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pocketmoon
05-29-2002, 11:42 PM
Hi oglers

Slighty OT ? I'm trying to get a couple of octaves of perlin-esque noise out of a vertex shader with room to spare for some other calcs.

The smallest 3D noise shader I've seen is the vnoise effect from the Nvidia SDK/Effects browser, which is 127 instructions for 1 octave of 3d noise. This saves instructions by doing a 32 element array lookup and doesnt use an 'easy' function to interpolate between lattice values.

The one I've come up with is 66 instruction and uses a hashing function to determine to lattice noise values (rather than a lookup) and does a nice easy between them for smooth noise.

the basic hash function is:
n = x+y*57.0+z*17.0;
n = (n*(n*n*15731.0+789221.0)+1376312589.0);
n = n / 65535.0;
n = n - floor(n);
n = n * 2.0 - 1.0;

The vertex shader follows so any comments/ideas on making it smaller please! It's a new version that I haven't tested yet so there may be some typos'

!!VP1.0
# Vertex program procedural noise

# Faked Perlin-style 3D Noise
# repeatable random numbers for given vertex position.
# Interpolates *bilinearly* between 4 neighbours to give a smooth result
#
# v1.1
# 66 instructions but I'm sure I can save a few more http://www.opengl.org/discussion_boards/ubb/wink.gif
# Rob James 2002
# pocketmoon@ntlworld.com

#c16 1 2 3 4
#c13 freq amp 3.0 1.0
#c18 1 57 17 0
#c19 15731.0 789221.0 1376312589.0

#scale up the vector

#calc the fractional parts and store in R10
EXP R3.y, R0.x;
MOV R10.x, R3.y;

EXP R10 .y, R0.y;

EXP R3.y, R0.z;
MOV R10.z, R3.y;

#floor (R0)

#calc the slerp parts sx sy sz and stick in R11
MUL R4, R3, R10;
MUL R11, R4, R10;

#now look up eight noise values in R12 and R13
#hash into R3 and R4 initially using
# n = x + 57 * y + 17 * z
# MOV R1, R0;
#MUL R2, R0 , c[18];
#DP3 R3.x, R2, c[18].xxxx;
DP3 R3.x, R0, c[18];

DP3 R3.y, R0, c[18];

DP3 R3.w, R0, c[18];

DP3 R3.z, R0, c[18];

#hmm
DP3 R4.x, R0, c[18];

DP3 R4.w, R0, c[18];

DP3 R4.y, R0, c[18];

DP3 R4.x, R0, c[18];

#now do the mashing!
# n = (n*(n*n*15731)+789221)+1376312589
# n = n /65535
# dont ask how I came by those numbers!

MUL R1, R3, R3;
MUL R3, R1, c[20].xxxx;

MUL R1, R4, R4;
MUL R4, R1, c[20].xxxx;

#keep fractional part
EXP R1.y, R3.x;
MOV R3.x, R1.y;

EXP R1.y, R3.y;
MOV R3.y, R1.y;

EXP R1.y, R3.z;
MOV R3.z, R1.y;

EXP R1.y, R3.w;
MOV R3.w, R1.y;

EXP R1.y, R4.x;
MOV R4.x, R1.y;

EXP R1.y, R4.y;
MOV R4.y, R1.y;

EXP R1.y, R4.z;
MOV R4.z, R1.y;

EXP R1.y, R4.w;
MOV R4.w, R1.y;

#multiply by 2 and subtact 1
#this gives a range -1 to 1

#a = u + t * (v - u)
#NB Proper slerps http://www.opengl.org/discussion_boards/ubb/wink.gif
#This does 4 at once

#two slerps
MOV R4, R3.ywww;

#one final slerp
MOV R3.x, R2.y;

MOV R8.w, c[12].w;
MUL R8.xyz, v[NRML], R3.x;

MAX o[COL0], R3, -R3;

DP4 o[HPOS].x, c[0], R8;
DP4 o[HPOS].y, c[1], R8;
DP4 o[HPOS].z, c[2], R8;
DP4 o[HPOS].w, c[3], R8;

END

Julien Cayzac
05-30-2002, 05:18 AM
Originally posted by pocketmoon:

Slighty OT ? I'm trying to get a couple of octaves of perlin-esque noise out of a vertex shader with room to spare for some other calcs.

I think you're absolutely ON topic, since you discuss about an OpenGL vertex program (which is an advanced topic).

It's funny how things just happen: I was thinking about "enhancing" the vertex shader presented in the lecture available on http://www.jcabs-rumblings.com/GDC2001.html with a noise function, and voila, you just posted it http://www.opengl.org/discussion_boards/ubb/smile.gif

Anyway, your implementation looks quite neat to me.

Julien.

Edit: the UBB "url" thing just sucks.

[This message has been edited by deepmind (edited 05-30-2002).]

pocketmoon
05-30-2002, 05:29 AM
Great minds think alike Julien http://www.opengl.org/discussion_boards/ubb/smile.gif

I'll check out that gdc2001 rumbling.

I'm of course hoping that Nutty will get bored and come up with 8 octave 3D noise in 40 instructions...

I sent it to simon green @ nvidia since he wrote the version in the Effects Browser, but he must be out of office.

Nutty
05-30-2002, 07:28 AM
hehehe.. I think your opinion of my abilities is considerably more than they truly are.

What is it you want exactly? The VP making smaller/less instructions?

Nutty

davepermen
05-30-2002, 08:04 AM
yes, approximated perlin noise with as much octaves as possible in as less instructions as possible. well.. i think you can do it, nutty.. (or should i try? could you write me the basecode and i'll write the noise-func, okay nutty? http://www.opengl.org/discussion_boards/ubb/wink.gif)