[Guidolib-devel] Implementing Musical Time Pos to Graphical Pos mapping

[Stephane L. <le...@gr...>]

Hi Kai,


Juergen told me that you may have more time to answer some Guido
questions (: 


For the Imutus prototype I implemented a MusicalPos to GraphicalPos
mapping by directly hacking the OnDraw method of some graphic classes.
It was made the following way:


- patch the GRSingleNote and GRSingleREst methods to keep the pair
(Musical Time Pos and Graphical Pos [ x, y values]) in a list.


- for chords I find out that all notes in the chord do not have the
correct Musical Time value, i had to keep the value of the preceding
"empty" object and associate it to all notes of the chord.


- after this step, the (MusicalTimePos, GraphicalPos) list is scanned,
and the YMix,YMax values for all notes inside a system is computed.
This (YMix,YMax) value is then associated to all notes of the
corresponding system.


- a GuidoMusiclPos2GraphicalPos function  allow to retrieve the
GraphicalPos corresponding to a given  MusicalPos in the form (X, YMin,
YMax). This allows to later display a cursor at the right x position
with a correct y dimension.


During the coding i found several problems:


- it seems that there is a problem in the [system, page] data
structure.  The last system of a page does not point to its containing
page but to the next page.  Is this the expected behavior? it seems
like a bug but i was not able to find at which step it could occur.

This problem does no occur in an explicit \newPage tag is used.


It seems that this problem also explains the strange behavior of the
GuidoGetPageRTP function.


- the GuidoGetPageNum(int num, int denom) returns -1 when the given
(num, denom) values do not correspond to existing musical symbols in
the structure. 



Could you help me found the last system pointer bug? Do you have any
advice on when and how this mapping structure could be built in a
cleaner way?



Thanks in advance


Stephane 







Grame: Centre National de creation musicale

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