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mscore3.txt
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====================================================================
Remarks for MuseScore Version 3
design goals/changes
====================================================================
- Optimize horizontal layout by allowing overlapping segments.
- Compute an outline (Shape) for every Staff/Segment.
- Use the outline to compute the minimum distance between Segments.
- this also avoids collisions between Lyrics and ChordNames
- Automatically increase vertical space between staves to avoid collisions.
- Use the segment shapes to compute the minimum distance between staves.
Use the minimum distance if its bigger than the style distance;
- Implement a way to (re-)layout only the modified part of the score.
A reorganization of layout is needed for this. Layout should work in one pass in
an incremental way.
The pattern to trigger incremental layout is:
score->startCmd();
...
score->setLayout(tick1); // tick position of score change
...
score->setLayout(tickn); // another change at a different position
...
score->endCmd();
setLayout(int tick) records the min+max value of all calls and feeds it
to score->doLayoutRange(int minTick, int maxTick);
- Do not allow more than one System on a line. In 2.x a horizontal box splits
a line into two systems. In 3.x a horizontal box is handled as a special measure.
This simplifies page layout a lot.
- System bar lines are moved into measures in a special segment type "BeginBarLine".
- Do not undo/redo add/removal of "created" elements.
- It speeds up doLayout() and consumes less memory.
In 2.x all Segments changes must be on the undo/redo stack to keep the history
consistent, This was necessary as Segments were referring to
previous/next segments to find the proper insertion point.
In 3.x Undo knows were to (re-)insert Segments by only checking type and tick
position.
- evaluate the possibility of implementing "Continuous View" as a real "view" change
without changing the score (no undo/redo change)
- remove pre 2.0 compatibility
====================================================================
New Features
====================================================================
Timewise insert/delete notes/rests
-----------------------------------
- Ctrl+Shift+[cdefg]
Insert note with current duration.
This increases the duration of the actual measure independent of the
current time signature making it an irregular measure.
- Ctrl + left mouse button in note entry mode
Inserts note/rest with current duration
- Ctrl+Del
Removes the selected Chord/Rest decreasing the duration of the measure.
Extend this to selection ranges.
- drop barline
This inserts a barline into the current measure or changes the current barline.
- ctrl + drop barline
Splits the current measure at the new barline.
- ctrl + delete barline
This joins the current measure with the next measure.
- show irregular measures
This displays a "+" or "-" in the upper right corner of a measure if the measure
length is different from the current time signature.
Functions which may be removed:
- split measure: replaced by dropping a barline
- join measure: replaced by deleting a barline
- adjusting the actual measure lenght in measure properties; this
can be achieved by inserting/deleting notes/rests in the measure.
- delete measure timewise: replaced by Ctrl+Del of selection ranges
Palette handling
-------------------------------
- shift+drag allows to move a palette element in the palette
- ctrl+drag is drag operation with special semantic
====================================================================
Programming Style Changes in MuseScore 3
====================================================================
* Instead of
if (e->type() == Element::Type::Chord)
...
write
if (e->isChord())
...
This is shorter and easier to read. Similar
if ((s.segmentType() == Segment::Type::ChordRest))
...
can be written as
if (s.isChordRestType())
...
* Use safer type conversion: instead of
Chord* chord = static_cast<Chord*>(e);
write
Chord* chord = toChord(e);
This adds an Q_ASSERT to make sure e is really a Chord().
* Prefer vector container over list:
- Instead of QList use QVector or even better std::vector if possible.
* Prefer stl style over Qt style when using container:
- use list.push_back(xx) instead of list.append(xx) or
- use list.empty() instead of list.isEmpty()
- etc.
(see https://marcmutz.wordpress.com/effective-qt/containers/)
Caution when replacing Qt container with stl container as the semantic
may be different. Especially in a "for (xxx : yyy)" loop the Qt container
is copied (copy on write) and the stl container not. That means that you can modify a
Qt container (inserting/deleting elements) in this for loop. This will usually not
work for a stl container.
* In iterating a SegmentList instead of
for (Segment* s = segments->first(); s; s = s->next())
...
you can write
for (Segment& s : segments)
...
* enums
Some scoped enums can be replaced by classes. Example:
class Direction {
...
public:
enum _Direction { AUTO, UP, DOWN };
...
};
Goal is to allow
- allow type conversion (to QVariant for example)
- add conversion to/from string for use in Xml::read(...)/Xml::write(xxx)
- export to qml scripting
Drawbacks:
- forward declaration is not possible as for c++11 "enum class"
- the enum _Direction is a different type than Direction; which sometimes
require a static_cast
This is somehow experimental.
* debug messages
- use qWarning(), qCritical() and qFatal()
- if debug messages are used, it should be possible to switch them off and they
should be removed in release mode
- don't use qDebug(), instead use a log category and call qCDebug(logCategory, ...)
(see undo.h undo.cpp for example usage)
TODO: check if they can be removed in system mode
====================================================================
some rules
====================================================================
Layout
- After loading a score, the score data can only be modified in a "undo" function during editing.
The score is "dirty" if there is an undo stack entry.
- Flags/data which describe what kind of relayout/update the score needs are collected in
Score->CmdState. They can only be set in an "undo" function.
Score File
- "created" elements are not written out into the score file. For example bar lines are usually created
by layout. They are marked as created and therefore do not appear in the score file.
- Element properties are only written if they differ from their default value which usually is the
style value if they are styled.
====================================================================
Implementation Details
====================================================================
Measure layout
A measure is layouted in four different contexts:
- first measure in a system
- the measure is prepended by a system header
- last measure in a system
- the measure has a system trailer
- in the middle of a system
- is the only measure in a system
- the measure has a system header and a system trailer
BarLine handling
A measure can have four kind of barlines, contained in a special typed Segment:
- BeginBarLine
this barline is also called the "systemic barline"
- automatically created for every System
- a BarLine can be dropped on a horizontal frame which adds
a BeginBarLine to the next measure
- overrides the EndBarLine of a previous measure in the system
- StartRepeatBarLine
- after a horizontal frame it overrides a BeginBarLine
- is prepended by a system header if in the first system measure
- sets the _repeatStart measure flag
- BarLine
- is in the middle of a measure and has no semantic (repeat etc.)
(tick > start tick of measure and tick < end tick of measure)
- EndBarLine
- is created automatically
- maybe not the last Segment in a Measure (cautionary elements can follow)
Ottava
Ottavas have no placement style. Placement depends on the ottava subtype and is hardcoded.
Dynamics
Default vertical reference position for Placement "below" (dynamicPosBelow = 0.0) is the last
staff line + text line height.
Styles & Properties
There is a connection between style values and property values as some properties
can be styled. The StyleIdx of a property style can be found by calling
StyleIdx Element::getPropertyStyle(P_ID)
If the property has no style, then StyleIDx::NOSTYLE is returned.
A property can have different style values depending on the element type.
====================================================================
Known Issues
====================================================================
* tablature not tested, has likely regressions
* some scripting interface functions are commented out
* horizontal layout mode not working right