The RenderMan Interface - Paul Bourke

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onto a surface. Texture maps are used in many different ways: direct image mapping to change the surface’s color, transparency mapping, bump mapping for changing its normal vector, displacement mapping for modifying position, environment or reflection mapping for efficiently calculating global illumination, and shadow maps for simulating the presence of shadows. The RenderMan Interface is designed so that the information needed to specify a photorealistic image can be passed to different rendering programs compactly and efficiently. The interface itself is designed to drive different hardware devices, software implementations and rendering algorithms. Many types of rendering systems are accommodated by this interface, including z-buffer-based, scanline-based, ray tracing, terrain rendering, molecule or sphere rendering and the Reyes rendering architecture. In order to achieve this, the interface does not specify how a picture is rendered, but instead specifies what picture is desired. The interface is designed to be used by both batch-oriented and real-time interactive rendering systems. Real-time rendering is accommodated by ensuring that all the information needed to draw a particular geometric primitive is available when the primitive is defined. Both batch and real-time rendering is accommodated by making limited use of inquiry functions and call-backs. The RenderMan Interface is meant to be complete, but minimal, in its transfer of scene descriptions from modeling programs to rendering programs. The interface usually provides only a single way to communicate a parameter; it is expected that the modeling front end will provide other convenient variations. An example is color coordinate systems – the RenderMan Interface supports multiple-component color models because a rendering program intrinsically computes with an n-component color model. However, the Render- Man Interface does not support all color coordinate systems because there are so many and because they must normally be immediately converted to the color representation used by the rendering program. Another example is geometric primitives – the primitives defined by the RenderMan Interface are considered to be rendering primitives, not modeling primitives. The primitives were chosen either because special graphics algorithms or hardware is available to draw those primitives, or because they allow for a compact representation of a large database. The task of converting higher-level modeling primitives to rendering primitives must be done by the modeling program. The RenderMan Interface is not designed to be a complete three-dimensional interactive programming environment. Such an environment would include many capabilities not addressed in this interface. These include: 1) screen space or two-dimensional primitives such as annotation text, markers, and 2-D lines and curves, and 2) user-interface issues such as window systems, input devices, events, selecting, highlighting, and incremental redisplay. The RenderMan Interface is a collection of procedures to transfer the description of a scene to the rendering program. These procedures are described in Part I. A rendering program takes this input and produces an image. This image can be immediately displayed on a given display device or saved in an image file. The output image may contain color as well as coverage and depth information for postprocessing. Image files are also used to input texture maps. This document does not specify a ”standard format” for image files. The RenderMan Shading Language is a programming language for extending the predefined functionality of the RenderMan Interface. New materials and light sources can be 3
created using this language. This language is also used to specify volumetric attenuation, displacements, and simple image processing functions. All required shading functionality is also expressed in this language. A shading language is an essential part of a high-quality rendering program. No single material lighting equation can ever hope to model the complexity of all possible material models. The RenderMan Shading Language is described in Part II of this document. 1.1 Features and Capabilities The RenderMan Interface was designed in a top-down fashion by asking what information is needed to specify a scene in enough detail so that a photorealistic image can be created. Photorealistic image synthesis is quite challenging and many rendering programs cannot implement all of the features provided by the RenderMan Interface. This section describes which features are required and which are considered advanced, and therefore optional, capabilities. The set of required features is extensive in order that application writers and end-users may reasonably expect basic compatibility between, and a high level of performance from, all implementations of the RenderMan Interface. Advanced capabilities are optional only in situations where it is reasonable to expect that some rendering programs are algorithmically incapable of supporting that capability, or where the capability is so advanced that it is reasonable to expect that most rendering implementations will not be able to provide it. 1.1.1 Required features All rendering programs which implement the RenderMan Interface must implement the interface as specified in this document. Implementations which are provided as a linkable C library must provide entry points for all of the subroutines and functions, accepting the parameters as described in this specification. All of the predefined types, variables and constants (including the entire set of constant RtToken variables for the predefined string arguments to the various RenderMan Interface subroutines) must be provided. The C header file ri.h (see Appendix C, Language Binding Details) describes these data items. Implementations which are provided as prelinked standalone applications must accept as input the complete RenderMan Interface Bytestream (RIB). Such implementations may also provide a complete RenderMan Interface library as above, which contains subroutine stubs whose only function is to generate RIB. All rendering programs which implement the RenderMan Interface must: • provide the complete hierarchical graphics state, including the attribute and transformation stacks and the active light list. • perform orthographic and perspective viewing transformations. • perform depth-based hidden-surface elimination. • perform pixel filtering and antialiasing. 4
Page 1 and 2: The RenderMan Interface Version 3.2
Page 3 and 4: TABLE OF CONTENTS List of Figures L
Page 5 and 6: 12.1 Surface Shaders . . . . . . .
Page 7 and 8: Section I DIFFERENCES BETWEEN VERSI
Page 9 and 10: LIST OF TABLES 4.1 Camera Options .
Page 11 and 12: PREFACE This document is version 3.
Page 13: Section 1 INTRODUCTION The RenderMa
Page 17 and 18: Depth of Field The ability to simul
Page 19 and 20: typedef RtPointer typedef RtPointer
Page 21 and 22: RiContext (ctx1); ... There is no R
Page 23 and 24: Section 3 RELATIONSHIP TO THE RENDE
Page 25 and 26: through the interface. Any place wh
Page 27 and 28: RtContextHandle RiGetContext ( void
Page 29 and 30: RiWorldBegin (); ... RiColor (...);
Page 31 and 32: Camera Option Type Default Descript
Page 33 and 34: ottom top left right Screen Window
Page 35 and 36: EXAMPLE RiFrameAspectRatio (4.0/3.0
Page 37 and 38: not support the special projection
Page 39 and 40: This procedure sets the times at wh
Page 41 and 42: Output depth values are the camera-
Page 43 and 44: A particular renderer implementatio
Page 45 and 46: Renderers may additionally produce
Page 47 and 48: The number of color components, n,
Page 49 and 50: RiAttributeBegin () RiAttributeEnd
Page 51 and 52: RIB BINDING Color c0 c1... cn Color
Page 53 and 54: An area light source is defined by
Page 55 and 56: The sequencenumber is the integer l
Page 57 and 58: 4.2.5 Displacement shading The grap
Page 59 and 60: SEE ALSO RiExterior RiAtmosphere Ri
Page 61 and 62: Matte onoff EXAMPLE RiMatte (RI TRU
Page 63 and 64: object foo2 will be drawn when the
Page 65 and 66:
the exterior is the region adjacent
Page 67 and 68:
RiIdentity ( ); SEE ALSO RiTransfor
Page 69 and 70:
RiScale ( RtFloat sx, RtFloat sy, R
Page 71 and 72:
4.3.2 Transformation stack Transfor
Page 73 and 74:
Section 5 GEOMETRIC PRIMITIVES The
Page 75 and 76:
Information Name Type Class Floats
Page 77 and 78:
No checking is done by the RenderMa
Page 79 and 80:
5.2 Patches Patches can be either u
Page 81 and 82:
U V 0 1 2 3 12 13 14 15 4 5 6 7 8 9
Page 83 and 84:
10 x 7 Aperiodic Bezier Bicubic Pat
Page 85 and 86:
SEE ALSO 2 2 [ 0 0 1 1 ] 0 1 ”Pw
Page 87 and 88:
parameterlist is a list of token-ar
Page 89 and 90:
Requests a sphere defined by the fo
Page 91 and 92:
Hyperboloid 0 0 0 .5 0 0 270 ”Cs
Page 93 and 94:
z N z V point2 height U x x y 0 max
Page 95 and 96:
particle. If a primitive variable i
Page 97 and 98:
The code array is a sequence of mac
Page 99 and 100:
is an array of floats that define t
Page 101 and 102:
The helper program generates geomet
Page 103 and 104:
Procedural ”DynamicLoad” [ ”m
Page 105 and 106:
SolidBegin ( ”difference” ); So
Page 107 and 108:
Section 6 MOTION Some rendering pro
Page 109 and 110:
Transformations Geometry Shading Ri
Page 111 and 112:
channels (usually an RGB color) can
Page 113 and 114:
Image Forward Axis Up Axis Right Ax
Page 115 and 116:
ErrorHandler ”ignore” ErrorHand
Page 117 and 118:
Part II The RenderMan Shading Langu
Page 119 and 120:
spaces (such as CMYK or pseudocolor
Page 121 and 122:
transmit reflect transmit P E light
Page 123 and 124:
Section 10 RELATIONSHIP TO THE REND
Page 125 and 126:
Section 11 TYPES The Shading Langua
Page 127 and 128:
Coordinate System ”shader” ”c
Page 129 and 130:
As in C, individual array elements
Page 131 and 132:
Light Source E Vantage Point N L Il
Page 133 and 134:
Surface Element to Illuminate L N I
Page 135 and 136:
Name Type Storage Class Description
Page 137 and 138:
• conditional execution, • loop
Page 139 and 140:
This example integrates over a hemi
Page 141 and 142:
Shader instance variable values can
Page 143 and 144:
} return 2 * (vector noise(p)) - 1;
Page 145 and 146:
These functions compute power and i
Page 147 and 148:
The actual change in a variable is
Page 149 and 150:
Return a unit vector in the directi
Page 151 and 152:
Return surface normal given a point
Page 153 and 154:
diffuse returns the diffuse compone
Page 155 and 156:
prevent aliasing. If one set of tex
Page 157 and 158:
15.7.3 Shadow depth maps Shadow dep
Page 159 and 160:
These functions access the value of
Page 161 and 162:
The standard data names supported b
Page 163 and 164:
} Oi = sum; Ci = Cs * Oi * (Ka + Kd
Page 165 and 166:
path of the ray. The input Ci and O
Page 167 and 168:
A.2.3 Metal surface surface metal(
Page 169 and 170:
distantlight( float intensity = 1;
Page 171 and 172:
A.6 Imager Shaders A.6.1 Background
Page 173 and 174:
variable definitions ; variables va
Page 175 and 176:
triple sixteentuple arrayindex: [ e
Page 177 and 178:
Logical expressions have the value
Page 179 and 180:
typedef RtPointer RtContextHandle;
Page 181 and 182:
RiOptionV(RtToken name, RtInt n, Rt
Page 183 and 184:
RtInt n, RtToken tokens[], RtPointe
Page 185 and 186:
#define RIE_NOTATTRIBS ((RtInt)26)
Page 187 and 188:
Comments Any occurrence of the ’#
Page 189 and 190:
In the following sections the synta
Page 191 and 192:
C.2.2 Error handling There are two
Page 193 and 194:
adhandle badparamlist badripcode ba
Page 195 and 196:
v e r s i o n 212 # version 003 007
Page 197 and 198:
Using RIB File structuring conventi
Page 199 and 200:
Attribute Format PixelFilter Shadin
Page 201 and 202:
##Include filename This entry allow
Page 203 and 204:
D.2.1 RIB Entity File example ##Ren
Page 205 and 206:
Motion Blur Programmable Shading Di
Page 207 and 208:
} E.4 Gaussian Filter RtFloat RiGau
Page 209 and 210:
Appendix G RENDERMAN INTERFACE QUIC
Page 211 and 212:
Function RiOpacity (color) RiOption
Page 213 and 214:
Geometric Primitives (continued) Fu
Page 215 and 216:
Function abs(x) Math Functions Desc
Page 217 and 218:
Function area(P) calculatenormal(P)
Page 219 and 220:
Texture Mapping Functions Function
Page 221 and 222:
RiInterior 47 RiLightSource 42 RiMa
Page 223 and 224:
and uniform variables on an RiNuPat
Page 225 and 226:
Statement About Pixar’s Copyright
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The RenderMan Interface - Paul Bourke

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