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dev:notation_layout_staff_types_etc [2010/10/04 10:35]
127.0.0.1 external edit 		dev:notation_layout_staff_types_etc [2010/10/17 02:53]
jeanettewells
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- +makes life easier with [[http://www.bestessays.com.ua|essay papers]] and you will own your success!
-=====Notation layout, staff types etc===== +
- +
-[[http://sourceforge.net/mailarchive/forum.php?thread_name=200603080947.42888.ztraveler%40adelphia.net&forum_name=rosegarden-devel|Mail archive thread link]] (a long discussion about potential future changes) +
- +
-See also [[Notation editor improvement thoughts|Notation editor improvements]]. +
- +
-See also [[Score layout, not just notation layout]]. +
- +
- +
- +
-**Note: this is not a description of code actually in Rosegarden, it's part of a discussion about future work. +
- +
-That particular discussion didn't really go anywhere, but it's possible material for later.** +
- +
- +
-On Tuesday 21 Mar 2006 16:00, Michelle Donalies wrote: +
-> SingleStaff -- the traditional classical staff +
-> GrandStaff -- needs to know essentially the same stuff as +
-> SingleStaff. The only real difference is to which part (upper or lower) an event belongs. +
-> TabStaff -- normal tablature as found in books, with traditional notation above and tab lines below. +
-> CompactTabStaff -- only one part, with no traditional notation. +
-> PercussionStaff -- this is a different animal. Clefs and key sigs are completely absent. +
-> PercussionStaffLine -- like a PercussionStaff, but with only one line, which represents an "instrument" +
-> ChordStaff +
- +
-A good summary, thanks. +
- +
-So, how do these differ? +
- +
-The first thing that strikes me (given the recent thread, and my +
-comments in it) is that there are not many fundamental differences +
-between how these different staffs handle horizontal layout. +
- +
-I clipped some of your descriptions above, but I didn't see anything +
-substantial in there that couldn't be explained as "one staff shows +
-event type X but the other one doesn't". Since a staff already gets to +
-choose what events it selects from the underlying segment (via +
-Staff::wrapEvent), this suggests that nothing outside of the staff +
-itself should actually care whether a staff has (say) clefs and keys in +
-it or not. Time signature and bar lines (which are not events) are a +
-different matter, but it ought still to be a simple question of testing +
-a flag to determine whether to lay them out or not, for any staff type. +
- +
-However, there are certainly differences in implementation in +
-Rosegarden, many of which are caused by the current implementation of +
-NotationHLayout doing more than it should. These are examples of +
-things that appear to me to be really different and potentially +
-problematic: +
- +
-1. Vertical layout. NotationVLayout could certainly be done by a staff +
-type rather than a layout class. Different staffs have quite different +
-vertical layout techniques and there's no call to reconcile between +
-them. (btw I'm also not sure that the NotationView's current code to +
-position the staffs on the page will do the right thing if the staffs +
-are of unequal heights.) +
- +
-2. Accidentals. The current HLayout manages which of these are shown +
-and how they are spaced based on the current clef and key, which of +
-course may differ or disappear in other staff types. This is confined +
-to the HLayout::scanStaff area and would be easy to suppress, but it +
-would not be so tidy a thing to do as just suppressing the appearance +
-of clefs and keys for example. +
- +
-3. The HLayout does several things which are not strictly its job at +
-all, such as assigning stem lengths for beamed groups. (Well, it +
-doesn't do these things itself, but it does cause them to happen.) It +
-does so just because it's in the right place: after vertical layout but +
-before horizontal positioning is finalised. A more correct +
-implementation would probably have an intermediate pass between +
-vertical and horizontal layout for these. This is again a fairly small +
-amount of code in the HLayout class, but it's untidy. +
- +
-4. Properties calculated in the layout phase are stored in the Event +
-object, with names unique to the NotationView instance so that +
-different views can do different layouts (e.g. in different sizes, or +
-one in a page layout and another in a linear one). However, these are +
-View-specific, not Staff-specific. If it became possible to have the +
-same event on more than one staff in the same view at the same time, +
-this would break. +
- +
-I don't see any obvious disadvantages to refactoring 1, and I think 2 +
-and 3 are both candidates for things that could usefully be refactored +
-to improve the code even if we had no intention of adding any more +
-staff types in the first place, although there may be some tricky +
-details. Also I'm not especially happy with the way that beamed groups +
-and tuplets are handled anyway. (Our reconciliation of simultaneous +
-events on different staffs is quite good though, which is partly why I +
-took badly to your observation that doing anything better than +
-selecting the widest minimum spacing was "overkill" -- it isn't at all, +
-it makes a big difference and we do far better than that now.) +
- +
-> This still doesn't solve the basic disconnect with a staff representing a Segment rather than a Track. +
- +
-If you're thinking about that, then you might perhaps also think about +
-multi-voice staffs, for which the general underlying thought has been +
-that the user may choose optionally to show different segments (even on +
-different tracks) as different voices on the same staff, via some sort +
-of part arranger interface. Most of the basic layout code supports +
-this already. +
- +
-[ separate email, actually earlier ] +
- +
-The original idea for the HLayout and VLayout classes was to use +
-something like the "visitor" design pattern to separate out the layout +
-logic from the staff container or the low-level drawing functions (both +
-of which are either in, or invoked from, the staff class). This is not +
-so much because you might want to use more than one type of layout for +
-a given staff, as to keep the layout-related reasoning separate for +
-code management purposes. +
- +
-The fact that the things we want to do next aren't easily possible using +
-the current classes implies that something is wrong, of course, but I'm +
-not sure that making the staff class so much more complicated is a good +
-idea on the road to fixing it. +
- +
-Attached is a "whiteboard diagram" I sketched on paper (you can gather +
-that I'm still not getting much time at the computer to think about +
-these things at the moment). This shows the stages of the layout +
-procedure (from memory, so doubtless some omissions) with the classes +
-that currently carry them out. Start reading at top-left; the vertical +
-division is broadly into single-staff layout at top, multi-staff +
-reconcile and layout etc in the middle, drawing at the bottom. +
- +
-So, for each of the steps on this diagram, which is the most appropriate +
-class to do the work? Assuming for the moment that there's no +
-obligation to use the existing class structure (there is an obligation +
-effectively to use the existing _code_, but it can be rearranged at +
-will). It seems that the existing classes mostly do multiple tasks +
-that are not necessarily closely related but that share some of the +
-same data or domain knowledge (e.g. the HLayout class doing things with +
-beamed groups and accidentals), and there may well be a case for +
-pulling these things out into more than one class rather than just +
-changing which of the existing classes they go into. +
- +
-{{:whiteboard.jpg|}} +
  
 
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