Often times render tests of multiple versions of a shader are necessary. Instead of rendering test frames one at a time we can use a TOP network to speed up this process.
IMPORTANT – For Arnold render ROPs to work inside a TOP net in 20.5 add the variable ‘HOUDINI_PATH’ to the parameter Unset Variables in Job Parms on the localscheduler.
Inside a TOP network the wedge node allows us to create work items that alter an attributes in our scene.
On the first wedge node initialize a wedge attribute in this case we want to change the IOR in a shader so we create the attribute ‘P@iortest’ which can be referenced in our shading network. This will create 5 different wedges of our scene where the value of iortest will be stepped starting at 1.5 and ending at 2.8. Chaining wedges will create a nested wedge which allows you to run tests per wedge, in the sample the roughness value will be wedged three ways per IOR wedge.
In the parameter you are wedging reference the attribute by typing P@ then the attribute name. This will change per work item when the TOP net is cooked.
In order to prevent the output render from being over written on each wedge we can reference the current wedge index by adding `P@wedgeindex` to our out put file name. In Houdini in order to evaluate an expression as a string back tics are placed around the expression.
A ropfetch node is used to execute the Arnold rop in our TOP net. Add the path to arnold rop to the ROP Path parameter also change the Frames and Batching to evaluate with ROP configuration.
Set the top output and cook it to generate all the wedge frames at once.
To schedule multiple render tests and wedges to run all at once use a wait for all between tests to reset the wedging process.