question 1:
in order to understand what is happening here you have to first understand the fundamentals of how POPs works. On each time step acceleration gets interpreted as velocity and then on the following timestep velocity get interpreted as position:
a->v->p
in order to see this in action create a popnet with the oversampling set to 1.
create a location pop that creates 1 point on the first frame.
add a force pop with the a value of 0 10 0
open up the spread sheet and take a look at what happens:
frame 1 : acceleration, no velocity, no change in position.
frame 2 : acceleration, change in velocity, no change in position.
frame 3: acceleration, change in velocity, change in positon.
the point doesn't move until frame 3!
so now lets go back to your original question. Why is the force pop
not working with the velocity pop. this is probably because the values
in the velocity pop are overriding the velocities from the force pop.
so for example in the velocity pop if you set the value to (10,0,0)
the velocity coming out of that pop is always going to be (10,0,0).
but if you do something like ($VX+10,$VY,$VZ) then a velocity of ten
will be added on each time step and you'll be able to see the effect(note this
will be cumulative).
questions 2 and 3 - don't have to much experience doing this the first
things that come to mind are the “slide” and “stick” features of the collision
pop. You might be able to use the state sop to flag a particle as stuck or sliding as soon as it born. might want to look at the creep pop as well.
hope that helps
Luca
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Technical Discussion » some questions about POPs
- lucap
- 31 posts
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Technical Discussion » dealing with nan values
- lucap
- 31 posts
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I posted a similar post on odforce, so I apologize if you are reading this twice.
I have a vex operator that's reading an i3d file, some of the values being returned are nan
values. I was wondering if there's a way to test for nan values and replace them
with something different
eg
if foo==nan then
foo=0
thanks
Luca
I have a vex operator that's reading an i3d file, some of the values being returned are nan
values. I was wondering if there's a way to test for nan values and replace them
with something different
eg
if foo==nan then
foo=0
thanks
Luca
Technical Discussion » hdk group centroid position
- lucap
- 31 posts
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I don't know if there's a function that does this for you (might want to look at UT_BoundingBox). I did it the old fashion way:
FOR_ALL_GPOINTS(gdp, ppt)
{
UT_Vector4 pos4=ppt->getPos();
txSum+=pos4.x()/pos4.w();
tySum+=pos4.y()/pos4.w();
tzSum+=pos4.z()/pos4.w();
}
myCEX=txSum/myTotalPoints;
myCEY=tySum/myTotalPoints;
myCEZ=tzSum/myTotalPoints;
hope that helps
Luca
FOR_ALL_GPOINTS(gdp, ppt)
{
UT_Vector4 pos4=ppt->getPos();
txSum+=pos4.x()/pos4.w();
tySum+=pos4.y()/pos4.w();
tzSum+=pos4.z()/pos4.w();
}
myCEX=txSum/myTotalPoints;
myCEY=tySum/myTotalPoints;
myCEZ=tzSum/myTotalPoints;
hope that helps
Luca
Technical Discussion » HDK: setting NPT and PT in a filter sop
- lucap
- 31 posts
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Technical Discussion » Why exportCHOP .. Needs Export Flat On?
- lucap
- 31 posts
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Not really a direct answer to your question but I thought it might help:
I try too avoid using the export chop and use the chop() expression instead. I've seen people have issues with the export flag/chop that are usually resolved by using the chop expression.
L
I try too avoid using the export chop and use the chop() expression instead. I've seen people have issues with the export flag/chop that are usually resolved by using the chop expression.
L
Technical Discussion » HDK: setting NPT and PT in a filter sop
- lucap
- 31 posts
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Hi,
I'm just getting started in the hdk so don't laugh.
I'm trying to create the local variables NPT and PT in
my sop. looking at the SOP_star example in the toolkit
I get the general gist of how to create and assign value
to NPT and PT.
but, I'm having some trouble figuring out how to calculate
the values that I need to assign to PT and NPT. In the Star sop
these values are derived from the parameters, but my sop
needs to get this information from the incoming sop.
Anybody have ideas on the best way to approach this?
I'd also be curious to know if there's are preexisting functions for
calculating (BBX,BBY,BBZ) , (XMIN,YMIN,ZMIN) OR (XMAX,YMAX,ZMAX)
many thanks
Luca
I'm just getting started in the hdk so don't laugh.
I'm trying to create the local variables NPT and PT in
my sop. looking at the SOP_star example in the toolkit
I get the general gist of how to create and assign value
to NPT and PT.
but, I'm having some trouble figuring out how to calculate
the values that I need to assign to PT and NPT. In the Star sop
these values are derived from the parameters, but my sop
needs to get this information from the incoming sop.
Anybody have ideas on the best way to approach this?
I'd also be curious to know if there's are preexisting functions for
calculating (BBX,BBY,BBZ) , (XMIN,YMIN,ZMIN) OR (XMAX,YMAX,ZMAX)
many thanks
Luca
Technical Discussion » reading image data into a point SOP
- lucap
- 31 posts
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you might also try making a custom sop with vops.
the vop you'll be interested in is the color map vop. Vops will be much
faster than using the point sop.
Luca
the vop you'll be interested in is the color map vop. Vops will be much
faster than using the point sop.
Luca
Houdini Lounge » RFE: Image browser for any Image type file requestor
- lucap
- 31 posts
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Technical Discussion » COOL FOG SHADER
- lucap
- 31 posts
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Go to the forum on odforce.net and do a search for “i3d” and or “fog”.
there have been a few i3d/fog shaders posted. In addition, check out the odwiki and
I believe jason wrote something in tutorial section on i3d as well
All the best
Luca
there have been a few i3d/fog shaders posted. In addition, check out the odwiki and
I believe jason wrote something in tutorial section on i3d as well
All the best
Luca
Technical Discussion » Can't attach files?
- lucap
- 31 posts
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Technical Discussion » VOPs Flocking
- lucap
- 31 posts
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(by the way, is there a way to visualize numeric outputs from VOPs?)
Hi Squid
what I usually do is use a print vop (make sure you have “print to console” turned on in the vop)
What this will do is print the values from your shader into the shell that you started
from. I use this to debug my vex ops all the time. If you're working on windows you will
need to start houdini from a shell(a unix emulator like cygwin is nice) in order to see the values.
Technical Discussion » baking/freezing a displacement to polys
- lucap
- 31 posts
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because you can't get at the code from “generic displace” have a lookat the
code in “Vex Displace Map” you should be able to access this via the type properties.
and as Mario says use colormap() instead of texture
thanks for pointing that out Simon, I just had a look in 8.0.233 and it looks like it's fixed.
all the best
Luca
code in “Vex Displace Map” you should be able to access this via the type properties.
and as Mario says use colormap() instead of texture
SESI If you click on colormap in the vex quick reference html file the link is broken by the way.
thanks for pointing that out Simon, I just had a look in 8.0.233 and it looks like it's fixed.
all the best
Luca
Technical Discussion » bump map and displace map interfering
- lucap
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don't know off the top of my head, any chance you could post a simple .hip
somewhere so I can have a look at it?
somewhere so I can have a look at it?
Technical Discussion » baking/freezing a displacement to polys
- lucap
- 31 posts
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yep, just take the code from your displacement shader and put it into
a vex SOP, refer to the same texture map and you're set.
PS - your code may need a bit of tweaking, in the shading context the
global variables are in “world” space(ie the camera is the origin),
SOPs is in object space.
reply if you run into trouble.
Luca
a vex SOP, refer to the same texture map and you're set.
PS - your code may need a bit of tweaking, in the shading context the
global variables are in “world” space(ie the camera is the origin),
SOPs is in object space.
reply if you run into trouble.
Luca
Technical Discussion » fluid effect...VOPs
- lucap
- 31 posts
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but I was wondering what the benefit would be if I used point clouds….to be honest I am not quite sure what they are other that you can access attributes from them
The benefit of using point clouds(and by point clouds I am referring to the vop functions that at start with “point cloud” or the vex functions that start with “pc”) is that you can refer to geometry, by proximity, at render time.
have a look at the files from the point cloud presentation:
http://www.sidefx.com/exchange/info.php?fileid=208&versionid=208 [sidefx.com]
that should give you some idea.
to be honest I am not quite sure what they are other that you can access attributes from them…..but I thought you could do that with particles too.
You can do it(in sops not shaders) with particles but it would be very slow because you'd have to test against every point. If you wanted to do it with a shader you'd have to used point clouds.
Luca
Technical Discussion » hip files from Point Cloud presentation are up on exchange
- lucap
- 31 posts
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A bunch of example hip files from the Toronto Techincal Evening on point clouds
(May 11th 2005) have now been posted to the exchange.
http://www.sidefx.com/exchange/ [sidefx.com]
(May 11th 2005) have now been posted to the exchange.
http://www.sidefx.com/exchange/ [sidefx.com]
Technical Discussion » dust particles...
- lucap
- 31 posts
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Have a look on odforce
http://www.odforce.net/codex/index.php?page=5&sec=shaders&catlimit=&sorty=&limit=5 [odforce.net]
Peter Bowmar created an atmosphere shader called “Projected Fog”
Assign the shader to an atmosphere object and then parent it
to the light.
http://www.odforce.net/codex/index.php?page=5&sec=shaders&catlimit=&sorty=&limit=5 [odforce.net]
Peter Bowmar created an atmosphere shader called “Projected Fog”
Assign the shader to an atmosphere object and then parent it
to the light.
Technical Discussion » fluid effect...VOPs
- lucap
- 31 posts
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is there a way to directly convert the displacement shader to a VEX sop…..because my first attempt was actually using a vex sop…..and I found it easier to displace normals with a diplacement VOP…
Sure, just copy your vop nework from your displacement shader
and into a VOP geometry operator. reconnect the inputs and outputs
as needed and you should be fine.
Note: you may have to compensate for space changes.
Sops work in “object space” displacement shaders work in “world
space” ie the orgin is the camera. Changing between these
spaces is straight forward, use the spacechange VOP for position
and directionspacechange VOP for direction vectors.
Also to add to the realness of water…
I have been using the waves VOP and would like to figure out how to get the ripples VOP to work the same way….it doesn't work just by converting a float to vector and using an add VOP….
add the “amount” output from the waves and the ripples vops
and use the sum as the input to the displace along normal vop.
Technical Discussion » fluid effect...VOPs
- lucap
- 31 posts
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I have a vex diplacement shader I wrote that is somewhat like water….So there is a grid(the water), and I want to have some sort of geometry birth out of the water,
the first thing that I would do is turn you vex diplacement shader into
a vex Sop. You can used the Sop displaced geometry to birth your particles from, in addition it could also act as a collision surface.
when you render you'd still use your displacement shader on the flat gird.
and have a couple areas where they are separating, to drop back into the water and cause some ripples. Then at the end, the geometry would be above the water, and be separate and still have the same shader.
Not entirly sure what you're asking for… so I'll make a guess:
you want the particles to interact with the water surface when the collide with it.
I'd try using your particles as a point cloud, and have that point cloud
affect your shader.
the following links will give you some information on point clouds and
there usage.
http://odforce.net/wiki/index.php/VexPointCloud [odforce.net]
http://odforce.net/forum/index.php?showtopic=2135 [odforce.net]
all the best
Luca
Technical Discussion » Displaements with ambient occlusion
- lucap
- 31 posts
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try adding the line to the camera's pre-include field. You
can find it under the camera's render tab.
can find it under the camera's render tab.
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