change x text position dinamically when speed>0

[kessenza]

Using method video.add_text and speed > 0 (and in particular when cycle=false) x is used only as initial value but then an internal x is used to scroll text from right to the left. But when the text goes out and we, for instance, want to change it (to show a different info text) then the internal x stays out of the screen and there is no way to bring it back to the right

[smimram]

For this one, let's first discuss this here. I fear that if I add this the code will become clumsy and moreover, we will never be able to cover all possible cases of needs with video.add_text.

However, I have good news: you can achieve what you want in Liquidsoap, by programming your own advanced x parameter. The x function is called at every frame, you can then simply return the value of a reference, updated in a way which suits your needs. You can draw inspiration from the implementation of video.add_text itself: https://github.com/savonet/liquidsoap/blob/main/src/libs/video.liq#L301

Typically for a scrolling you would do something like:

fps = video.frame.rate()
r = ref(0)
speed = 100 # scrolling speed

def x()
  x := !x + speed / fps
  !x
end
video.add_text(x, "text", main_source)

and you can easily add more logic in order to detect when the boundary is reached etc.

[kessenza]

Just to be sure (because I am little weak on ls scripting language). Do you mean ? :

fps = video.frame.rate()
r = ref(0)
speed = 100 # scrolling speed

def x()
  r := !r + speed / fps
  !r
end

Yes this solves all the possible cases together wtih #2621
The only little thing is that in this way (in particular when) cycling on the opposite way ( r := !r - speed / fps), it's not easy to detect when text goes out of the screen because you have to compute string.length(text) * pixel_by_char

Anyway it works. Thanks!