/* Renamed to PQslateroofd.sl for RMR -- tal AT renderman DOT org */
/*
slateroofd.sl - a displacement shader to produce tiles on a roof
Parameters:
Km: Maximum displacement of tiles;
sfreq: number of tiles on the s direction
tfreq: number of tiles in the t direction
maxadd: the maximum amount of overlap of one tile and another
ramp: the amount of a tile used for the initial rise to the maximum height
a value between 0 and 1
gap: the size of the gap between one tile and the next in the s direction,
measured as a proportion of the tile (so the value of gap must lie between 0
and 1)
factor: a seed used for adjusting the randomness - if you have two roofs with
the same sfreq, tfreq change the value of factor to ensure they have a
different random patterning. A value > 20 works best
Description
This routine produces a random tiled effect. In the s direction the
tiles are regular, with every other row offset by half a tile width, as
normal roof tiles would be. Each tile is expanded by a random amount in
the t direction so that it overlaps the tile 'below' it. No randomness
is incorporated in the s direction, which remains regular. The routine
first determines the dimensions of the current tile, and then works out
the surface displacement according to a simple formula: a sharp ridge at
the bottom of the tile, gaps to either side and the whole tile gently
sloping towards zero at the top of the tile. It then looks to see if the
point we are considering is actually in the zone of overlap with the
tile 'above' the current one. If it is we replace the displacement we are
considering with one calculated for the tile above, being a little
careful to ensure there are no sudden jumps in displacement.
Peter Quint 17/11/2000
*/
displacement
PQslateroofd( float Km = 1.0,
sfreq = 10,
tfreq = 10,
maxadd = .5,
ramp = .1,
gap = .05,
factor = 22.838)
/* sfreq and tfreq must not be below 3 */
{
uniform float swidth = 1 / sfreq, /* Tile width in the s directio */
twidth = 1 / tfreq, /* ditto for the t direction */
offset = swidth / 2; /* the amount by which alternate rows are offset */
float scoord = s, tcoord = 1 - t; /* re map the t coord so that the coving is at the top */
float stile, ttile, /* An integer identifying the current tile */
s_offset, t_offset, /* Offsets withing the current tile, between 0, 1 */
newstile, newscoord, /* Used in calculations to identify an overlapping tile */
cs, ct; /* Coordinates set to the centre of the tile and fed into the noise function */
float add, /* Add, between 0 and 1, hold the amount the current tile overlaps the next */
news_offset,
disps, dispt, disp, dispo, /* Displacements - s direction, t direction, final displacement, and
displacement for the non-overlapping tile */
temp_s_offset,
temp_t_offset, newadd;
normal Nf = normalize(N);
float spacescale = length(vtransform("shader", Nf));
vector Ndisp = Nf * (1 / max(spacescale,1e-6));
/* Work out which tile we are in, and the offset within that tile */
ttile = tcoord / twidth;
if (mod(ttile,2) >= 1)
scoord = scoord + offset; /* Displace alternate rows */
stile = scoord / swidth;
s_offset = stile - floor(stile);
t_offset = ttile - floor(ttile);
stile = floor(stile);
ttile = floor(ttile);
/* Work out the displacement assuming the point is in the
current tile */
if (ttile < tfreq - 1)
{
/* the noise function is always taken at the same point in the tile
normally the center, except in the short tiles which lie at the
start and end of an offset row, where the middle of the left side
of the tile is used */
ct = ttile + .5;
cs = stile + .5;
if ((mod(ct,2) >= 1) && ((stile == 0) || (stile == sfreq)))
/* An offset row, so we must deal with the half tiles */
cs = stile;
add = noise(cs * factor, ct * factor) * maxadd;
}
else
/* the very bottom row cannot expand */
add = 0;
/* now calculate the displacement */
temp_t_offset = t_offset / (1 + add);
/* the above adjusts t_offset so that it runs from 0 to 1 within the expanded tile */
if (1 - temp_t_offset <= ramp / (1 + add))
dispt = Km / 2 + smoothstep(0, ramp / (1 + add), (1 - temp_t_offset)) * Km / 2;
else
dispt = Km / 2 + smoothstep( 0, 1 - ramp /(1 + add), temp_t_offset) * Km / 2;
if (s_offset > .5)
temp_s_offset = 1 - s_offset;
else
temp_s_offset = s_offset;
if (temp_s_offset < gap * (1 + add))
disps = smoothstep(0, gap * (1 + add), temp_s_offset) * Km;
else
disps = Km;
dispo = min(disps, dispt);
disp = dispo;
/* Work out whether the point is in fact in another tile
storing the new tile in stile, ttile and new offset
in s_offset, t_offset */
if ((t_offset <= maxadd) && (ttile >= 1))
{
/* the point might be in another tile */
if (mod(ttile,2) >= 1)
/* We are in an offset tile row adjust the scoord appropriately for
the row below */
newscoord = scoord - offset;
else
newscoord = scoord + offset;
newstile = newscoord / swidth;
news_offset = newstile - floor(newstile);
newstile = floor(newstile);
/* Now calculate cs, ct the reference point for the noise calculation */
ct = ttile - .5;
cs = newstile + .5;
if ((mod(ct,2) >= 1) && ((newstile == 0) || (newstile == sfreq)))
/* An offset row, so we must deal with the half tiles */
cs = newstile;
newadd = noise(cs * factor, ct * factor) * maxadd;
if (t_offset <= newadd)
/* if t_offset <= newadd we are actually in the overlapping tile */
{
/* set parameters to overlapping tile */
ttile = ttile - 1;
stile = newstile;
t_offset = t_offset + 1;
s_offset = news_offset;
add = newadd;
}
/* calculate the displacement again */
t_offset = t_offset / (1 + add);
if (1 - t_offset <= ramp / (1 + add))
{
dispt = Km / 2 + smoothstep(0, ramp / (1 + add), (1 - t_offset)) * Km / 2;
}
else
dispt = Km / 2 + smoothstep( 0, 1 - ramp, t_offset) * Km / 2;
if (s_offset > .5)
s_offset = 1 - s_offset;
if (s_offset < gap / (1 + add))
disps = Km * smoothstep(0, gap / (1 + add), s_offset);
else
disps = Km;
disp = min(disps, dispt);
disp = max(dispo,disp);
/* taking the maximum of dispo, disp ensures that there
are no discontinuities */
}
P += Nf * (disp / max(spacescale, 1e-6));
/*printf("disp = %f\n",disp);*/
N = calculatenormal(P);
}