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 radians) 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 */ surface rotcross() { 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 staggered by using repeat, whichtile, and odd and/or even to determine if 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 */ surface shiftedblocks() { 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 shaped 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 */ surface rect() { 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; }

surface moon() { 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))

surface diskring() { 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; }

Homework Shader flag.rib, flag.sl, flag.tif