Lecture 1 Computer Graphics Hardware

Transcription

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

2 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 CP411 Computer Graphics 2

3 Electron Gun 1. 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. CP411 Computer Graphics 3

4 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 CP411 Computer Graphics 4

5 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 CP411 Computer Graphics 5

6 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 6

7 Example: How to draw a character? 7

8 Hardware for raster display system Figure 2-17 Architecture of a raster system with a fixed portion of the system memory reserved for the frame buffer. 8

9 Draw a picture into frame buffer Often done by GPU GPU does more 9

10 Figure 2-20 Architecture of a raster-graphics system with a display processor. 10

11 Definitions of 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, e.g. RGB The number of bits is called color depth The image represented in this way is called bitmap or pixmap 11

12 Frame Buffer The frame buffer is a part of RAM in a computer allocated to hold the graphics information for one frame of image. Frame buffer size determines the maximum resolution and color depth of the image FB size = resolution color depth, e.g. 640X480X8 bit = bit = Byte Frame buffer can be a part of main memory, or on the video card Image is generated by CPU/GPU and write (or load) into frame buffer Image in frame buffer is read out by video controller to display on the screen CP411 Computer Graphics 12

13 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? CP411 Computer Graphics 13

14 Interlaced Scanning and Progressive scanning CP411 Computer Graphics 14

15 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 / ps All efforts are made to draw more, fast, good and cost less 15

16 Video Graphics Arrays (VGA) Graphics hardware standard 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) MHz or MHz master clock Maximum of 720 horizontal pixels Maximum of 480 lines Refresh rates at up to 70 Hz Vertical Blanking interrupt 16

17 VGA timing information Horizontal timing 17

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19 TV signal -> Frame Buffer VGA controller 19

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21 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 CP411 Computer Graphics 21

22 Other components Video BIOS (firmware) RAMDAC Output connectors Motherboard interface PCI: 32 bit, 33 MHz. Replaced the previous buses from PCI allowed dynamic connectivity between devices, avoiding the jumpers manual adjustments AGP: First used in Dedicated to graphics bus, 32 bits, 66 MHz. PCI-Express: Point to point interface, released in In 2006 provided double data transfer rate of AGP, 32 bits, 133 MHz CP411 Computer Graphics 22

23 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 and GPU communicate over the PCI bus. CPU sends data to the GPU GPU processes data and store image data in frame buffer CP411 Computer Graphics 23

24 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 Major manufactures: Intel, AMD/ATI, Nvidia, 3DLabs, SiS Inc. Abit Ltd, AsusTek CP411 Computer Graphics 24

25 GPU has more computing power GPU has 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 CP411 Computer Graphics 25

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27 A logical block diagram of the R600 GPU, Source: AMD. CP411 Computer Graphics 27

28 A closer look at AMD's CPU/GPU Fusion CP411 Computer Graphics 28

29 Questions for next class 1. What are the two types of displays for graphics? 2. Give examples of two types of printing devices using the two types of display methods 3. How would you store images for the different types of displays? 29

30 Questions for next class 1. A raster system has a resolution of 1280 by 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 10 5 bits can be transferred? 3. A raster system has a resolution of 1280 by 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? CP411 Computer Graphics 30