Tag Archives: Normal maps

Tangent space normal maps

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The built-in N AOV is in world space. So how to get a tangent-space N AOV?
Like this:

In brief, I read the N AOV, transform the normals from world to tangent space, and then map the normal values to the range 0.5, 1 (I used the range node here, but I could have used Add and Multiply to do the same thing).

Here’s the shader tree. You can save this in a .ass file and import it into Maya or whatever application you use. Then set up an AOV shader to write the custom Ntangent AOV

range
{
 name aiRange1
 input space_transform
 output_min 0.5
}

space_transform
{
 name space_transform
 input read_N_AOV
 type "normal"
 to "tangent"
 tangent 1 0 0
 normal 0 1 0
 normalize on
}

aov_read_rgb
{
 name read_N_AOV
 aov_name "N"
}

aov_write_rgb
{
 name defaultArnoldRenderOptions/aov_write_rgb_Ntangent
 aov_input aiRange1
 aov_name "Ntangent"
}

[MtoA] Normal mapping with mayaBump2d

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mayaBump2D has an RGB parameter for normal maps, and it’s named “normal_map”:

C:\solidangle\mtoadeploy\2015\bin>kick -l ..\shaders -info mayaBump2D
node:         mayaBump2D
type:         shader
output:       RGBA
parameters:   11
filename:     ..\shaders/mtoa_shaders.dll
version:      4.2.4.1

Type          Name                              Default
------------  --------------------------------  --------------------------------

FLOAT         bump_map                          0
FLOAT         bump_height                       1
RGB           normal_map                        0, 0, 1
BOOL          flip_r                            true
BOOL          flip_g                            true
BOOL          swap_tangents                     false
BOOL          use_derivatives                   true
BOOL          gamma_correct                     true
ENUM          use_as                            bump
RGBA          shader                            0, 0, 0, 1
STRING        name

In Maya, you don’t connect your normal map directly to mayaBump2D.normal_map. Instead, just connect the normal map alpha to the Bump Value
normal_map_mayaBump2D
and then change bump2d > 2d Bump Attributes > Use As to Object Space Normals or Tangent Space Normals.
mayaBump2D_Use_As
The Use As parameter controls how MtoA translates the shaders to Arnold. For example, if Use As is Object Space Normals, you get this:

mayaBump2D
{
 name bump2d1
 bump_map file1.a
 bump_height 1
 normal_map file1
 flip_r on
 flip_g on
 swap_tangents off
 use_derivatives on
 gamma_correct on
 use_as "object_normal"
 shader aiStandard1
}

MayaFile
{
 name file1
 ...
 filename "shaders_offest_normalmap.jpg"
 ...

Notice that file1 (the MayaFile node) is linked to mayaBump2D.normal_map.