DDA Algorithm in Computer Graphics

DDA algorithm scans and converts lines with acceptable approximation in sufficiently less time. Assume that a line is to be rasterized between given endpoints (x_start, y_start) and (x_end, y_end).

Now let us consider the equation of the line as:
y=mx+c

where m represents the slope of the line and c is the y-intercept. This slope can be expressed as-

m= (y_end – y_start)/(x_end – y_start)

DDA Algorithm:

1. Read the line endpoints (x₁, y₁) and (x₂, y₂)
2. Δx=| x₂ – x₁ |
Δy=| y₂ – y₁ |
3. if(Δx≥ Δy) then
length=Δx
else
length=Δy
4. Select the raster unit,
Δx= (x₂ – x₁)/length
Δy= (y₂ – y₁)/length
5. x= x+0.5*sign(Δx)
y= y+0.5*sign(Δy)
Sign function algorithm work in all quotient. It returns (-1,0) depending on whether it agreement is
< 0, =0, > 0 respectively.
6. Now plot the points i=1,
while(i≤ length)
{
Plot(integer(x), integer(y))
x=x+Δx
y=y+Δy
i=i+1
}
7. STOP