Hello Metacloud

[Guest Swann]

Hello everybody

I'm trying to recreate standard Houdini MetaCloud shader in VOPS and I got some questions. These are only my thoughts about what to do.

* Produced by:

* Side Effects Software Inc

* 123 Fronst Street West, Suite 1401

* Toronto, Ontario

* Canada M5J 2M2

* 416-504-9876

*

* NAME: fluffy.vfl ( VEX )

*

* COMMENTS: Generate a fluffy cloud using metaball geometry

*/

#pragma opname v_metacloud

#pragma oplabel "VEX Meta Cloud"

#pragma label freq "Noise Frequency"

#pragma label offset "Noise Offset"

#pragma label time "Cloud Time"

#pragma label amp "Noise Amplitude"

#pragma label rough "Noise Roughness"

#pragma label turb "Turbulence"

#pragma label limit "Density threshold"

#pragma label perpoint "Per-point noise"

#pragma label summing "Density"

#pragma hint perpoint toggle

#pragma range turb 0 8

#pragma choice summing "sum" "Sum metaball densities"

#pragma choice summing "max" "Choose maximum density"

#pragma range turb 0 10

Content of this part is pretty clear for me

//

// Compute noise on a per metaball basis. We take either the max or the sum of

// the densities.

//

vector

compNoise(vector p; vector freq, off, amp; float rough, now; int turb)

{

int i;

vector scale;

vector nval;

vector4 pp;

pp = p * freq + off;

pp.w = now;

nval = 0;

scale = amp;

for (i = turb; i-- > 0; pp *= 2, scale *= rough)

nval += scale * (vector(noise(pp)) - (.5,.5,.5));

return nval;

}

In the gNoise.h there are couple similar noise functions, althrough not identical so I supose it will be best to go here with InlineVOP. But using oportunity that OldSchool started in his BLOG series of lessons on "Create Custom VOP" I thinking about recreating this function clearly in VOPs without InlineVOP.

Question 1:

1. pp.w //does this mean "dot produkt per-point and w " ?

2. pp *=2 or nval += //what mean sign * and + before # equal ?

image3d

metacloud( vector freq=3; // Noise frequency

vector offset=0; // Noise offset

float time=0; // Time offset

vector amp=.3; // Noise amplitude

float rough=.6; // Noise roughness

int turb=4; // Turbulence

float limit=1; // Maximum density

int perpoint=0; // Do per-point noise calc

string summing="sum"; // Do summing by default

)

no questions here yet

{

vector nval;

vector pp;

float tmp;

density = 0;

if (perpoint)

{

forpoints(P)

{

// Convert to the space of the metaball. Now, P is somewhere in

// the unit sphere.

pp = mspace(P);

1.

- starting from globalVariablesVOP

- density plug to compareVop

- to InlineVOP we pluging Globals "P" and output of compareVOP

- output of InlineVOP will give "nval"

2.

- nval, P, and compareVOP we are pluging to If-Then-BlockVOP

3. inside If-Then-BlockVOP:

- P and nval plugged into pointLoopVOP

4. inside pointLoopVOP

- "pp" it's P after transform to metaball space with a help of metaBallSpaceVOP

// Now, if there's a rest attribute, add it onto the original

// position. This gives us a per-metaball noise offset.

if (isbound("rest"))

pp += mattrib("rest", P);

- propably we can supply "rest" attribute with parameterVOP and add it to P (Question 2: There is written original P, so does this mean big P not the "pp" after transform ?) but we cando the same with a help metaBallAttributeVOP whitch by deflaut is looking for "rest" attribute

Question 3: What means pp+ ? Is it mean the same what normal "pp" and plus means that something is added (rest attribute) to it ?

Question 4: beside, like below with "P+nval", maybe "pp+" should be done by adding output of metaBallAttributeVOP and metaSpaceVOP

nval = compNoise(pp, freq, offset, amp, rough, time, turb);

tmp = mdensity(P + nval);

- we got "nval" but "tmp" hm... with this I got problem, because:

Question 5: There is written "P+nval" and metaDensityVOP is not taking nval in his calculations, so what should I do ? instead metaDensityVOP make addition of big "P" and "nval" ?

if (summing == "sum")

{

density += tmp;

if (density > limit)

break;

}

else if (tmp > density)

{

density = tmp;

if (density > limit)

break;

}

}

}

else

{

// Just compute noise in world space

nval = compNoise(P, freq, offset, amp, rough, time, turb);

density = mdensity(P + nval);

}

density = clamp(density, 0, limit);

}

- we leave this part for now, I don't have idea how to remade most of this, proplably next if-Then-BlockVOP but I completly don't know how to bite "density > limit", "break" and others here.

Question 6: beside, why in the end we are calculating noise in worldSpace ( when condition is not meet) when we need it calculated in metaSpace ?

Thanks

Edited May 11, 2008 by SWANN

[aracid]

Hey

I'll try give it a shot,

Q:

1. pp.w //does this mean "dot produkt per-point and w " ?

A: normally when u define a vector 3 you have 3 floats paired to the variable, vector.x vector.y vector.z

in the case of a vector4 u have an aditional float called w, which i think stands for weight, but u can store any float with.

so theres nothing special involved except with a float u store 1 value, a vector - 3 val, vector4 - 4 val.

Q:

2. pp *=2 or nval += //what mean sign * and + before # equal ?

A:

pp*= 2 actually expands to pp = pp * 2.

or in the case of pp+= 2 expands to pp = pp + 2;

so its just a more efficient method of coding.

Q:

why in the end we are calculating noise in worldSpace ( when condition is not meet) when we need it calculated in metaSpace ?

A:

thats purely because they haven't included a method to introduce the local translations of each metaball.

I think for no reason expect as an example of a simple shader that doesn't include much.

Take a look at the heavy smoke in the FX shelf, included with that is a shader that uses the local space of the metacloud as a coordinate system.

hope any of this was helpful.

[Guest Swann]

Hey

I'll try give it a shot,

Q:

1. pp.w //does this mean "dot produkt per-point and w " ?

A: normally when u define a vector 3 you have 3 floats paired to the variable, vector.x vector.y vector.z

in the case of a vector4 u have an aditional float called w, which i think stands for weight, but u can store any float with.

so theres nothing special involved except with a float u store 1 value, a vector - 3 val, vector4 - 4 val.

Q:

2. pp *=2 or nval += //what mean sign * and + before # equal ?

A:

pp*= 2 actually expands to pp = pp * 2.

or in the case of pp+= 2 expands to pp = pp + 2;

so its just a more efficient method of coding.

Q:

why in the end we are calculating noise in worldSpace ( when condition is not meet) when we need it calculated in metaSpace ?

A:

thats purely because they haven't included a method to introduce the local translations of each metaball.

I think for no reason expect as an example of a simple shader that doesn't include much.

Thanks, it clears some fog from my eyes

Take a look at the heavy smoke in the FX shelf, included with that is a shader that uses the local space of the metacloud as a coordinate system.

hope any of this was helpful.

Yeah, thanks again, I see how break and clamp should be done

Edited May 11, 2008 by SWANN

[Guest Swann]

I forgot that this shader calculates two types of smoke, per-point and normal and this is the reason why it calculates in the end smoke in worldSpace, just to make swimming effect for the smoke-cloud type.

Edited May 12, 2008 by SWANN