I'm afraid the probability values of the Random operator can't be edited on the fly. They're are evaluated only once at the start. However you can do this using a selector operator, two random number generators and an expression to get a result similar to this:
To do this:
- Create a new Selector
node and wire the Light segment to input1, the Mid segment to input2, and the dark segment to input3.
- Export the Selector node's Index
- Attach a new Arithmetic
node to the Index property.
- Create a new Random number node and set the min value to 0.0 and the max to 0.5, wire this to the Arithmetic node's first input.
- Create a second Random number node and set the min value to 0.5 and the max to 1.0, wire this to the Arithmetic node's second input.
- Change the Arithmetic node's mode to Expression and enter the following- if(Input1>XSplinePosition,1,
This is testing the current position on the spline against a randomly generated number. As the position of the spline increases the probability of it selecting the first segment decreases. The same applies for the second If statement except this time it is checking to see if the segment it near the end of the spline.
The final graph should look like this:
I've attached a sample file for you to check out but if you have any further questions please let me know.