Heavy Smoke Shader

[kevin]

hi, all. I am trying to underdtand what's going on the shader network of heavy smoke in FXtools from SESI.I understand the red parts which generates the random points based on the id. what I am not sure is the blue part. what I guessed is that the local shading point of metaball is inverse transformed to the origin to stick the noise pattern to the metaball. but can anyone explain to me what is going on the blue parts to get better understand,please? I also can't get why those red and blue parts are added together before feeding into the pos of turbnoise1. Any help would be appreciated. Thanks.

Edited January 4, 2008 by kevin

[Jason]

hi, all. I am trying to underdtand what's going on the shader network of heavy smoke in FXtools from SESI.I understand the red parts which generates the random points based on the id. what I am not sure is the blue part. what I guessed is that the local shading point of metaball is inverse transformed to the origin to stick the noise pattern to the metaball. but can anyone explain to me what is going on the blue parts to get better understand,please? I also can't get why those red and blue parts are added together before feeding into the pos of turbnoise1. Any help would be appreciated. Thanks.

The red bit at the top is just generating a random offset in position based on the each unique metaball (using the "id" integer attribute as a unique key) which is a constant offset per metaball due to id being unique and constant for each metaball. The blue bit is a varying position based on the rest space of the metaball. So if you add them together, each metaball has a nice uniquely offset position from which the turbulent noise is looked up. This results in a unique noise pattern per metaball.

I do think that the network could be segmented into network boxes and documented a little more clearly, but that's the gist of it.

I hope this helps,

Jason.

[kevin]

The red bit at the top is just generating a random offset in position based on the each unique metaball (using the "id" integer attribute as a unique key) which is a constant offset per metaball due to id being unique and constant for each metaball. The blue bit is a varying position based on the rest space of the metaball. So if you add them together, each metaball has a nice uniquely offset position from which the turbulent noise is looked up. This results in a unique noise pattern per metaball.

I do think that the network could be segmented into network boxes and documented a little more clearly, but that's the gist of it.

I hope this helps,

Jason.

Hi, Jason. Thanks for the quick reply. It is much clear now. I was taking a shower and thinking about the 3d Space, then got an idea like you explained to me . I also did not understand red part(new attached image) whcih uses the dPdz(Floating point step size for volume rendering.) why the noise density is multiplied by -1 and dPdz, and then it uses logarithmic exponentiation function and finally, it is subtracted by -1? I am totally lost this part.

Thanks in advance.

Edited January 4, 2008 by kevin

[kevin]

Hi, Jason. Thanks for the quick reply. It is much clear now. I was taking a shower and thinking about the 3d Space, then got an idea like you explained to me . I also did not understand red part(new attached image) whcih uses the dPdz(Floating point step size for volume rendering.) why the noise density is multiplied by -1 and dPdz, and then it uses logarithmic exponentiation function and finally, it is subtracted by -1? I am totally lost this part.

Thanks in advance.

I got it!! a simple exponential fading with distance(step size).....

Thanks.