Practical Algorithms for 3D Computer Graphics, 2nd Edition

4.9. Line drawing 157

∆x = x

2

− x

1

∆y = y

2

− y

1

δ = −∆x/2

set x = x

1

and y = y

1

draw pixel at (x, y) with color c

while x < x

2

do {

δ = δ + ∆y

i f δ ≥ 0 {

y = y + y

inc

δ = δ − ∆x

}

x = x + 1

draw pixel at (x, y) with color c

}

Listing 4.16: The basic integer differential line generator algorithm.

∆x = x

2

− x

1

∆y = y

2

− y

1

i f |∆x| > |∆y| {

i f ∆x < 0 {

swap x

2

↔ x

1

swap y

2

↔ y

1

}

i f y

2

> y

1

then y

inc

= 1

e ls e y

inc

= −1

Call the first octant algorithm

}

e ls e {

i f ∆y < 0 {

swap x

2

↔ x

1

swap y

2

↔ y

1

}

i f x

2

> x

1

then x

inc

= 1

e ls e x

inc

= −1

Call the second octant algorithm

}

Listing 4.17: Algorithm for the drawing of a n arbitrarily directed straight line in a

raster display.

are swapped, and ...