Implement PingPong style in Animate2D

[Moros1138]

I took a stab at implementing PingPong, this is the way that seems to make sense to me, might be able to be expressed better.

        case Style::PingPong:
        {
            // calculate time period with time frames of 2 complete sequences
            float pingPongTime =
                fmod(fTime * m_fFrameRate, m_vFrames.size() * 2);

            // calculate the current frame index
            size_t index = (size_t(pingPongTime) % m_vFrames.size());

            // if we're on the second sequence, run in reverse
            if(pingPongTime > m_vFrames.size())
                return (m_vFrames.size() - 1) - index;

            // if we made it here, we're handing the first sequence, run forward
            return index;
        }
        break;

olcPixelGameEngine/utilities/olcUTIL_Animate2D.h

Line 143 in 147c25a

case Style::PingPong:

[Moros1138]

Not even 5 minutes later this occurred to me... no conditionals in our code

        case Style::PingPong:
        {
            float pingPongTime =
                std::abs(std::fmod(fTime * m_fFrameRate, m_vFrames.size() * 2) -
                         m_vFrames.size());

            return (size_t(pingPongTime) % m_vFrames.size());
        }
        break;