CODEWITHSUNDEEP
cwindowswinapi
user3542317
user3542317

Reputation: 313

What's the value of the scroll-bar-range?

I'm dealing with the mathematical logic of scroll bars in windows. To be specific I don't know what a variable means. The scroll bar logic goes like this:

 (thumb-size / scroll-bar-size) = (page-size / scroll-bar-range)

Now, I'm wondering what the scroll-bar-range is. I know what the range of a scroll bar is though. But I dont know how this helps to put that into the formula. Because we have a range from [0...n] and not a single value. We have multiple values Zero, one, two through n.

For example if I have a scrollbar range defined like this:

SCROLLINFO si;
si.nMin = 0;        // minimum value of scroll-bar-range
si.nMax = 50;       // maximum value of scroll-bar-range
si.nPage = 25;      // page-size

How would I put the range into the above formula? Assuming that the range in this case is [0..50]. I don't know if that is correct but that is what my inituition tells me.

Anyway, in this case the page-size would be 25. But what have I to substitute for the scroll-bar-range in the above formula? is it 51? That would give:

25 / 51

Thanks guys.

Upvotes: 0

Views: 438

Answers (1)

xMRi
xMRi

Reputation: 15375

The range is nMax-nMin+1! So it is 51.

In fact Setting nMin=0 nMax=50 and nPage to 25. will cause nPos to be in the range between 0 and 26! http://msdn.microsoft.com/en-us/library/windows/desktop/bb787595(v=vs.85).aspx

The reason is that if nPos (the top line) is on index 26 you have 25 lines from 26 to to number 50 on that page-.

In your sample the quotient 25/51 tells the System that the tumb area will cover 21/51 of the full (1.0) space of the scroll bar. Because the size of the thumb Shows the relative page Position in the scrollable area.

HTH

Upvotes: 1

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