Computer Graphics and its Components

CG (Cont)ApplicationDataStructuresApplicationProgramsGraphicsSystemsGraphics DevicesUsers(operators)Application Data Structures / ModelsApplication ProgramsGraphics SystemsGraphics DevicesThe Programmers Model of Interactive Graphics

Output DevicesDisplay DevicesHard Copy Devices

Input DevicesLocatorStrokeString (Keyboard)ValuatorChoice (Button)Pick1. Graphics Devices

1.1 Output DevicesCRT BasicsDPDVST (Direct View Storage Tube)Refresh DisplayRaster - Scan DisplayOthersCPUDPMemoryHard CopyDisplayInputCRT Displays

HorizontalDeflectionPlatePhosphor-CoatedScreenHeatingFilamentControlGridAcceleratingSystemVerticalDeflectionPlateElectron BeamFocusingSystemCathodeCRT Basics

CRT BasicsIntensity of the electron beam is controlled by setting voltage levels on the control grid, which is a metal cylinder that fits over the cathode.

Phosphor dot patternDifferent phosphor for each color !!!Color CRT (Shadow Mask)

Delta-delta shadow-mask CRTPrecision in-line delta CRT

A CRT monitor displays color pictures by using a combination of phosphors that emit different-colored light. By combining the emitted light from the different phosphors, a range of colors can be generated. The two basic techniques for producing color displays with a CRT are the beam-penetration method and the shadow-mask method.The beam-penetration method for displaying color pictures has been used with random-scan monitors. Two layers of phosphor, usually red and green, are coated onto the inside of the CRT screen, and the displayed color depends on how far the electron beam penetrates into the phosphor layers.

Shadow-mask methods are commonly used in rasterscan systems (including color TV) because they produce a much wider range of colors than the beampenetration method. A shadow-mask CRT has three phosphor color dots at each pixel position. One phosphor dot emits a red light, another emifs a green light,and the third emits a blue light. This type of CRT has three electron guns, one for each color dot, and a shadow-mask grid just behind the phosphor-coated screen.

Refresh rate# of times/sec a picture is redrawn60 Hz for raster scan displaysIntensity10 %TimeRefreshingPersistence

energyspot sizedistanceelectron beam0.5 ~ 0.61Sharpness

The effect of cross-sectional spot intensity on resolution

The effects of various ratios of the dot size to the interdot distance

The aspect ratio of a display device is the ratio of the number of vertical points to that of horizontal points necessary to produce equal length of lines in both direction on screenNoteSometimes, aspect ratio is stated in terms of the ratio of horizontal to vertical points3/4 = 0.754/3 = 1.33...Aspect Ratio

Why DP ?Scan conversionRefreshingRaster operationsCharacter generationInterfacing with interactive input devices

DP (Display Processor)

Refresh CRT (Vector CRT)DisplayprocessorCRTAlphanumeric keyboardStylusData tabletInterface tohost computerMOVE 10 15LINE 100 25CHAR LU CYLINEJMPRefresh buffer memory(Display commands)(interaction data)

CPUDPURefreshbufferInput(Display file)CRTWhat is the display file ?DPU program !!!What if a picture is complicated ?Longer DPU program !!!

The size of the refresh buffer limits the complexity of a picture

Dynamic picture updateSelective erasing

A complex picture may cause flickering !!!

Refresh rate30 frame / secdepending on the complexity of a picture

DVST (Direct View Storage Tube)DisplayprocessorCRTKeyboardVertical andHorizontal cursorthumbwheelsInterface to host computer(Display commands)(interaction data)

No refresh buffer !!!Why ?

random accessflicker-freestatic (no selective erasing)

Raster-Scan DisplayDisplayprocessorCRTInterface to host computer(Display commands)(interaction data)KeyboardData input000000000000000000000000010000000000000000000000000000000100000000000000000000000000000111110000000000000110000000011111111111110000000011110000000000011111000000000011111111000000000001000000000011111111111100000000010000000011111111111111110000000000000000011111111111111000000000000000000111111111111110000000000000000001111111111111100000000000000000000000000000000000000000000000Frame buffer

Selective erasingFixed frame buffer sizeIndependent of picture complexity

A raster-scan system displays an object as a set of points across each screen scan line(a)(b)(d)(c)

Interlacing

NTSC (National Television System Committee)Aspect ratioRefresh rate : 30 Hz34483FrameEven scan line fieldOdd scan line fieldVisible oddscan linesOdd scan linevertical retraceVisible evenscan linesEven scan linevertical retrace241 1/2 lines21 lines241 1/2 lines21 lines262 1/2 lines262 1/2 lines525 linesPALSECAM64417% of time for a scanline is used for horizontal retrace

Frame buffer for B/W display

Frame buffer for N-bit nanochrome display

Palette(look-up table)

Frame buffer for color CRT

scan conversionmemory accessSimple Raster Display System

scan conversion raster operationsCharacter generation I/O transfer on the system busRaster Display System with Display Processor

cache memories video RAM (VRAM) (read out all pixels on a scan line in one cycle)Single-Address-Space Raster Display System

ReflectivelayerHorizontalpolarizerHorizontalgrid wiresLiquid-crystallayerVerticalgrid wiresVerticalpolarizerViewingdirectionLCD ( Liquid Crystal Display ) Basics

Color TFT (Thin Film Transistor) LCDColor ?Liquid CrystalTFT (Thin Film Transistor) using a transistor at each grid point causing the crystals to change their state quickly controlling the degree to which the state has been changed holding the state until it changesTFTColor Filter

Other Display DevicesPlasma-Panel DisplaysLaser DevicesThree-Dimensional MonitorsHMDs

Hard Copy DisplaysPrintersPlotters3D-printers

1.2 Input DevicesPhysical DevicesLogical DevicesInput ModesRequest modeSample modeEvent mode

KeyboardsPhysical Devices

Dials

Touch Panels

Light Pens

Graphics Tablets

3D-Tablets

Joysticks / Mice / Trackballs

Buttons

Voice Systems

LocatorStrokeStringValuatorChoicePickLogical Devices

Locator Devices / Stroke Devices

y + y - axis (a)(b)String Devices

180Valuator Devices

Buttons

Menu SelectionChoice Devices

Pick Devices

2. Graphics SystemsInterface between application programs and graphics devicesConsisting of input subroutines and output subroutines accepting input data from input devices and draw pictures on output devices, respectively

Application program

Graphics systemGraphicshardwareInput andoutput devicesACM Core,GKS, GKS-3DCGI (device interface)CGM (metafile)PHIGS (3D and realtime)PHIGS+ X-windowOpenGLPEXDirectXMetafilesOperating system2.1 Overview

API (Application Programmer Interface) to interactive 3D renderingState machine to facilitate a 3D rendering pipelineClient-server model250 distinct commandsTo drive the rendering pipelineTo control the state of the pipeline by a set of parametersNo input commands2.2 OpenGL

Clients (Application) issue commandsThe server (OpenGL) interprets and processes commandsFrame buffer configuration taken care of by a window system2.3 Client-server Model

Window tasksInput devicesComplicated shapes

OpenGL Utility Library (GLU)Window system support librariesGLX / WGL / PGLOpenGL Utility Toolkit (GLUT)Fahrenheit Scene Graph (FSG)

For portability, there areno commands for these.2.4 OpenGL-related Libraries

Direct control of graphics hardwareDirect control of input devices, and soundApplication programWindows systemDirect soundDirect graphicsDirect inputWindows APIDirect X..2.5 DirectX

PC / MS WindowsVisual C++OpenGLPlatform for Course Projects

3. Application Data Structures/ Models3.1 Hierarchical Representation

objects:geometric data non-geometric dataABCAABBABC

OBJF1F2FkE1E2EnEmV1V2VrApplication Data Modeling (Cont)

DefinitionA collection of methods to define geometric and topological characteristics of an objectThree well-known geometric modelswireframe modelssurface modelssolid models3.2 Geometric Modeling

Primitives: points and linesApplications: 2D CAD/CAM, DraftingP1P2P3P4P5P6P7P8Simple and efficientAmbiguousWireframe Models

lVLSI Design (design rule check)

Primitives: points, lines and patchesApplications: representation of sculptured surfaces, tool path calculationtsAccurate representation of curved surfaceCannot represent a true 3D volumeSurface Models

Machining

USolidCSG representationUBoundary representationShading & visibility determinationMass properties calculationInterference testSolid Models

What is feature?How can you extract feature?Feature Extraction

H1H2H3W1W2W3HULL(W1)HULL(W2)HULL(W3)H1 - W1H2 - W2H3 - W3Homework #1Alternating Sum of Volumes

H1H2H3H1 - H2H3CSG-Tree

How can you disassemble OBJ?EFABCDEFCABD Can you obtain an assembly sequence from it?Assembly

XYZsweepXYZsweepSwept Volume

Object Decomposition

Octree Representation

Modeler

CATIACATSOFTDOM-SOLIDSEUCLIDGEOMOD-IIICEM SOLID MODELINGICM GMSMEDUSAPADL-1.2PATRAN-GROMULUSSOLIDESIGNSOLID MODELING-IISYNTHAVISIONTIPS-1UNIS-CADUNISOLIDSVendor/Distributor

IBMCATRONIXCALMAMATRA DATAVISION/DECSDRC/GENERAL ELECTRIC CAECDCICMPRIMEU. ROCHESTERPOA ENGINEERINGEVANS & SUTHERLANDCOMPUTERVISIONAPPLICONMAG1CAM-ISPERRY UNIVACMCAUTOCore Software

DASSAULT (FRANCE)

CNRS (FRANCE)SDRCSYNTHAVISION (MAG1)

CIS/CV (UK)

SHAPENDATA (UK)

SYNTHAVISION (MAG1)

HOKKAIDO U.BAUSTEIN GEOMETRIC (T. U. BERLIN)PADL-2 (U. ROCHESTER)Genre

B-REPCSGB-REPB-REPB-REPCSGB-REPB-REPCSGCELL DECOMPB-REPB-REPCSGCSGCSGB-REPCSG

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Examples

CSGBasedSweepBasedB-Rep.BasedCSGB-Rep.SpatialDecomp.Input subsystemCore representation subsystemGeometric Modeling Systems

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