4.4.1 Example

The following example renders three Koch curves that form sort of a ``snowflake'' shape. Each curve is created by a procedural which just uses a regular Python function as subdivide function. No RIB is generated by this example.
It is possible to create the same image using the generic ri module, but the procedural would have to be written as a separate Python script that is invoked using the ``RunProgram'' procedural. The code would actually be longer because you would have to encode/decode the parameters of the procedural as strings whereas this example directly passes vector objects around.

# Render a Koch snowflake as procedurals

import cgkit.cri
from cgkit.cgtypes import *

def bound(A, E):
    """Compute the bounding box of one segment."""
    eps = 0.03
    dv = E-A
    n = vec3(-dv.y, dv.x, 0)
    C = 0.5*(A+E) + 0.2887*n
    xx = [A.x, C.x, E.x]
    yy = [A.y, C.y, E.y]
    bound = [min(xx)-eps, max(xx)+eps, min(yy)-eps, max(yy)+eps, -0.001, 0.001]
    return bound

def subdiv(data, detail):
    """Subdivide function."""
    A,E = data
    dv = E-A
    if dv.length()<0.005:
        RiCurves(RI_LINEAR, [2], RI_NONPERIODIC, P=[A,E], constantwidth=0.003)
    else:
        t = 1.0/3
        B = (1.0-t)*A + t*E
        D = (1.0-t)*E + t*A
        n = vec3(-dv.y, dv.x, 0)
        C = 0.5*(A+E) + 0.2887*n
        RiProcedural((A,B), bound(A,B), subdiv)
        RiProcedural((B,C), bound(B,C), subdiv)
        RiProcedural((C,D), bound(C,D), subdiv)
        RiProcedural((D,E), bound(D,E), subdiv)

# Load the RenderMan API.
# Replace the library name with whatever renderer you want to use.
ri = cgkit.cri.loadRI("3delight")
cgkit.cri.importRINames(ri, globals())

RiBegin(RI_NULL)
RiFormat(1024,768,1)
RiDisplay("koch.tif", RI_FRAMEBUFFER, RI_RGB)
RiPixelSamples(3,3)
RiProjection(RI_ORTHOGRAPHIC)
RiScale(vec3(0.8))
RiTranslate(0,0.55,5)
RiWorldBegin()
RiSurface("constant")
RiColor((1,1,1))
RiPatch(RI_BILINEAR, P=[-2,2,1, 2,2,1, -2,-2,1, 2,-2,1])
RiColor((0,0,0))
RiProcedural((vec3(-1,0,0),vec3(1,0,0)), [-2,2, -2,2, -0.01,0.01], subdiv)
RiProcedural((vec3(0,-1.732,0),vec3(-1,0,0)), [-2,2, -2,2, -0.01,0.01], subdiv)
RiProcedural((vec3(1,0,0), vec3(0,-1.732,0)), [-2,2, -2,2, -0.01,0.01], subdiv)
RiWorldEnd()
RiEnd()