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GRAPHICS DEVICES AND

OUTPUT PRIMITIVESJ.J. ADRI JOVIN

Assistant Professor

Department of Information TechnologySri Ramakrishna Institute of Technology

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Raster Scan Displays

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Random Scan Displays

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Architecture

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Color CRT Monitor

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Flat Panel Displays

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Input Devices

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Trackball

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Space ball

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Joystick

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Image Scanner

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Touch Panel

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Light Pen

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Points and Lines

setpixel(x,y) load a specified color point in

the location specified by x and y

getpixel(x,y)retrieve the current frame

buffer intensity

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Line drawing algorithms

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cxmy .

12

12

xx

yym

11 xmyc

m

yx

xmy

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DDA Algorithm

Digital Differential Analyzer

Consider positive slope and the slope is less

than or equal to 1.

We sample at unit x interval

For lines with positive slope, greater than 1,the roles of x and y are reversed

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myy kk 1

mxx kk

11

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DDA Algorithm (Contd..)

If the process start from right end point, we

have

Therefore

Similarly, for slope greater than 1,

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1x

myy kk 1

mxx kk 11

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DDA Algorithm (Contd..)

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Bresenham Line Drawing Algorithm

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1. Input the two line endpoints and store the left endpoint in ),( 00 yx .

2. Load ),( 00 yx into the frame buffer; that is, plot the first point.

3. Calculate constants ,2,, yyx and xy 22 and obtain the starting value for the

decision parameter as

xyp 20

4. At each kx ,along the line, starting at 0k ,perform the following test. If 0kp , the

next point to plot is ),1( kk yx and

ypp kk 21

Otherwise, the next point to plot is )1,1( kk yx and

xypp kk 221 5. Repeat step 4 x times.