I am trying to build a custom-scrollbar with winapi

To get Thumb length :

B / A = D / C

D = C * B / A

All fine so far. but struggling to find the Thumb position

Given an (viewport) offset, how to get the thumb offset? Or any suggestions?

CodePudding user response：

First, your thumb size calculation contains an error - rearranging valid proportion A / B = C / D, thumb size is D = C * B / A, not D = C * A / B. Regarding offset calculation, proportion can be constructed in a similar way since track C represents whole content A and thumb offset F represents viewport offset E. So, A / C = E / F, from which, rearranging, we get F = E * C / A.