>"In practice I'm dividing dimensions of body (equal to viewport) and the
>centered element by 2, and subtract half of one from half of the
>other to get the offset needed to get the vertical mid-point of the
>element positioned in the vertical mid-point of viewport"
yup, clear...
>*if* (and only if) the viewport is tall enough to house the entire
container.
> If the viewport is too small for the element, I zero out margin-top so the
element stays inside viewport.
And here WAS my question:
If the browsers, automatically add scroll bars to the viewport, allowing it,
with this, to grow indefinitely, then, when or how can the viewport be too
small for the element?
I mean, each time we make the subtraction between half of the viewport with
half of the element we want to center, we will never get a negative value,
because the viewport will be always bigger then centered element, hence,
I've not understand why we have to set it to "0".
If we give a negative top margin to a element, it will get "out of range" to
the viewport. Ok.
If we force a negative top margin to go to 0, we will get the contents
visible to us on the viewport. Ok.
But I WAS not getting why we need that on a expression that seemed to never
give a negative value.
Why was I saying that the js expression "seems to never give a negative
value"? Because I have tested with this expression:
div#wrapper {
margin-top:
expression(document.documentElement.offsetHeight/2)-(parseInt(offsetHeight)/
2) +'px') ;
}
Then I have change the value of the center element to a exaggerated big
number, and then, I was surprised to see that the center element was stick
on the top, all visible, so, with margin-top 0.
But this WAS my question, not anymore, because, while I was writing this
e-mail, I've noticed that the expression above was not correct. I've
corrected the expression to this one:
div#wrapper {
margin-top:
expression((document.documentElement.offsetHeight/2)-(parseInt(offsetHeight)
/2) +'px') ;
}
And I can now see that the element gets out of range on the top of the
viewport. So I've now understand why we need to use this first line:
expression((document.documentElement.offsetHeight/2)-(parseInt(offsetHeight)
/2) <0 ? "0" .
Yupi!! :)
Thanks a lot for your reply, and for your time on this,
Regards,
Márcio
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