renderman - writing renderman shaders (2)-. transforming tiles transforming texture coordinates has...
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RenderMan - Writing RenderMan Shaders (2)-
Transforming Tiles
• Transforming texture coordinates has an "inverse" effect on the appearance of the pattern– if you scale the texture coordinates by a
factor of 2, the frequency of the pattern will double and the pattern will appear twice as small
– positive translations will move the pattern up and to the left (the opposite direction)
– positive clockwise rotations will rotate the pattern counter-clockwise
Transforming Tiles• Rotating Tiles
– rotate2d(float x, y, angle, ox, oy, rx, ry)– Rotates a 2D point (x, y) clockwise by a specified angle (in r
adians) about an origin (ox, oy) and stores the resulting point in (rx, ry).
– To rotate the ‘cross’ shader, we replace the lines ss = repeat(s, freq);
tt = repeat(t, freq);
with rotate2d(s, t, radians(45), 0.5, 0.5, ss, tt);
ss = repeat(ss, freq); tt = repeat(tt, freq);
/* rotcross.sl */surfacerotcross(){
color surface_color, layer_color, surface_opac, layer_opac;float fuzz = 0.05; float ss, tt; float freq = 4;
/* background layer */surface_color = Cs; surface_opac = Os;
/* rotate 45 degrees and repeat pattern 'freq' times horizontally & vertically */
rotate2d(s, t, radians(45), 0.5, 0.5, ss, tt);ss = repeat(ss, freq); tt = repeat(tt, freq);
/* vertical bar layer */layer_color = color (0.1, 0.5, 0.1);layer_opac = pulse(0.35, 0.65, fuzz, ss);surface_color = blend(surface_color, layer_color, layer_opac);
/* horizontal bar layer */layer_color = color (0.1, 0.1, 0.3);layer_opac = pulse(0.35, 0.65, fuzz, tt);surface_color = blend(surface_color, layer_color, layer_opac);
/* output */Oi = surface_opac; Ci = surface_opac * surface_color;
}
Transforming Tiles
• Shifting Rows or Columns of Tiles– Alternating rows (or columns) of tiles can be stagger
ed by• using repeat, whichtile, and odd and/or even to determine i
f the current tile is in an odd or even row; and then• shifting or not shifting texture or coordinates appropriately.
– to shift even rows of a pattern by a 1/2 tile, you would add 0.5 to ss after it has been repeated. You still need to remember to mod ss with 1 so that it stays in the range 0 to 1.
row = whichtile(t, freq);if (even(row))
ss = mod(ss + 0.5, 1);
/* shiftedblocks.sl */surfaceshiftedblocks(){
color surface_color, layer_color;color layer_opac;float ss, tt;float row;float fuzz = 0.05;float freq = 4;surface_color = Cs;
/* shift even rows 1/2 tile */ss = repeat(s, freq);tt = repeat(t, freq);row = whichtile(t, freq);if (even(row))
ss = mod(ss + 0.5, 1);
/* squares */layer_color = color (0.3, 0.0, 0.3);layer_opac = intersection(pulse(0.35, 0.65, fuzz, ss),
pulse(0.35, 0.65, fuzz, tt));surface_color = blend(surface_color, layer_color, layer_opac);
/* output */Ci = surface_color;
}
Transforming Tiles
• Polar Coordinates– Polar coordinates are useful for generating radially sha
ped patterns (flowers, stars, etc.). The convenience function topolar2d converts a 2-D point in Cartesian coordinates to polar coordinates.
– topolar2d(float x, y, r, theta) • Transforms a 2-D point (x,y) in Cartesian coordinates to polar
coordinates expressed in terms of r (distance from the origin) and theta (the angle expressed in radians). theta will be in the range [-PI, PI].
Shape Generation
• Simple, geometric shapes can be made in the RenderMan Shading Language using smoothstep or pulse often with one of two shading language distance functions:– float distance(point p1, p2)– float ptlined(point a, b, p)
Shape Generation
• Rectangles– Rectangular shapes can be made by
intersecting (multiplying) a vertical pulse and a horizontal pulse.
– you can use intersection instead of the multiplication operator.
/* rect.sl */ surfacerect(){
color surface_color, layer_color;color layer_opac;float fuzz = 0.025;color red = color (1,0,0);float left, right, top, bottom;
surface_color = Cs;layer_color = red;left = 0.05; right = 0.75;
/* rectangle sides */top = 0.1; bottom = 0.7;layer_opac = pulse(left, right, fuzz, s)
* pulse(top, bottom, fuzz, t);surface_color
= blend(surface_color, layer_color, layer_opac);
Ci = surface_color;}
Shape Generation
• Disks and Rings– disks and rings can be generated
using distance and either smoothstep (for a disk) or pulse (for a ring).
– this pulse is generated by 1 - smoothstep(radius - fuzz, radius, d)
surface ring(){
color surface_color, layer_color; color layer_opac;float fuzz = 0.025; color blue = color (0,0,1);point center; float radius, half_width; float d;surface_color = Cs; layer_color = blue;center = (0.5, 0.5, 0); /* position of ring */radius = 0.35; /* radius of ring */half_width = 0.05; /* 1/2 width of ring */d = distance(center, (s, t, 0));layer_opac = pulse(radius - half_width, radius + half_width, fuzz, d);surface_color = blend(surface_color, layer_color, layer_opac);Ci = surface_color;
}
surface disk(){
color surface_color, layer_color; color layer_opac;float fuzz = 0.025; color blue = color (0,0,1);point center; float radius; float d;surface_color = Cs; layer_color = blue;center = (0.5, 0.5, 0); /* location of center of disk */radius = 0.35; /* radius of disk */d = distance(center, (s, t, 0));layer_opac = 1 - smoothstep(radius - fuzz, radius, d);surface_color = blend(surface_color, layer_color, layer_opac);Ci = surface_color;
}
Shape Generation
• Lines
surface line(){
color surface_color, layer_color;color layer_opac;float fuzz = 0.025;color green = color (0,0.5,0);point p1, p2;float half_width;float d;
surface_color = Cs;layer_color = green;p1 = (0.25, 0.15, 0); /* endpoint #1 */p2 = (0.85, 0.7, 0); /* endpoint #2 */half_width = 0.05; /* 1/2 line width */d = ptlined(p1, p2, (s, t, 0));layer_opac
= 1 - smoothstep(half_width - fuzz, half_width, d);surface_color
= blend(surface_color, layer_color, layer_opac);Ci = surface_color;
}
surfacemoon(){
color surface_color, layer_color;color layer_opac; float fuzz = 0.01;float circle1, circle2, radius, d; point center;surface_color = color (0.05, 0.05, 0.15);fuzz = 0.01;
/* moon radius */radius = 0.45;
/* moon color */layer_color = color(1, 1, 0.9);
/* first circle */center = (.5, .5, 0); d = distance(center, (s, t, 0));circle1 = 1 - smoothstep(radius - fuzz, radius, d);
/* second circle */center = (.65, .5, 0); d = distance(center, (s, t, 0));circle2 = 1 - smoothstep(radius - fuzz, radius, d);
/* use difference of two circles to create moon */layer_opac = difference(circle1, circle2);surface_color = blend(surface_color, layer_color, layer_opac);Ci = surface_color;
}
Shape Generation• Boolean Operations
– various boolean operations based on disk and square shapes.
disk = D
square = S
union(D,S)
intersection(D,S)
difference(D,S)
difference(S,D)
complement(difference(D,S))
union(difference(S,D), difference(D,S))
surfacediskring(){
color surface_color = 0, layer_color, color layer_opac;float fuzz = 0.01; point center; float ss, tt;float radius, d, half_width; float disk, ring;/* disk */ss = repeat(s, 2); tt = repeat(t, 2);center = (0.5, 0.5, 0); radius = 0.35;d = distance(center, (ss, tt, 0));disk = 1 - smoothstep(radius - fuzz, radius, d);/* ring */ss = repeat(s, 5); tt = repeat(t, 5);center = (0.5, 0.5, 0); radius = 0.35; half_width = 0.05;d = distance(center, (ss, tt, 0));ring = pulse(radius - half_width,
radius + half_width, fuzz, d);/* bool disk & ring */layer_color = color (1, 0.2, 0.2);layer_opac = union(difference(disk, ring),
difference(ring, disk));surface_color
= blend(surface_color, layer_color, layer_opac);Ci = surface_color;
}
