RenderMan Shading Language

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RenderManShading Language

• Daniel Scherzer
• Vienna University of Technology

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abstraction
SW
RenderMan
Real-Time Shading Languages
OpenGL 2.0
OpenGL
HW Shader
time
HW
1987
2002
1998
1992
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What is RenderMan (1)?
MonstersInc by Pixar
Entropy image contest winner by Claude Schitter
A Bugs Life by Pixar
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What is RenderMan (2)?

• created and defined by Pixar at 1987
• a postscript for 3D
• a Scene Description Language
• not a modeling program
• not a rendering program
• interface between modeling and rendering
• a standard not a product
• implementations Photorealistic RenderMan, BMRT,
  Entropy

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RenderMan Structure

• RIB (RenderMan Interface Bytestream)
• ASCII, binary
• API
• function calls
• Shading Language
• C-style with specialized datatypes (vector,
  color) and functions (reflect, normalize)

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RIB Example

• Display "RenderMan" "framebuffer" "rgb"
• Format 256 192 1
• WorldBegin
• Surface "constant"
• Polygon "P" 0.5 0.5 0.5 0.5 -0.5 0.5 -0.5 -0.5
  0.5 -0.5 0.5 0.5
• WorldEnd

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RIB Example

• Display "RenderMan" "framebuffer" "rgb"
• Format 256 192 1
• WorldBegin
• Surface "constant"
• Polygon "P" 0.5 0.5 0.5 0.5 -0.5 0.5 -0.5 -0.5
  0.5 -0.5 0.5 0.5
• WorldEnd

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API Example

• include ltri.hgt
• RtPoint Square4 .5,.5,.5, .5,-.5,.5,
  -.5,-.5,.5, -.5,.5,.5
• main(void)
• RiBegin(RI_NULL) / Start the renderer /
• RiDisplay("RenderMan", RI_FRAMEBUFFER,
  "rgb", RI_NULL)
• RiFormat((RtInt) 256, (RtInt) 192, 1.0)
• RiWorldBegin()
• RiSurface("constant", RI_NULL)
• RiPolygon( (RtInt) 4, / Declare
  the square /
• RI_P, (RtPointer) Square,
  RI_NULL)
• RiWorldEnd()
• RiEnd() / Clean up /

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Shading Language Example

• surface clouds(float vfreq .8 )
• float sum
• float i
• color white color(1.0, 1.0, 1.0)
• point Psh transform("shader", P)
• sum 0
• freq vfreq
• for (i 0 i lt 6 i i 1)
• sum sum 1/freq abs(.5 - noise(freq
  Psh))
• freq 2 freq
• Ci mix(Cs, white, sum4.0)
• Oi 1.0 / Always make the
  surface opaque /

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Shading Language Example

• surface clouds(float vfreq .8 )
• float sum
• float i
• color white color(1.0, 1.0, 1.0)
• point Psh transform("shader", P)
• sum 0
• freq vfreq
• for (i 0 i lt 6 i i 1)
• sum sum 1/freq abs(.5 - noise(freq
  Psh))
• freq 2 freq
• Ci mix(Cs, white, sum4.0)
• Oi 1.0 / Always make the
  surface opaque /

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Shading Language Example

• surface clouds(float vfreq .8 )
• float sum
• float i
• color white color(1.0, 1.0, 1.0)
• point Psh transform("shader", P)
• sum 0
• freq vfreq
• for (i 0 i lt 6 i i 1)
• sum sum 1/freq abs(.5 - noise(freq
  Psh))
• freq 2 freq
• Ci mix(Cs, white, sum4.0)
• Oi 1.0 / Always make the
  surface opaque /

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Shading Language Example

• surface clouds(float vfreq .8 )
• float sum
• float i
• color white color(1.0, 1.0, 1.0)
• point Psh transform("shader", P)
• sum 0
• freq vfreq
• for (i 0 i lt 6 i i 1)
• sum sum 1/freq abs(.5 - noise(freq
  Psh))
• freq 2 freq
• Ci mix(Cs, white, sum4.0)
• Oi 1.0 / Always make the
  surface opaque /

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Shading Language Example

• surface clouds(float Kd.8, Ka.2 )
• float sum
• float i, freq
• color white color(1.0, 1.0, 1.0)
• point Psh transform("shader", P)
• sum 0
• freq 4.0
• for (i 0 i lt 6 i i 1)
• sum sum 1/freq abs(.5 - noise(freq
  Psh))
• freq 2 freq
• Ci mix(Cs, white, sum4.0)
• Oi 1.0 / Always make the
  surface opaque /

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RIB with Shader Example

• Display "RenderMan" "framebuffer" "rgb"
• Format 256 192 1
• WorldBegin
• Surface "clouds"
• Polygon "P" 0.5 0.5 0.5 0.5 -0.5 0.5 -0.5 -0.5
  0.5 -0.5 0.5 0.5
• WorldEnd

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Result
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RenderMan Structur (2)
RIB File
Rman Geom Code
Rman Program
cc
render Program
Rman Shader .sl
shader
Byte-code Shader .slo
Image File
txmake
TIFF image
Rman texture
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RenderMan Shading Language (1)

• C-style
• C operators cross-product scalar-product
• datatypes float, vector, matrix, color
• functions geometry functions (length, distance,
  normalize, reflect), math functions (clamp,
  random)
• no pointers
• implicit parameters and results (P, N, u, v,
  time, Cs, Os, Ci, Oi)
• implicit execution

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RenderMan Shading Language (2)

• Shader types
• surface
• light
• volume
• displacement
• transformation
• image

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RenderMan Shading Language (3)

• uniform vs. varying
• uniform means that the parameter is the same
  across surface
• more efficient
• default
• varying variables can be attached to vertices
• interpolated across surface

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Surface Shader Example

• surface plastic( float Ks .5, Kd .5,
• Ka 1, roughness .1
• color specularcolor 1 )
• normal Nf faceforward(normalize(N), I )
• vector V normalize(-I)
• Oi Os
• Ci Os( Cs (Kaambient() Kddiffuse(Nf))
• specularcolor Ks specular(Nf,V,roughness)
  )

uniform varying
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Light Shader Example

• light
• pointlight(
• float intensity 1
• color lightcolor 1
• point from point "camera" (0,0,0) )
• illuminate( from )
• Cl intensity lightcolor / L.L

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Results
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Results
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Results