How to get JSON formatted strings from Ramps

Forums Technical Discussion How to get JSON formatted strings from Ramps

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zengchen: Member; 77 posts; Joined: Feb. 2017; Offline

Nov. 1, 2020 1:59 a.m.

Hi all:

I tried the H18.5's new VEX function - ramp_unpack / ramp_lookup yesterday.

But I'm confused with the introduction of the ramp_unpack function.

Ramps are commonly packed as JSON formatted strings by Houdini operations.

To my understanding, the ramp_unpack's string parm need a JSON formatted strings from ramp channel.
But how can I get the right json string?

I tried the “Attribute from Parameters” SOP, but the dict(will be converted to JSON use json_dumps function) it gets from ramp channel seems is not the right format which ramp_unpack needs.
I post my hip here.

Does anyone can help me? Thanks.

Edited by zengchen - Nov. 1, 2020 05:51:07

Attachments:
zzzz.png (25.0 KB)
test.hip (86.1 KB)

My Youtube Channel [www.youtube.com]


zengchen: Member; 77 posts; Joined: Feb. 2017; Offline

Nov. 1, 2020 7:13 a.m.

Ok, I finally find the “Flatten Ramps” option on “Attribute from Parameters” SOP

it works correctly this time…

I find it can use dict attribute to store ramp / ~~multiparms~~ now in Houdini 18.5, it is really nice.

PS: the “Attribute from Parameters” SOP always grabs the parameter values at the current time. So it seems impossible to get right multiparms if the parms are changing with time.

Edited by zengchen - Nov. 1, 2020 11:28:59

Attachments:
2020-11-01_201116.png (16.6 KB)
test_fixed.hip (84.1 KB)

My Youtube Channel [www.youtube.com]


OdFotan: Member; 192 posts; Joined: April 2015; Offline

June 4, 2021 9:45 p.m.

Thanks,

I would wanna know if it’s possible to pack it back again, to the string argument,

Or should we have to have it as those 3 arrays if we want to carry it along the node tree as a changeable attribute?


OdFotan: Member; 192 posts; Joined: April 2015; Offline

June 6, 2021 3:22 p.m.

I would need to know that now,

Because the ramp_lookup function doesn't get me the same result when given the three arrays:

I'll log this as a bug to SideFX,
If someone knows a way to fix this, or how to pack the ramp back again, I'd like to know. :-)

hip file attached:

Edited by OdFotan - June 6, 2021 15:29:29

Attachments:
giphy.gif (558.8 KB)
ramp_lookup() bug.hiplc (130.4 KB)
Screenshot 2021-06-06 at 21.10.13.png (12.5 KB)


jlait: Staff; 6169 posts; Joined: July 2005; Offline

June 7, 2021 11:35 a.m.

The ramp_lookup() for arrays is a wrapper around what used to be ramp_lookup in pyro_aaramp. That did a linear warp of the sample position into a uniform key distribution, and then sampled the ramp as if the keys were uniform. I'm guessing maybe the full key spline function wasn't present when that was written, and it "gets away" with it for many ramp types as the key spacing isn't important. But for bsplines it is pretty important!

Fortunately there is a workaround, rather than ramp_lookup() you can go directly to the spline function:

    y = spline(s[]@r_basis, x, f[]@r_val, f[]@r_key);

Hopefully we can fix ramp_lookup, but you probably want to use the spline() version for backwards compatibility in 18.5 for a while.


OdFotan: Member; 192 posts; Joined: April 2015; Offline

June 8, 2021 4:15 p.m.

Interesting. I didn't expect the spline function to work it because the docs didn't mention 'bspline' as an possible option for the basis argument.

Thank you.


jlait: Staff; 6169 posts; Joined: July 2005; Offline

June 10, 2021 9:36 a.m.

Ah, good point, the spline docs have not been updated. It uses the same underlying code as the Ramp, so thus in practice they will remain in sync.

18.5.605 will have ramp_lookup() working as expected, and adds ramp_pack to do the to-string operation if you need it.


papsphilip: Member; 385 posts; Joined: July 2018; Offline

Oct. 13, 2021 12:26 p.m.

How can i write a ramp to a json file? i ma trying to construct a dictionary but i am stuck here

import json

node = kwargs['node']
ramp = node.parm('ramp').multiParmInstances()
num = node.parm('ramp').multiParmInstancesPerItem()

dict = {
    'point': []
}
for p in ramp:
    data = {}
    for i in range(num): 
        if str(i+1) in p.name():
            value = p.eval()
            name = p.name()
            data[name] = value 
    dict['point'].append[data]
 
print(dict)

Edited by papsphilip - Oct. 13, 2021 12:28:36


tamte: Member; 8520 posts; Joined: July 2007; Online

Oct. 13, 2021 12:46 p.m.

papsphilip
How can i write a ramp to a json file? i ma trying to construct a dictionary but i am stuck here

there is an error in this line:

dict['point'].append[data]

should look like this

dict['point'].append(data)

beyond that I'm not sure if you are trying to match specific json structure of ramp parameter, like the one that Attribute From Parameters is using or keeping it as custom, but this should at least fix the error

Edited by tamte - Oct. 13, 2021 12:46:58

Tomas Slancik
FX Supervisor
Method Studios, NY


papsphilip: Member; 385 posts; Joined: July 2018; Offline

Oct. 13, 2021 12:52 p.m.

tamte
beyond that I'm not sure if you are trying to match specific json structure of ramp parameter

i am trying to end up with a json file that looks like this:

ramp name

-point1
--pos
--val
--interp

-point2
--pos
--val
--interp

-point3
--pos
--val
--interp

the error got fixed indeed but the dictionary is messed up

Edited by papsphilip - Oct. 13, 2021 12:53:04


papsphilip: Member; 385 posts; Joined: July 2018; Offline

Oct. 13, 2021 1:16 p.m.

ok i had to turn my loops inside out

import json

node = kwargs['node']
ramp = node.parm('ramp').multiParmInstances()
num = node.parm('ramp').multiParmInstancesPerItem()

dict = {
    'point': []
}

for i in range(num): 
    data={}
    for p in ramp:
        if str(i+1) in p.name():
            value = p.eval()
            name = p.name()
        
            data[name] = value 
            
    dict['point'].append(data)   
    
print(dict)


tamte: Member; 8520 posts; Joined: July 2007; Online

Oct. 13, 2021 1:17 p.m.

papsphilip
i am trying to end up with a json file that looks like this:
...

instead of doing each point as a separate dict value I'd suggest doing a list
here is how it would look like for example:

parm = node.parm('ramp')
ramp = parm.evalAsRamp()
interplookup = [hou.rampBasis.Constant, hou.rampBasis.Linear, hou.rampBasis.CatmullRom, hou.rampBasis.MonotoneCubic, hou.rampBasis.Bezier, hou.rampBasis.BSpline, hou.rampBasis.Hermite]

keylist = []
for i, key in enumerate(ramp.keys()):
    data = { "pos": key,
             "value": ramp.values()[i],
             "interp": interplookup.index(ramp.basis()[i])}    
    keylist.append(data)

dict = { parm.name(): keylist }
print(dict)

but obviously its up to you

Edited by tamte - Oct. 13, 2021 13:28:18

Tomas Slancik
FX Supervisor
Method Studios, NY


papsphilip: Member; 385 posts; Joined: July 2018; Offline

Oct. 13, 2021 1:41 p.m.

tamte
ramp = parm.evalAsRamp()

This is very helpful thank you! also i didn't know about the evalAsRamp().
How can you set the ramp parameters from the dict you just made?

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