DDA - Digital Differential Analyzer

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 • DDA stands for Digital Differential Analyzer.

• getpixel and putpixel are two functions which we will use everytime in our program.

• Declarations:

1) int getpixel(int x, int y);

2) void putpixel(int x, int y, int color);

• Function getpixel returns the integer value  of the pixel color present at point(x, y).

• Function putpixel plots a pixel at a point(x, y) of the specified color.

•Steps: 

1) slope of line(m): y2-y1/x2-x1 

** m= dy/dx = y2-y1/x2-x1 

2) dy= m*dx 

3) dx= dy/m 

• Above three formulas are very important in order to understand DDA Algorithm.

• Algorithm:

1) Start 

2) User Input: Coordinate x1, y1 and x2, y2 for line.

3) Find slope m 

4) Find dx 

5) Find dy  with the help of above formula.

6) Check: dx >=dy if yes,

 dx = 1

 x1= x1 + dx;

 y1 = y1 + m1 * dx;

7) else: 

    dy1  = 1;

 x1   = x1 +(dy1/m1);

y1   = y1 + dy1;

8)putpixel(x1,y1,color_name);

9) We will continue the steps from 4 to 8 till x1==x2 and y1==y2

• Example: 

If x1 and y1= (1,1)

    X2 and y1= (4,3)

Then: 

x1=1

y1=1

x2= 4

y2=3

dx = 4 - 1 = 3

dy = 3 - 1= 2

 m = dy/dx

      = 2/3

      = 0.67

1) Check dx>=dy 

dx= 1

 x1= x1 +dx 

     = 1 + 1

x1= 2

y1= y1 + dy 

    = 1 + m*dx    

// dy= m*dx 

    = 1 + 0.67*1

    = 1.67

x1= 2 and y1= 1.67

Find 

dx= x2-x1= 4-2= 2

dy= y2-y1= 3-1= 2.  // 1.67 as int

2) Check  dx>=dy    yes,

dx= 1

x1= x1 +dx  

     = 2 + 1.  

// x1 = 2 previous value

x1= 3

y1= y1 + dy 

    = 1.67 + m*dx 

    = 1.67 + 0.67* 1

y1= 2.34

x1= 3 and y1= 2

Find 

dx= x2-x1= 4 -3= 1

dy= y2-y1= 3 -2= 1

3) Check  dx>=dy    yes,

 dx= 1

 x1= x1 +dx   

      =3 + 1.  

 x1= 4

 y1= y1 + dy 

     = 2.34+ m*dx 

      = 2.34 + 0.67* 1

  y1= 3.01

x1= 4 and y1= 3

• Hence we can stop here though we got the end points.


• Refer the program at this link: 

https://github.com/Rinky6767/Computer-Graphics/blob/main/DDA%20line%20drawing%20program


Output: 


*You can leave a comment if you have doubt in it.







     



          












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