About Sine and Bullet behavior.

I have bullet background and obstacles with sine behavior object. When obstacles moved left, I saw they're slower than moved right because their speed was subtracted from bullet background.

How can I fix this problem?

If you are doing what I think...

Change the sine movement from horizontal to value and add this value to the x position of your sprite. (Capx to follow)

Bit more complicated than I first thought - this method works providing the bullet speed is not too high.

test of sine movement combined with bullet. starfiels particles

if you need the bullet speed higher and still have this "sine movement wobble" then I think multiplying the sine movement when moving against the bullet movement (to counteract the bullet movement) would be the way to go...