Interval: LerpFunctionInterval() returns toData when played backwards and duration is 0.0

[kamgha]

Description

In order to create a quick workaround solution for #1616, a LerpFunctionInterval() can be used with a duration of 0.0. The idea is, when the Interval gets triggered and returns fromData, it has been played backwards or the cursor of the interval has been set before the position of the interval building block.

At the moment, when the duration is 0.0, the interval returns the toData when played back in both directions (playRate >0 and <0). The expected behaviour is that it returns toData when it gets played back forwards, and fromData when it gets played back backwards, to reset the data range.

The expected behaviour works when the duration is set >0.0, e. g. 0.000000000000001.

Steps to Reproduce

Reproducer:

from panda3d.core import *

from direct.showbase.ShowBase import ShowBase

from direct.interval.FunctionInterval import *
from direct.interval.MetaInterval import *
from direct.interval.LerpInterval import *


class Test(ShowBase):

    def __init__(self):
        ShowBase.__init__(self)

        self.accept('1', self.one)
        self.accept('2', self.two)
        
    def one(self):
        print('pressed 1')
    
        w1 = Wait(2.0)
        w2 = Wait(2.0)
    
        fi = LerpFunctionInterval(self.fi_func, 0.0000000000000000000000000000, 0.0, 1.0)
        #fi = Func(self.fi_func)  # this will/should only trigger in forward direction
        
        self.seq = Sequence(w1, fi, w2)
        self.seq.start()
        
    def fi_func(self, a):
        print('fi_func triggered')
        if a == 1.0:
            print('should only print on forward')
            
        if a == 0.0:
            print('should only print on backward')
            
        print(f'a is {a}')
        print(self.seq.getT())
        
    def two(self):
        print('pressed 2')
        self.seq.setPlayRate(-1.0)
        self.seq.resume()


player = Test()
player.run()

Environment

• Operating system: Windows 8.1
• System architecture: x86_64
• Panda3D version: master, current revision
• Installation method: built from source
• Python version (if using Python): 3.8.18
• Compiler (if using C++): MSVC 14.0 (VS 2015)