1 Graphics Device System

2 Acknowledgement I’d like to thank Pradondet Nilagupta who creates such a good work on these lecture notes.

3 Graphical System 5 major elements for a computer graphic system Processor Memory Frame buffer Input devices Output Devices

4 Output Technology (1/3) Calligraphic Displays also called vector, stroke or line drawing graphics lines drawn directly on phosphor display processor directs electron beam according to list of lines defined in a "display list“ phosphors glow for only a few micro-seconds so lines must be redrawn or refreshed constantly deflection speed limits # of lines that can be drawn without flicker.

5 Images are described in terms of line segments rather than pixels. Display processor cycles through the commands

6 Output Technology (2/3) Raster Display Display primitives (lines, shaded regions, characters) stored as pixels in refresh buffer (or frame buffer) Electron beam scans a regular pattern of horizontal raster lines connected by horizontal retraces and vertical retrace Video controller coordinates the repeated scanning Pixels are individual dots on a raster line

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8 Output Technology (cont) Bitmap is the collection of pixels Frame buffer stores the bitmap Raster display store the display primitives (line, characters, and solid shaded or patterned area) Frame buffers are composed of VRAM (video RAM). VRAM is dual-ported memory capable of Random access Simultaneous high-speed serial output: built-in serial shift register can output entire scanline at high rate synchronized to pixel clock.

9 Pros and Cons Advantages to Raster Displays lower cost filled regions/shaded images Disadvantages to Raster Displays a discrete representation, continuous primitives must be scan-converted (i.e. fill in the appropriate scan lines) Aliasing or "jaggies" Arises due to sampling error when converting from a continuous to a discrete representation

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12 Basic Definitions Raster: A rectangular array of points or dots. Pixel (Pel): One dot or picture element of the raster Scan line: A row of pixels Video raster devices display an image by sequentially drawing out the pixels of the scan lines that form the raster.

13 Resolution Maximum number of points that can be displayed without overlap on a CRT monitor REL SGI O2 monitors: 1280 x 1024

14 Example Television NTSC 640x480x8b 1/4 MB GA-HDTV 1920x1080x8b ~2 MB Workstations Bitmapped display 960x1152x1b ~1 Mb Color workstation 1280x1024x24b 5 MB Laserprinters 300 dpi (8.5”x300)(11”x300) 1.05 MB 2400 dpi (8.5”x2400)(11”x2400) ~64 MB

15 Aspect Ratio Frame aspect ratio (FAR) = horizontal/vertical size TV 4:3 HDTV 16:9 Page 8.5:11 ~ 3/4 Pixel aspect ratio (PAR) = FAR vres/hres Nuisance in graphics if not 1

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17 Physical Size Physical size: Length of the screen diagonal (typically 12 to 27 inches) REL SGI O2 monitors: 19 inches

18 Refresh Rates and Bandwidth Frames per second (FPS) TV (interlaced) 30 FPS x 1/4 = 8 MB/s

19 Interlaced Scanning Scan frame 30 times per second To reduce flicker, divide frame into two fields—one consisting of the even scan lines and the other of the odd scan lines. Even and odd fields are scanned out alternately to produce an interlaced image. 1/30 SEC 1/60 SEC FIELD 1FIELD 2 FRAME 1/60 SEC 1/30 SEC 1/60 SEC FIELD 1FIELD 2 FRAME 1/60 SEC

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21 Frame Buffer A frame buffer is characterized by size, x, y, and pixel depth. the resolution of a frame buffer is the number of pixels in the display. e.g. 1024x1024 pixels. Bit Planes or Bit Depth is the number of bits corresponding to each pixel. This determines the color resolution of the buffer. Bilevel or monochrome displays have 1 bit/pixel 8bits/pixel -> 256 simultaneous colors 24bits/pixel -> 16 million simultaneous colors

22 Specifying Color direct color : each pixel directly specifies a color value e.g., 24bit : 8bits(R) + 8bits(G) + 8 bits(B) palette-based color : indirect specification use palette (CLUT) e.g., 8 bits pixel can represent 256 colors 24 bits plane, 8 bits per color gun = 16,777,216

23 Lookup Tables Video controller often uses a lookup table to allow indirection of display values in frame buffer.

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26 Cathode Ray tube

27 Display Technology 2D Displays CRT LCD (raster) plasma screen (raster) Light valves (raster) Micromirror (raster) Projected laser (vector) Direct laser (vector) 3D Displays Stereo presentation (raster/vector) Vibrating mirror (vector) Helical rotor (vector) LED plate (raster) Photoactive cube (raster) Parabolic mirror (raster)

28 Display Technologies Cathode Ray Tubes (CRTs) Most common display device today Evacuated glass bottle (last of the vacuum tubes) Heating element (filament) Electrons pulled towards anode focusing cylinder Vertical and horizontal deflection plates Beam strikes phosphor coating on front of tube

29 Display Technologies: CRTs Vector Displays First computer displays: basically an oscilloscope Control X,Y with vertical/horizontal plate voltage Often used intensity as Z Show: Name two disadvantages Just does wireframe Display needs constant update to avoid fading

30 Vector Display Architecture

31 Display Technologies: CRTs Raster Displays Black and white television: an oscilloscope with a fixed scan pattern: left to right, top to bottom Paint entire screen 30 times/sec Actually, TVs paint top-to-bottom 60 times/sec, alternating between even and odd scanlines This is called interlacing. It’s a hack. Why do it? To paint the screen, computer needs to synchronize with the scanning pattern of raster Solution: special memory to buffer image with scan-out synchronous to the raster. We call this the framebuffer.

32 Raster displays Architecture

33 Raster refresh

34 Comparing Raster and Vector (1/2) advantages of vector: very fine detail of line drawings (sometimes curves), whereas raster suffers from jagged edge problem due to pixels (aliasing, quantization errors) geometry objects (lines) whereas raster only handles pixels eg line plot: vector disply computes 2000 endpoints raster display computes all pixels on each line

35 Comparing Raster and Vector (2/2) advantages of raster: cheaper colours, textures, realism unlimited complexity of picture: whatever you put in refresh buffer, whereas vector complexity limited by refresh rate

36 Display Technology: Color CRTs Color CRTs are much more complicated Requires manufacturing very precise geometry Uses a pattern of color phosphors on the screen: Delta electron gun arrangementIn-line electron gun arrangement

37 Display Technology: Color CRTs Color CRTs have Three electron guns A metal shadow mask to differentiate the beams

38 Display Technology: Raster CRT (raster) pros: Leverages low-cost CRT technology (i.e., TVs) Bright! Display emits light Cons: Requires screen-size memory array Discreet sampling (pixels) Practical limit on size (call it 40 inches) Bulky Finicky (convergence, warp, etc) X-ray radiation…

39 Display Technology: LCDs Liquid Crystal Displays (LCDs) LCDs: organic molecules, naturally in crystalline state, that liquefy when excited by heat or E field Crystalline state twists polarized light 90º.

40 LCDs Transmissive & reflective LCDs: LCDs act as light valves, not light emitters, and thus rely on an external light source. Laptop screen: backlit, transmissive display Palm Pilot/Game Boy: reflective display

41 Active-Matrix LCDs LCDs must be constantly refreshed, or they fade back to their crystalline state Refresh applied in a raster-like scanning pattern Passive LCDs: short-burst refresh, followed by long slow fade in which LCD is between On & Off Not very crisp, prone to ghosting Active matrix LCDs have a transistor and capacitor at every cell FET transfers charge into capacitor during scan Capacitor easily holds charge till next refresh

42 Active Matrix LCDs Pros and Cons Active-matrix pros: crisper with less ghosting,low cost, low weight,flat, small size, low power consumption. Active-matrix cons: more expensive, small size, low contrast, slow response Today, most things seem to be active-matrix More on Display

43 Plasma Plasma display panels Similar in principle to fluorescent light tubes Small gas-filled capsules are excited by electric field, emits UV light UV excites phosphor Phosphor relaxes, emits some other color

44 Plasma Display Panel Pros and Cons Plasma Display Panel Pros Large viewing angle Good for large-format displays Fairly bright Cons Still very expensive Large pixels (~1 mm versus ~0.2 mm) Phosphors gradually deplete Less bright than CRTs, using more power

45 Display Technology: DMDs Digital Micromirror Devices (projectors) Microelectromechanical (MEM) devices, fabricated with VLSI techniques

46 DMDs Pros and Cons DMDs are truly digital pixels Vary grey levels by modulating pulse length Color: multiple chips, or color-wheel Great resolution Very bright Flicker problems

47 FEDs Field Emission Devices (FEDs) Like a CRT, with many small electron guns at each pixel Unreliable electrodes, needs vacuum Thin, but limited in size

48 Organic LED Arrays Organic Light-Emitting Diode (OLED) Arrays The display of the future? Many think so. OLEDs function like regular semiconductor LEDs But with thin-film polymer construction: Thin-film deposition or vacuum deposition process…not grown like a crystal, no high-temperature doping Thus, easier to create large-area OLEDs

49 Organic LED Arrays Pros and Cons OLED pros: Transparent Flexible Light-emitting, and quite bright (daylight visible) Large viewing angle Fast (< 1 microsecond off-on-off) Can be made large or small OLED cons: Not quite there yet (96x64 displays…) Not very robust, display lifetime a key issue

50 Traditional Input Device (1/4) Commonly used today Mouse-like devices mouse wheel mouse trackball Keyboards

51 Pen-based devices pressure sensitive absolute positioning tablet computers IPAQ, WinCE machines Microsoft eTablet coming soon palm-top devices Handspring Visor, PalmOS™ Traditional Input Device (2/4)

52 Traditional Input Device (3/4) Joysticks game pads flightsticks Touchscreens Microphones wireless vs. wired headset

53 Traditional Input Device (4/4) Digital still and video cameras, scanners MIDI devices input from electronic musical instruments more convenient than entering scores with just a mouse/keyboard

54 3D Input Device (1/2) Electromagnetic trackers can be attached to any head, hands, joints, objects Polhemus FASTRAK™(used in Brown’s Cave) Acoustic-inertial trackers Intersense IS

55 3D Input Device (2/2) Gloves attach electromagnetic tracker to the hand Pinch gloves contact between digits is a “pinch” gesture in CAVE, extended Fakespace PINCH™ gloves with extra contacts

56 Video Output Devices (1/4) Classification Stereo head-mounted displays shutter glasses Degree of immersion conventional desktop screen walkup VR, semi- immersive displays immersive virtual reality equips/hmd.html

57 Video Output Devices (2/4) Example of Immersive Display Diffusion Tensor MRI Brain Visualization at Brown University

58 Video Output Devices (3/4) Desktop Vector display CRT LCD flatpanel workstation displays(Sun Lab) PC and Mac laptops Tablet computers Wacom’s display tablet

59 Video Output Devices (4/4) Immersive Head-mounted displays (HMD) Stereo shutter glasses Virtual Retinal Display (VRD) CAVE™

60 Interactive Input Devices A graphics work station commonly has one or two monitors and a range of input devices. These can include: Other device Graphics tabletMouse Light penJoystick Button devicesDials and levers 3D locatorsTouch panels Voice InputScanners Keyboard May be customized to application. Can include dials, joysticks.

61 Hard Copy Devices Printers Non-Impact printers --- Ink jet; laser; Xerographic; Electrostatic; Dye sublimation. Plotters Flatbed, Beltbed Multiple pens available Plotter `languages’ Built in character sets, line styles etc.

62 Hardcopy Technologies Basically printing on paper, film etc. Some general issues are: The resolution of a device is the closest spacing at which adjacent black and white lines can be distinguished. Many devices work by producing (colored) dots, and image quality vs. dot size or spot size is an issue. Resolution can be no greater than addressability (lines per inch) and depends on spot size also on intensity distribution across spot. Many devices can create only a few solid colors. Other colors must be produced by dither patterns.

63 Raster Scan Display Systems The various hardware architectures for providing graphics functionality differ on two axes Processing performed by specialized graphics hardware. Simplest has only video controller. More complex systems use a graphics display processor with varying functionality. Relationship of frame buffer to CPU memory architecture. Dual ported Accessible only to graphics controller Accessible only over main bus

64 Video Controller Problems with memory access { 50 ns pixel time (480 x 640 x 60 Hz) is shorter than typical 200 ns RAM cycle time. - Must fetch multiple pixels per access. - Can eat up a lot of memory bandwidth. - Can eat up a lot of main bus bandwidth if so organized.

65 Simple Raster systems (1/2) No special graphics processing except video controller. Two basic frame-buffer mappings. Single ported frame buffer Passes video information over system bus. Simple and flexible. Problems with bus congestion.

66 Simple Raster systems (2/2) Dual ported frame buffer: Frame buffer in special, dual ported Video RAM. Unloads bus. More expensive. Less exible.

67 Systems with video processors (1/3) Makes sense to put special-purpose hardware close to video (speed, expense) May do various scan conversion algorithms, pix moves, windowing, sometimes rotation of existing primitives Commands such as Text, Move, Line, Polygon... 3D stuff as well - hidden surface removal, shading, texture mapping. Various architectures.

68 Systems with video processors (2/3) Graphics processor has its local memory and manages the frame buffer and specialized graphics programs. Typical architecture for "plug in" graphics cards.

69 Systems with video processors (3/3) Graphics processor is controlled via an instruction queue. All data transferred between host memory and coprocessor memory must go through both CPU Unimplemented algorithms may be slow, since host machine has no direct access to the frame buffer. May be considerable communication overhead if coprocessor instruction registers are not memory mapped.

70 Example: Voodoo Voodoo chipset manufactured by 3Dfx, Inc. 3D-only graphics chipset. Card manufacturers would build cards around Voodoo chip Came out in probably first consumer-level 3D accelerator. Combined hardware (Voodoo chip) and software (Direct3D/OpenGL/Glide) solution.

71 Voodoo hardware Features: " Filled 45 Million pixels/s; 1 million triangles/s " Hardware z buffer (16-bit). " Perspective corrected Gouraud-shaded texture-mapped triangles done in hardware. " Alpha blending (allows transparency) Software provided polygons, normals and textures, and did all the geometry (modelling, viewing) and lighting itself.

72 Example: GeForce 256 Released in One chip solution; 2D and 3D support. 2D includes MPEG-2 (DVD) decoder. RAM from 32MB-128MB GeForce GPU (graphics processing unit) has 23 million transistors... more than Intel PIII.

73 Hardware features (1/2) Still unique for PC board in that it does transformation and lighting in hardware. Means more CPU for game physics etc. 4-stage pipeline: " Transformation " Lighting " Triangle setup & clipping " Rasterisation 4 pipelines (16 units).

74 Hardware features (2/2) Hardware support for: " Phong shaded texture-mapped polygons " Bump mapping " Cube environment mapping 480 Mpixels/s, 15 million polygon/s. Extremely fast. Some very nice white papers on T & L and cube enviromapping.

75 GeForce 3 57 million transistor chip (Pentium 4 is ~40 million) Released in April Programmability means it's really another computer within your computer. Graphics hardware is moving at 3x Moore's Law.

76 Render farms Closely related to Beowulf clusters Idea: Use many tightly- coupled off-the-shelf machines to do rendering Problem: Dividing the work But sometimes easy, e.g. one frame per machine Example: Titanic water effects used cluster of about 160 Alphas running Linux/NT.