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Working With Switches 

 Blog Entry #5, January 26th, 2020

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Intro

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Switches are probably one of the most useful tools in Houdini. They can allow you to switch(just as it's name describes) between different geometry, simulation outputs and inputs, and more. 

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However, telling a switch when to switch, or telling it when to do it's job might be a bit difficult. More so if you are either new to VEX, Hscript, or Houdini in general. This article is going to be a reference, or go to sheet for switch commands. Enjoy!

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Switch Commands

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  • Current frame,and floating point frame number: $F, $FF.

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  • Current time: $T or @Time

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  • Switch input number every 50th frame going between 0 and 1: $F%100<50

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  • Use the first input for the first four frames, and the second input afterward: $F >= 5

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  • Switch to the first input at frame 1: $F - 1

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  • The switch will use the second input if there are no errors, if there is, it will switch to the first input: if (strmatch("*Error:*", run("opinfo " + opfullpath("../" + opinput(".", 1)))), 0, 1)

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  • To get the switch node affect certain attributes use: point(), prim(), vertex() or detail() expressions.

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  • Switch to input 0 if there is no other objects in the merge node. If there is, switch to input 1: if(npoints(“../object_merge1/”) != 0, 1, 0)

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  • Delay a simulation by a frame, and pass the previous frame's input data forward: if($F==1, 0, 1)

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  • Make things exactly equal to something in a switch: ==

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  • Make something greater and equal than something: >=

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  • Make something less than and equal than something else: <=

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  • Switch if something is not equal to another value: !=

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References

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