Scene layout comparison.
Version 3.9
Version 3.9.1.0
September 28 2010
This shader package provides a solution to a common problem with large number of scene elements which use the same material or shading graph just with slightly different parameters per element. Instead of creating a separate copy of the whole material for each scene element that would require the adjustment of a single parameter, the material parameters are dynamically driven by attributes defined on the current scene element. This way, the material definition, or the complex shading graph, can be created once, and customizations of the shading properties are done at the object or instance level of the scene. The following picture shows the general difference in scene layout.
The standard technique with individual materials for each object works well for scenes where many different materials are used for the majority of scene elements. The explicitly established dependencies also imply least runtime overhead. On the other hand, the user data solution allows to model the material once but still react to custom override parameters attached to the scene object. The values of the parameters are looked up dynamically during rendering which incurs additional execution time. However, the shaders ensure this is done just once per object per frame to keep the overhead small and usually negligible.
This package offers both components to implement such a workflow:
declare data
"mib_data_bool"
(
string "name",
boolean "value"
)
end declare
declare data
"mib_data_int"
(
string "name",
integer "value"
)
end declare
declare data
"mib_data_scalar"
(
string "name",
scalar "value"
)
end declare
declare data
"mib_data_vector"
(
string "name",
vector "value"
)
end declare
declare data
"mib_data_color"
(
string "name",
color "value"
)
end declare
declare data
"mib_data_string"
(
string "name",
string "value"
)
end declare
declare data
"mib_data_texture"
(
string "name",
color texture "value"
)
end declare
declare data
"mib_data_shader"
(
string "name",
shader "value"
)
end declare
declare data
"mib_data_bool_array"
(
array string "names",
array boolean "values"
)
end declare
declare data
"mib_data_int_array"
(
array string "names",
array integer "values"
)
end declare
declare data
"mib_data_scalar_array"
(
array string "names",
array scalar "values"
)
end declare
declare data
"mib_data_vector_array"
(
array string "names",
array vector "values"
)
end declare
declare data
"mib_data_color_array"
(
array string "names",
array color "values"
)
end declare
declare data
"mib_data_string_array"
(
array string "names",
array string "values"
)
end declare
declare data
"mib_data_texture_array"
(
array string "names",
array color texture "values"
)
end declare
declare data
"mib_data_shader_array"
(
array string "names",
array shader "values"
)
end declare
declare shader
boolean
"mib_data_get_bool"
(
string "name",
boolean "default"
)
end declare
declare shader
integer
"mib_data_get_int"
(
string "name",
integer "default"
)
end declare
declare shader
scalar
"mib_data_get_scalar"
(
string "name",
scalar "default"
)
end declare
declare shader
vector
"mib_data_get_vector"
(
string "name",
vector "default"
)
end declare
declare shader
color
"mib_data_get_color"
(
string "name",
color "default"
)
end declare
declare shader
string
"mib_data_get_string"
(
string "name",
string "default"
)
end declare
declare shader
color texture
"mib_data_get_texture"
(
string "name",
color texture "default"
)
end declare
declare shader
shader
"mib_data_get_shader"
(
string "name",
shader "default"
)
end declare
declare shader
boolean
"mib_data_get_shader_bool"
(
string "name",
boolean "default"
)
end declare
declare shader
integer
"mib_data_get_shader_int"
(
string "name",
integer "default"
)
end declare
declare shader
scalar
"mib_data_get_shader_scalar"
(
string "name",
shader "default"
)
end declare
declare shader
vector
"mib_data_get_shader_vector"
(
string "name",
vector "default"
)
end declare
declare shader
color
"mib_data_get_shader_color"
(
string "name",
shader "default"
)
end declare
The user data related shaders are contained in the userdata library. The declaration of the shaders and data blocks can be found in the file userdata.mi. To use the shaders, the declaration file must be included and the library linked:
link "userdata.so" $include "userdata.mi"
This is an excerpt of a simple scene. It has a mib_data_color user data block attached to the instance inst of an object obj. The material mat assigned to that object has a surface shader with one input parameter diffuse connected to a mib_data_get_color shader which looks up the named attribute on the object, or instance, to drive its value. If the attribute can not be found on the current object then the value of the default parameter of the shader is returned instead.
data "red_diffuse"
"mib_data_color" (
"name" "diffuse",
"value" 1.0 0.0 0.0 # red
)
object "obj"
tagged
data "red_diffuse"
# ...
end object
shader "get_diffuse"
"mib_data_get_color" (
"name" "diffuse"
"default" 1.0 1.0 1.0 # white
)
material "mat"
"mib_illum_lambert" (
"diffuse" = "get_diffuse"
)
end material
instance "inst"
"obj"
material "mat"
end instance