PTIK UNNES. Lecture 02. Conceptual Model for Computer Graphics and Graphics Hardware Issues

Transcription

1 E KOMPUTER GRAFIK E PRAKTIK KOMPUTER GRAFIK PTIK UNNES Lecture 02 Conceptual Model for Computer Graphics and Graphics Hardware Issues 2014

2 Learning Objectives After carefully listening this lecture, students will be able to do the following : explain each of the main components of computer graphics conceptual model show the requirements of the graphics system describe the major input/output devices required by the graphics system

3 Lecture Outlines Conceptual model for computer graphics Overview of graphics system and graphics system H/W such as CRT and other input devices

4 Conceptual Model for CG Application model : a database of description and properties. Description of primitives that defines the shape of the objects Object attributes like line styles, color, texture that defines the look of the objects Connectivity relations and positioning data that defines how component fit together Textual, numeric data (equations, formulas, etc) and procedures often included in the model

5 Conceptual Model for CG Application program : a collection of output plotting routines based on 2D or 3D geometry of the object to be displayed. View transform : specifies what part of the world scene is to be displayed and convert those points into view coordinates points. Maps data to device coordinates : all geometric and non geometric details in the data structure are converted and passed to graphic system (e.g. objects are scan-converted into pixels and the frame buffer displayed.

6 Conceptual Model for CG Graphics System High level language interface to graphical devices. Intended for development of portable code. Standard graphical systems include Graphical Kernel System (GKS), GKS+ Programmers Hierarchical Interactive Graphics System (PHIGS), PHIGS+ OpenGL, DirectX, QuickDraw 3D, VRML, Open Inventor, X-Windows.

7 Conceptual Model for CG Requirements of Graphical Systems Portability Device Independence (concept of a logical device) language Independence (language bindings for graphical systems) Computer Independence (trade-off between standard hardware and high performance hardware). Programmer Independence

8 Graphics Display H/W Raster graphics architecture with display processor cut down the load of the CPU Performs scan line conversion and raster operations CPU and graphics processor communicate via queuing system allowing CPU to get on with other jobs while graphics processor handles the display

9 Frame Buffer Frame Buffer : A memory array in which the computer stores an image - On most computers, separate memory bank from main memory - A true-color (24-bit or 32-bit) frame buffer stores one byte each for red, green, and blue. Each pixel can thus be one of 2 24 colors

10 Frame Buffer An indexed-color (8-bit or pseudo color) frame buffer stores one byte per pixel (also: GIF image format) This byte indexes into a color map or lookup table

11 Video Controller Layout Raster scan generator is activated each time the screen is refreshed. It does two things : - controls the X and Y addresses registers, giving the x and y coordinates of the pixel. - generates the correct vertical and horizontal deflection The X and Y address registers combined by the linear address calculator access the relevant part of memory for the given pixel

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

13 Display Devices : CRT s

14 Display Devices : CRT s A CRT can operate as a random scan (vector display) or a raster scan (raster display) Vector Display Electron beam directed only at parts of screen containing the picture. Early computer displays : basically an oscilloscope Control X, Y with vertical/horizontal plate Often used intensity as Z Raster Display Electron beam scans whole screen, with the intensity set to ON or OFF to produce the picture. Picture composed of a set of points (pixels). Screen divided into scan lines Horizontal and vertical retrace of beam. Interlaced and non-interlaced devices.

15 Display Devices : CRT s Raster Displays Frame must be refreshed to draw new images Raster : A rectangular array of points or dots Pixel : One dot or picture element of the raster Scanline : A row of pixels Rasterize : find the set of pixels corresponding to a 2D shape (line, circle, polygon) As new pixels are struck by electron beam, others are decaying Electron beam must hit all pixels frequently to eliminate flicker Critical fusion frequency Typically 60 times/sec Varies with intensity, individuals, phosphor persistence, lighting...

16 Color CRT s Color CRTs have Three electron guns A metal shadow mask to differentiate the beams

17 Display Devices : Raster CRT s Raster CRT pros: Allows solids, not just wireframes 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)

18 Display Devices : LCD s 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.

19 Display Devices : LCD s 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

20 Display Devices : 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

21 Display Devices : Plasma Plasma Display Panel Pros Large viewing angle Good for large-format displays Fairly bright Cons Expensive Large pixels (~1 mm versus ~0.2 mm) Phosphors gradually deplete Less bright than CRTs, using more power

22 Input Devices : Physical Input Physical Input Devices: Trackballs and Joysticks. Analog input controlled by transducers Convert user s movement into changes in voltage/amperage by varying the resistance of the circuit Mouse Good for choosing, positioning, and drawing Digital version like optical mouse and acoustical mouse are also available Keyboard Good for entering alpha numeric data Encode keyboard characters using ASCII Light pen The tip of the light pen is light sensitive, activated during contact on the screen Touch screen, Graphics Tablet, Image Digitizer, etc

23 Input Devices : Logical Input Logical Input Devices: Locator. Provide coordinate information 2D or 3D Button Used to select and activate events controlling the interactive flow Keyboard Conceptually and functionally be considered as a collection of buttons Valuator (slider) Provide a single value, generally a real number Pick Identifies or select objects or sub pictures within the displayed picture