Shaders and Texturing - An Introduction to Computer Graphics for Artists - page 208

Fig. 11.32 Maps used as the basis for a blend map solution (Image courtesy of Lennart Hillen)

For purposes of organization, tiles may be divided into the following categories:

• One material

• Two or more materials blended

• Straight

• Corner

• Angle

The fewer materials represented in each tile, the more fl exible the tile will be. For
borders between irregularly shaped materials like grass and mud, blend tiles are
needed. A blend tile defi nes the edge between two materials, whether hard or soft,
and disrupts the straight edged pattern made by polygon borders.
When you are happy with your tile set and the geometry it will be mapped to, it
is time to apply the tiles. Doing so can be time-consuming, depending on the num-
ber of individual quads that must be mapped. Just like laying tile in a bathroom, the
more tiles there are, the longer it will take. For terrain objects, you may want to
introduce some randomness to speed up the process, but within carefully defi ned
limits. One way to do this is to trace out border areas that cannot be random, and
then fi ll the interior of each border with the same tile. After assigning the maps, you
can randomly select polygons and modify the orientation of their UVs to adjust the
overall mapping. Depending on the tilability of your maps, this method can work
for large sections of terrain.

11.5.6.3 Blend Maps

Blend maps are also used on large terrain objects. These are texture maps that spec-
ify how to blend between different textures, such as between dirt and grass
(Figs. 11.32 and 11.33 ). These maps allow separate tiled textures to interrupt each
other to create unique patterns within them to disguise the tiling effect (Fig. 11.34 ).
This method can be more quickly executed than making a good tile set but because
it is dependent on tiling, it works best with complex terrain models and high res
displacement and normal maps to interrupt the tiling effect.