 SURFACE UP blends between two parameters by calculating the angle between the normal
for each point of a 3D surface and the up vector.
How Does It Work?
SURFACE UP calculates a blend between two colors, two percent values, or two distinct bump patterns.
It does this by determining the angle between the surface normal for each point and the up vector. Although it varies with the platform, in darktree we define the "up" vector as the traditional positive Y axis.
The Pitch and Heading parameters change the position of the up vector. Giving a new value to Pitch will
move the blend further up or down on the texture. Changing the Heading will move the blend to the left or right.
Hints!
SURFACE UP is particularly good for adding moss, dust, or snow to the top of a surface. Since powders
like snow can only stick to the flatter areas of a surface, SURFACE UP is ideal for letting you dust the top only. Figure F2 below shows a snow on rock example.
The SURFACE UP component is not restricted to up direction effects. Using the Heading and Pitch
controls, you can orient this component in any direction. For example, in northern forests, moss tends to grow on the north side of trees. You could use SURFACE UP to achieve this effect. Another example
is a space craft entering the atmosphere. The sides of the vehicle that are facing forward will get hot and glow wile the side that faces away will be cooler. Orienting surface up in the reentry direction will allow
you to assign a "hot" shader to the leading edges.
Note: Using a bitmap of a SURFACE UP DarkTree to texture a 3D model will not be accurate since it is pre-rendered and cannot conform to separately designed geometry.
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