"position cam" AOV

[Riccardo Cecchinato]

Hello dear Gaffer devs!

I am trying to setup a custom AOV for compositing, that allows them to sample the position of each object of the scene relative to the render camera.

In maya I would use the samplerinfo node using the "camera position" outputs, but in Gaffer 1.5.2 I am not able to find an equivalent node.

I played around with the Arnold "Utility" node in connection with "SpaceTransform", trying to convert the p info from world to camera, but I cannot get the correct result. Probably I am not using the SpaceTransform node in the correct way.

Do you have any suggestions/ideas?

Thank you in advance for your help,

Riccardo

 

[Sachin Shrestha]

Hi Riccardo,

You will probably need to set the input type in the SpaceTransform node to vector for tit work correctly. Attached is a snapshot with the regular world P from utility on the left and the camera P on the right. SpaceTransform settings are on the bottom right node editor.

Hope this helps.

-Sachin

[Riccardo Cecchinato]

Hello Sachin,

thanks a lot for your help!

I already got that result but - as far as I can tell - it is not the correct behaviour.

Normally the "position to cam" AOV should look something like this (confirmed by compositing):

The shading node being:

Does it ring any bells?

Thank you again.

Riccardo

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	Riccardo Cecchinato
	Lead Lighting
	stimstudio.com

[Paolo DE LUCIA]

Position to screen in the spaceTransform :

import Gaffer
import GafferArnold
import GafferScene
import IECore
import imath

Gaffer.Metadata.registerValue( parent, "serialiser:milestoneVersion", 1, persistent=False )
Gaffer.Metadata.registerValue( parent, "serialiser:majorVersion", 4, persistent=False )
Gaffer.Metadata.registerValue( parent, "serialiser:minorVersion", 11, persistent=False )
Gaffer.Metadata.registerValue( parent, "serialiser:patchVersion", 0, persistent=False )

__children = {}

__children["StateVector"] = GafferArnold.ArnoldShader( "StateVector" )
parent.addChild( __children["StateVector"] )
__children["StateVector"].loadShader( "state_vector" )
__children["StateVector"].addChild( Gaffer.V2fPlug( "__uiPosition", defaultValue = imath.V2f( 0, 0 ), flags = Gaffer.Plug.Flags.Default | Gaffer.Plug.Flags.Dynamic, ) )
__children["SpaceTransform"] = GafferArnold.ArnoldShader( "SpaceTransform" )
parent.addChild( __children["SpaceTransform"] )
__children["SpaceTransform"].loadShader( "space_transform" )
__children["SpaceTransform"].addChild( Gaffer.V2fPlug( "__uiPosition", defaultValue = imath.V2f( 0, 0 ), flags = Gaffer.Plug.Flags.Default | Gaffer.Plug.Flags.Dynamic, ) )
__children["ShaderAssignment4"] = GafferScene.ShaderAssignment( "ShaderAssignment4" )
parent.addChild( __children["ShaderAssignment4"] )
__children["ShaderAssignment4"].addChild( Gaffer.V2fPlug( "__uiPosition", defaultValue = imath.V2f( 0, 0 ), flags = Gaffer.Plug.Flags.Default | Gaffer.Plug.Flags.Dynamic, ) )
__children["PathFilter59"] = GafferScene.PathFilter( "PathFilter59" )
parent.addChild( __children["PathFilter59"] )
__children["PathFilter59"].addChild( Gaffer.V2fPlug( "__uiPosition", defaultValue = imath.V2f( 0, 0 ), flags = Gaffer.Plug.Flags.Default | Gaffer.Plug.Flags.Dynamic, ) )
__children["Flat"] = GafferArnold.ArnoldShader( "Flat" )
parent.addChild( __children["Flat"] )
__children["Flat"].loadShader( "flat" )
__children["Flat"].addChild( Gaffer.V2fPlug( "__uiPosition", defaultValue = imath.V2f( 0, 0 ), flags = Gaffer.Plug.Flags.Default | Gaffer.Plug.Flags.Dynamic, ) )
__children["StateVector"]["parameters"]["variable"].setValue( 'P' )
__children["StateVector"]["__uiPosition"].setValue( imath.V2f( -346.135742, -420.145081 ) )
__children["SpaceTransform"]["parameters"]["input"].setInput( __children["StateVector"]["out"] )
__children["SpaceTransform"]["parameters"]["type"].setValue( 'vector' )
__children["SpaceTransform"]["parameters"]["to"].setValue( 'screen' )
Gaffer.Metadata.registerValue( __children["SpaceTransform"]["out"], 'compoundNumericNodule:childrenVisible', True )
__children["SpaceTransform"]["__uiPosition"].setValue( imath.V2f( -333.866455, -421.945068 ) )
__children["ShaderAssignment4"]["filter"].setInput( __children["PathFilter59"]["out"] )
__children["ShaderAssignment4"]["shader"].setInput( __children["Flat"]["out"] )
__children["ShaderAssignment4"]["__uiPosition"].setValue( imath.V2f( -310.226074, -421.945068 ) )
__children["PathFilter59"]["paths"].setValue( IECore.StringVectorData( [ '.../...' ] ) )
__children["PathFilter59"]["__uiPosition"].setValue( imath.V2f( -294.41745, -417.26236 ) )
__children["Flat"]["parameters"]["color"]["b"].setValue( 0.0 )
Gaffer.Metadata.registerValue( __children["Flat"]["parameters"]["color"], 'compoundNumericNodule:childrenVisible', True )
__children["Flat"]["parameters"]["color"]["r"].setInput( __children["SpaceTransform"]["out"]["x"] )
__children["Flat"]["parameters"]["color"]["g"].setInput( __children["SpaceTransform"]["out"]["y"] )
__children["Flat"]["__uiPosition"].setValue( imath.V2f( -323.866699, -421.945068 ) )


del __children

[Paolo DE LUCIA]

Althought I don't see the point of this pass that can be generated in comp with a simple expression, multiplied by the alpha.

r = (x/(width/2)-1)
g = (y/(height/2)-1)

[Sachin Shrestha]

Aah yes, I think the utility shader's P is relative to the bbox so your state vector node is the correct answer. Or the oslInPoint node would do as well.

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[Riccardo Cecchinato]

Hello Paolo,

thanks a lot, your node tree gives a result much closer to what I seek, thank you!

I understand your second point about generating the pass in comp, but I tested both methods and compared them, and I can clearly see a difference between the two, both visually and in values (render on the left, nuke on the right, same render pass):

 

Not sure why this difference happens. Do you have any idea about this different behaviour? 

I must admit I do not know much about the topic, it is a compositing request I need to deliver them asap, I had no time to do much research (even if I understand the theoretical usage for it).

Sachin,

thanks again and I'll test the oslInPoint too!

Riccardo

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[Paolo DE LUCIA]

Ah my bad,
Because it's world space units converted to screen space, a unit looks bigger closer to the camera than far away... the variation of value results from the perspective.
Thus the 2d trick is not an option.

[Vinicius Villela]

I don't know if this helps, but this is how I configure position pass.

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Att. Vinicius Villela
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