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Lecture 1 Computer Graphics Hardware Basic graphics hardware Display devices Video controller Memory CPU System bus Graphics Hardware # 1 CG show

Lecture 1 Computer Graphics Hardware Basic graphics hardware –Display devices –Video controller –Memory –CPU –System bus Graphics Hardware # 1 CG show

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Page 1: Lecture 1 Computer Graphics Hardware Basic graphics hardware –Display devices –Video controller –Memory –CPU –System bus Graphics Hardware # 1 CG show

Lecture 1 Computer Graphics Hardware

• Basic graphics hardware– Display devices– Video controller– Memory– CPU– System bus

Graphics Hardware # 1

CG show

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Display Devices• Cathode Ray Tubes (CRTs)

– A common display device– Evacuated glass bottle– Extremely high voltage– Heating element (filament)– Electrons emit towards

anode focusing cylinder– Vertical and horizontal deflection plates– Beam strikes phosphor coating on front of tube

• CRT Overview

– CRT technology hasn’t changed much in 50 years– Early television technology

• high resolution • requires synchronization between video signal and electron beam vertical

sync pulse– Early computer displays

• avoided synchronization using ‘vector’ algorithm• flicker and refresh were problematic

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Electron Gun1. Contains a filament that, when heated,

emits a stream of electrons

2. Electrons are focused with an electromagnet into a sharp beam and directed to a specific point of the face of the picture tube

3. Deflection of electronic beam can be controlled with either electronic or magnetic fields. E.g. Two pairs of magnetic deflection coils mounted on the outside of the CRT envelope, to control the deflection in horizontal (x) and vertical (y) direction respectively

4. The front surface of the picture tube is coated with small phosphor dots

5. Phosphor emits light for a short period of time when hit by electronic beam.

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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 arrangement In-line electron gun arrangement

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Vector Displays

• Vector displays– Draw object by electron beam– Early computer displays: basically an oscilloscope– Control X,Y with vertical/horizontal plate voltage – Often used intensity as Z

• Advantages

• Disadvantages

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Vector Displays

• Vector displays demo http://graphics.lcs.mit.edu/classes/6.837/F98/Lecture1/Slide11.html

• Advantages

• Disadvantages

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Raster Displays• The screen is divided into lines, and

each lines has many dots. The beam scans each line, the beam intensity is creased at a light dot

– Raster: A rectangular array of points or dots

– Pixel: One dot or picture element of the raster

– Scan line: A row of pixels

– Resolution: number of pixels per scan line times the number of scan lines

e.g. 640 X 480, 1024 X 768

• Show Simulation

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How to draw a character?

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Figure 2-17 Architecture of a raster system with a fixed portion of the system memory reserved for the frame buffer.

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Draw a picture into framebuffer

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• Often done by GPU• GPU does more

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Figure 2-20 Architecture of a raster-graphics system with a display processor.

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Raster Displays• To paint the screen by synchronizing with the scanning pattern of

raster

– Raster pattern is stored in a special memory called frame buffer

– Each pixel corresponds to a memory location, which can be 1 bit, 8 bits, 16 bits, or 24 bits

– The value represent a color according to certain color model and coding scheme

– The number of bits is called color depth

– The image represented in this way is called bitmap or pixmap

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Frame buffer• The frame buffer is a part of RAM in a computer allocated to hold

the graphics information for one frame or picture.

• Frame buffer size determines the maximum resolution and color depth of the image

FB size = resolution × color depth,

e.g. 640X480X8 bit = 2457600 bit = 307200 Byte

• Frame buffer can be a part of main memory, but mostly it is on the video card

• Image is generated by CPU/GPU and loaded into frame buffer• Image in frame buffer is read out by video controller to display on

the screen.

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Frame, refreshment, frequency, scanning

• Frame must be “refreshed” to draw new images– As new pixels are struck by electron beam, others are decaying– Electron beam must hit all pixels frequently to eliminate flicker

• frequency– How many frames per second– Typically 60 frames/sec

• How to scan a frame?– Progressive scanning

• Scan one line after another

– Interlaced Scanning• Scan all odd lines one by one and then scan all even lines one by one• This method can reduce flicker, why?

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Interlaced Scanning and Progressive scanning

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The unbalance of load and read

• Video controller read frame buffer and display on monitor on a fixed frequency, e.g. 60 Hz, at high refresh rate.

• Generally it is slow to generate a graph and load into frame buffer – The complexity of a graph, CPU and GPU speed, algorithms, and

system status

• What could happen when load and read frame buffer speed not match? Solution ?

• Graph generating speed matters for real time animation or virtual reality. Real time animation needs 24 frames / psAll efforts are made to draw more, fast, good and cost less

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Video Graphics Arrays (VGA)

• Graphics Hardward introduced by IBM• Specifications:

– 256 KB Video RAM– 16-color and 256-color modes– 262,144-value color palette (6 bits each for red, green, and

blue)– 25.175 MHz or 28.322 MHz master clock– Maximum of 720 horizontal pixels– Maximum of 480 lines– Refresh rates at up to 70 Hz– Vertical Blanking interrupt

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VGA timing information• Horizontal timing

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TV signal -> Frame Buffer – VGA controller

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Video card

• A video card, also known as a graphics accelerator card, display adapter, or graphics card, is a PC hardware component whose function is to generate and output images to a display. It operates on similar principles as a sound card or other peripheral devices.

• Components– Graphics processing unit (GPU): a dedicated graphics

microprocessor optimized for floating point calculations which are fundamental to 3D graphics rendering.

• Video memory– DDR RAM, 128 MB to 2.0 GB, 400 MHz to 2.4 GHz.– Store program, data, and frame buffer

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Other components

• Video BIOS (firmware)• RAMDAC• Output connectors

• Motherboard interface– PCI: 32 bit, 33 MHz. Replaced the previous buses from 1993. PCI allowed

dynamic connectivity between devices, avoiding the jumpers manual adjustments

– AGP: First used in 1997. Dedicated to graphics bus, 32 bits, 66 MHz.

– PCI-Express: Point to point interface, released in 2004. In 2006 provided

double data transfer rate of AGP, 32 bits, 133 MHz

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GPU

1. GPU is a separate, self-contained computing device dedicated for graphics computing. GPU has its own processing units, and its own memory banks.

2. The CPU has a direct link to the computer's main memory.

3. The CPU and GPU communicate over the PCI bus. – CPU sends data to the GPU– GPU processes data and store image data

in frame buffer

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What GPU does?

• Dedicated to calculating the graphics functions such as drawing basic graphic primitives with lighting effects, object transformations, and 3D motions.

• The roles of CPU and GPU?– CPU is doing model computation – GPU is doing rendering computation (graphics pipe line)

• Major manufactures: Intel, AMD/ATI, Nvidia, 3DLabs, SiS Inc. Abit Ltd, AsusTek

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GPU has more special computing power

• GPU is a massively parallel architecture– Many problems map well to GPU-style computing– GPUs have large amount of arithmetic capability– Increasing amount of programmability in the pipeline

• Programmable GPU– New features map well to GPGPU– Unified shaders– Direct access to computing units in new APIs

• Challenge– How do we make the best use of GPU hardware?– Techniques, programming models, languages

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A logical block diagram of the R600 GPU, 2007. Source: AMD.

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A closer look at AMD's CPU/GPU Fusion

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Intel Larrabee

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Answer Questions1. A raster system has a resolution of 1280 by 1024. If the color depth

is 24 bits per pixel. What size frame buffer (in bytes) is needed for this system?

2. How long would it take to load a 640 by 480 frame buffer with 12 bits per pixel if 105 bits can be transferred?

3. A raster system has a resolution of 1280 by 1024. How many pixels in frame buffer needs to be accessed per second by a display controller that refreshes the screen at a rate of 60 frames per second?

4. How much time spent scanning across each row of pixels during screen refresh on a raster system with resolution 1280 by 1024 and a refresh rate 60 frame per second?

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