How do I fix fixed timestep and interpolation for smooth 2D movement?

[WilliamKJ]

I’ve been trying to implement a proper game loop in my 2D engine prototype, but I can’t seem to get the fixed timestep and interpolation right for smooth movement. Every time I think I’ve decoupled the update rate from the frame rate, something feels either too jittery or weirdly sped up.

[Thomas68]

I wrestled with a fixed timestep and an accumulator for weeks. It helped stabilize physics, but when frame times bloated the motion still jittered or snapped forward. I capped the delta to about 0.033s and kept render interpolation simple, which reduced the twitch a bit, but it never felt perfect in long frames.

[PaulS]

I tried fully decoupling update and render and used a consistent dt of 1/60. I looped updating while acc >= dt and then drew with an alpha based on acc/dt. In clean runs it looked smoother, but in scenes with lots of sprites the updates slipped and the motion would stall for a frame or two during big fps drops.

[ElizabethW]

Maybe the root cause isn’t the loop itself. I chased jitter for days and started wondering whether the issue is in how interpolation is applied to positions or how the camera follows the player. Is the delta being clamped?

[Hannah43]

One time I drifted into checking whether VSync or the window’s redraw timer was throwing things off. It felt off topic for a while, then I came back to the simple habit: keep the physics updates at a steady pace, render with a smoothed factor, and don’t chase every tiny frame. Still not a perfect result, but it helps me sleep at night.