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This review has been submitted with commit c4386adf8963c65e5bee5dedb8536f1e6594fcb1 by Sam Lade to branch master. - Commit Hook On May 13, 2012, 11:42 p.m., Alexander Potashev wrote: > > ----------------------------------------------------------- > This is an automatically generated e-mail. To reply, visit: > http://git.reviewboard.kde.org/r/104935/ > ----------------------------------------------------------- > > (Updated May 13, 2012, 11:42 p.m.) > > > Review request for Amarok, Leo Franchi and Rick W. Chen. > > > Description > ------- > > The former scrolling algorithm was to scroll text continuously > while playing a song. In this case the first lines of lyrics hide > very quickly - often before they are sung. > > Again, with the old algorithm the scrollbar position is 0 at the > beginning of the song (0:00), and it reaches the maximum possible > position exactly when the song ends. > > The new algorithm tries to keep the currently "played" line > at center of the Lyrics applet window. To achieve this, we > target scrollbar position to be (-pageStep/2) at the beginning > of the song (0:00), and to reach position (maximum + pageStep/2) > exactly when the song ends. > > `pageStep` is the height of Lyrics applet window expressed in the > units used by the scrollbar. Therefore `pageStep/2` is an offset > that can be added/substracted to move down/up by half a page in > the Lyrics applet. > > Here is a formula to transform a scrollbar position used in the old > algorithm to the scrollbar position when the new algorithm is used: > > new_pos = pos / maximum * (maximum + pageStep) - pageStep / 2 > > We make the following changes to the algorithm: > > 1. Multiply by (maximum + pageStep) instead of `maximum` to fulfill > the multiplication factor from the above formula. > > 2. Additionally, substract `pageStep/2`, as defined by the above > formula. > > 3. Avoid using floating point math (the "double" data type) to improve > performance. > > 4. Re-read the current position of the scrollbar when saving > `oldSliderPosition`, because scrollbar positions calculated using > the above formula may be out of the allowed range of the scrollbar > and "truncated", i.e. adjusted to fit the scrollbar range. > When truncated, `vbar->value()` differs from `newSliderPosition`. > > > Diffs > ----- > > src/context/applets/lyrics/LyricsApplet.cpp 9720db0 > > Diff: http://git.reviewboard.kde.org/r/104935/diff/ > > > Testing > ------- > > Works as expected. > > > Thanks, > > Alexander Potashev > >
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