Practical Algorithms for 3D Computer Graphics, 2nd Edition

4.6. Image and texture mapping 137

the Floor function is given in figure 4.11

α

m

= (float)F loor(α)

β

m

= (float)F loor(β)

b

x

= ((truncate α

m

)(bitwise AND) 1)

b

y

= ((truncate β

m

)(bitwise AND) 1)

α

m

= α − α

m

β

m

= β − β

m

i f b

x

6= 0 {

i f b

y

6

= 0 {

α

m

= 1 − α

m

β

m

= 1 − β

m

}

e ls e {

α

m

= 1 − α

m

}

}

e ls e i f b

y

6

= 0 {

β

m

= 1 − β

m

}

Listing 4.13: Generating a mosaic repeat pattern for seamless image mapping.

The second issue is the rather d is continu ou s way of rounding the floating

point texture coordinates (X, Y ) to the integer address (i, j) (i = truncate(x)

and j = truncate(y)) u s ed to pick the color from the image. A better appr oach

is to use a bilinear (or high er order)