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Hello,

I have a ripple sim created with a sphere moving through a grid and the points deforming based on the velocity transferred to said grid.

What I am trying to do is isolate the geometry based on where there are ripples via colour then as the rippled geo begins to settle back into what it was originally have that colour fade back to black.

I'm halfway there I think.  I was able to isolate the rippling parts of my grid by using a facet to compute its normals and then a point SOP to add colour based on the normal in it's Y (@N.y < 1).

I was thinking of trying to use a vop or another point sop to make it so when the normal is between x and y multiply the color by 0.95 to get it to fade over time but was wondering what other ways I could try to do this.

Cheers,

JP

ripple_example_1.hipnc

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vector up = {0,1,0};
float min = ch("Min");
float max = ch("Max");
float dot = dot(up,@N);
float threshold = fit(dot,min,max,0,1);
@Cd *= threshold;

You had the right idea and this is what the dot product does

ripple_example_2.hipnc

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That's almost exactly what I'm looking for, thank you so much!

My knowledge of wrangles isn't so great so what I'm assuming is that:

you're defining the up vector and the min and the max values for the channels you created

then you're getting the dot product from the up vector and the normal

then you're defining the threshold by fitting all the attributes between 0 and 1

then you're multiplying the colour by said threshold so any point being disturbed begins with a colour value of 0 which fades to 1 overtime.

I think that's correct?  Regardless I think this will work with what I need to do and I'm assuming I can rebuild what you've done in a VOP in order to have more control?

Thanks again!

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yup thats it except im not fitting all the attributes, only the dot of the N and up  to 0-1 so it will make a visible difference when we multiply color by it. Because it is returning a narrow range (.995 to 1) as there is not a big difference between the vectors. It also does not fade by time, it is only by the dot - which in this case is basically the difference between N and up, so the further it points away from 0,1,0 the more it is scaled down. You can make this in a VOP pretty easy yea.

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I tried recreating your method in a VOP and have something almost identical (I think).

There is still a difference in the amount of colour your way picks up compared to mine.

I defined my up vector before the vop using the old point sop node and didn't create the min and max values because I assumed they were for your fit in your wrangle example so I just promoted the source min and max in my vop

after I fit the dot product.

Then I multiplied the colour by the dot product and hooked it back into the output color.

Screenshot from my VOP

ripple_example_4.hipnc

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you were dotting with @P.y instead of the up vector u created

ripple_example_5.hipnc

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shoot...

I saw that it was a vector attribute and got confused.

Thank you again for all the help, I really learned a lot from this!

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