When to use Screen.WaitForVBL()

[sylus101]

I understand it's good to use that function to avoid certain screen glitches. Is there an exact science as to when to use it?

[Jeremysr]

I've never really used it because I always assumed DSLua called the PAlib function of it for you. But I could be wrong I guess.

In the PAlib examples there is always an "infinite loop" that the whole program runs in. At the top of this loop they put the wait for V-blank function.

The only places I've used it is for delays. A V-blank is always 1/60 of a second on the DS hardware (not sure about emulator.) So if I want a delay of 2 seconds I do this:

for i = 1, 60*2 do Screen.WaitForVBL() end

[daltonlaffs]

There are only two uses for the WaitForVBL function:

1) As jeremysr already said, for delays (there are 60 of them per second on a DS)

2) If you wait for a VBL before loading a large number of sprites consecutively, they are far less likely to 'skip-load' -- in other words, having slight delays between each sprite or two.

Other than that, I don't think it has any real uses. 

[sylus101]

Okay, sounds good.

Here's a couple of functions I like to use for delays:

function vbwait_sec(t)
  t = t * 60
  for delay=1,t do
    Screen.WaitForVBL()
  end
end

function vbwait(t)
  for delay=1,t do
    Screen.WaitForVBL()
  end
end