Computer Graphics Lecture 03 Graphics Systems Cont… Taqdees A. Siddiqi

 RASTER-SCAN SYSTEMS  RANDOM-SCAN SYSTEMS  GRAPHICS CARDS OR DISPLAY ADAPTORS  GRAPHICS SOFTWARE Graphics Systems Cont…

 In simple organization; frame buffer can be anywhere in the system memory  Video controller accesses the frame buffer to refresh the screen Raster-Scan Systems Architecture of a simple raster graphics system

 Video controller or display controller  Raster scan display processor Raster-Scan Systems

Video Controller Architecture of a raster system with a fixed portion of system memory reserved for the frame buffer.

Video Controller Memory Addresses Pixel Register Frame Buffer Raster Scan Generator Register XRegister Y Horizontal and Vertical Deflection Voltages Intensity Basic Video Controller Refresh Operations

Raster Scan Display Processor System Bus I/O Devices Display Processor Memory CPU Display Processor Frame Buffer Architecture of a raster graphics systems with a display processor Video Controller Monitor System Memory

Raster-Scan Characters Defined as a grid of pixel positions Defined as a curve outline

Random-Scan Systems Architecture of a simple random scan system

Graphics Card or Display Adaptors A video card is typically an adaptor, a removable expansion card in the PC. Thus, it can be replaced! A video display Adaptor which is the special printed circuit board that plugs into one of the several expansion slots present on the mother board of the computer. A video display Adaptor is referred to as a video card as well. The video card can also be an integral part of the system board; this is the case in certain brands of PCs and is always the case in laptops and clear preference for the replaceable video card in some PCs.

Graphics Card or Display Adaptors A number of display Adaptors are available with varying capabilities specially Intel systems support following Adaptors:  Monochrome Adaptor (MA)  Hercules Adaptor (HA)  Color Graphics Adaptor (CGA)  Enhanced Graphics Adaptor (EGA)  Multicolor Graphics Adaptor (MCGA)  Video Graphics Adaptor (VGA)  Super Video Graphics Adaptor (SVGA)  Extended Graphics Adaptor (XGA)

Monochrome Adaptor  Simplest and the first available Adaptor  Can display only text and that too in single color

Hercules Adaptor  Emulates the Monochrome Adaptor  Can also operate in a graphics mode

Color Graphics Adaptor  Can display text and graphics in more than one color  Text mode is supported with 25 rows by 80 columns  Two resolutions available: 320 * 200 with 4 colors from a palette of * 200 with 2 colors

Color Graphics Adaptor  One drawback is that it produces: Flicker Snow

Enhanced Graphics Adaptor  Introduced by IBM in 1984 as alternative to CGA  EGA could emulate all functions of CGA and MA  palette of 64 colors

Enhanced Graphics Adaptor  Designed to avoid: Snow Flicker  A serious limitation is that it supports only write operation and no read operations

Multicolor Graphics Adaptor  Designed to emulate the CGA  To maintain compatibility with all the CGA modes  Provides two new graphics modes 640 * 480 in 2 colors 320 * 200 in 256 colors

Video Graphics Adaptor  Supports all the display modes of MA, CGA, MCGA  Provides graphics mode 640 * 480 in 16 colors

Super Video Graphics Adaptor  SVGA refers to enhancements to the VGA  SVGA has different capabilities on different cards for example: 800 * 600 and 1024 * 768 Another may have same resolution but more colors  SVGA required different driver for different cards

Extended Graphics Adaptor  XGA evolved from the VGA provides: greater resolution More colors Much better performance  XGA has its own graphics processor and bus mastering  XGA offers 2 new modes: 640 * 480 with 16 bit colors 1024 * 768 with 8 bit colors

Video Card Supports the CPU The video card provides a support function for the CPU. It is a processor like the CPU. However it is especially designed to control screen images.

RAM on the Video Card  How much RAM? That is significant for color depth at the highest resolutions  Which type of RAM? This is significant for card speed

3D - lots of RAM  To support the demand for high quality 3D performance new cards are coming with a frame buffer of 16 or 32 MB RAM  They use the AGP interface for: better bandwidth better access to the main memory

VRAM Most cards use very fast editions of ordinary RAM (SDRAM or DDR) Some high end cards (like Matrox Millennium II) earlier used special VRAM (Video RAM) chips. In principle, a VRAM cell is made up of two ordinary RAM cells, which are "glued" together. Therefore, you use twice as much RAM than otherwise.

VRAM VRAM has features:  Costs twice  Double cell allows the video processor to simultaneously read old and write new data on the same RAM address  VRAM is capable of reading and writing simultaneously due to the dual port design.

UMA and DVMT  Unified memory architecture (UMA) was very slow  Shared Memory Buffer Architecture (SMBA)  DVMT, Dynamic Video Memory Technology, found on Intel chip set 810 and 815  DVMT integrates the graphics controller and uses part of the system RAM as frame buffer

The RAMDAC  All traditional graphics cards have a RAMDAC chip  RAMDAC converts the signals from digital to analog form

The RAMDAC The recommendation on a good RAMDAC go like this:  External chip not integrated in the VGA chip  Clock speed MHz

Heavy Data Transport  The original VGA cards were unintelligent  CPU had to make all necessary calculations to create the screen image  Screen image of 1024*768 in 16 bit color is a 1.5 MB bit map 1024 x 768 x 2 bytes refresh rate of 75 HZ Zaps the PC energy  Transfer went through the ISA bus (limited width)

Accelerator Cards  Appeared in the early nineties  Now all cards are accelerated and they are connected to the CPU through high speed buses like PCI and AGP.  No need to calculate and design the entire bit map from image to image  Built in algorithms for drawing lines, Windows, and other image elements

Accelerator Cards  The AGP bus is an expanded and improved version of the PCI bus - used for video cards only  Modern video cards made for 3D gaming use expensive high-end RAM to secure a sufficient bandwidth

Accelerator Cards A game in a resolution of 1280 x 1024 at 80 Hz may need to move 400 MB of data each second The calculation goes like this: 1280 X 1024 pixels x 32 bit (color depth) x 80 = 419,430,400 bytes = 409,600 kilobytes = 400 megabytes.

Graphics Card

Graphics Card

Graphics Libraries Graphics developers some time use 2D or 3D libraries to create graphics rapidly and efficiently. These developers include game developers, animators, designers etc. The following libraries are commonly used among developers:  FastGL  OpenGL  DirectX  Others

Advantages of Graphics Libraries These libraries help developers to create fast and optimized animations and also help to access features that are available on video hardware. Hardware manufacturers give support in hardware for libraries Famous manufacturers includes.. SIS, NVIDIA, ATI, INTEL etc.

Graphics Software There are lot of 2D and 3D software are available in the market. These software provide visual interface for creation of 2D and 3D animation/ models, image creation. These tools are under use of movie makers professional animators and designers. These tools are flash, maya, 3D studio max, adobe photo shop, corel draw, image viewer, paintbrush etc.

Computer Graphics Lecture 03 Graphics Systems Cont… Taqdees A. Siddiqi