENGL?

• In this course, we will be using OpenGL because:
• It works with practically ever platform/system (Windows, Unix/Linux, Mac, etc.)
• It’s arguably easier to learn/understand
• It is NOT because DirectX/Direct3D is a bad system

REFERENCES

• Many of the images in these slides come from the book “Real-Time Rendering” by Akenine-Moller,

Haines, and Hoffman (3rd Edition) as well as the online supplemental material found on their website: http://www.realtimerendering.com/

• Some also are from the book “Computer Graphics with OpenGL” by Hearn, Baker, and Carithers (4th

edition)