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<p>
<a name="Visibility-and-color-of-objects"></a>
Next: <a rel="next" accesskey="n" href="Size-of-objects.fr.html#Size-of-objects">Size of objects</a>,
Up: <a rel="up" accesskey="u" href="Appearance-of-objects.fr.html#Appearance-of-objects">Appearance of objects</a>
<hr>
</div>
<h4 class="subsection">4.3.1 Visibility and color of objects</h4>
<p>In the educational use of music we might wish to print a score
with certain elements omitted as an exercise for the student,
who is required to supply them. As a simple example,
let us suppose the exercise is to supply the missing bar lines
in a piece of music. But the bar lines are normally inserted
automatically. How do we prevent them printing?
<p>Before we tackle this, let us remember that object properties
are grouped in what are called <em>interfaces</em> – see
<a href="Properties-found-in-interfaces.fr.html#Properties-found-in-interfaces">Properties found in interfaces</a>. This is simply to
group together those properties that are commonly required
together – if one of them is required for an object, so are
the others. Some objects then need the properties in some
interfaces, others need them from other interfaces. The
interfaces which contain the properties required by a
particular grob are listed in the IR at the bottom of the
page describing that grob, and those properties may be
viewed by looking at those interfaces.
<p>We explained how to find information about grobs in
<a href="Properties-of-layout-objects.fr.html#Properties-of-layout-objects">Properties of layout objects</a>. Using the same approach,
we go to the IR to find the layout object which prints
bar lines. Going via <em>Backend</em> and <em>All layout objects</em>
we find there
is a layout object called <code>BarLine</code>. Its properties include
two that control its visibility: <code>break-visibility</code> and
<code>stencil</code>. Barline also supports a number of interfaces,
including the <code>grob-interface</code>, where we find the
<code>transparent</code> and the <code>color</code> properties. All
of these can affect the visibility of bar lines (and, of course,
by extension, many other layout objects too.) Let's consider
each of these in turn.
<h4 class="subheading">stencil</h4>
<p><a name="index-stencil-property-372"></a>
This property controls the appearance of the bar lines by specifying
the symbol (glyph) which should be printed. In common
with many other properties, it can be set to print nothing by
setting its value to <code>#f</code>. Let's try it, as before, omitting
the implied Context, <code>Voice</code>:
<blockquote>
<pre class="verbatim">
{
\time 12/16
\override BarLine #'stencil = ##f
c4 b8 c d16 c d8 |
g, a16 b8 c d4 e16 |
e8
}
</pre>
<p>
<a href="../23/lily-62cf82cd.ly">
<img align="middle"
border="0" src="../23/lily-62cf82cd.png" alt="[image of music]">
</a>
</p>
</blockquote>
<p>The bar lines are still printed. What is wrong? Go back to the
IR and look again at the page giving the properties of BarLine.
At the top of the page it says “Barline objects are created
by: Bar_engraver”. Go to the <code>Bar_engraver</code> page.
At the bottom
it gives a list of Contexts in which the bar engraver operates.
All of them are of the type <code>Staff</code>, so the reason the
<code>\override</code> command failed to work as expected is because
<code>Barline</code> is not in the default <code>Voice</code> context.
If the context
is specified wrongly, the command simply does not work. No
error message is produced, and nothing is logged in the log
file. Let's try correcting it by adding the correct context:
<blockquote>
<pre class="verbatim">
{
\time 12/16
\override Staff.BarLine #'stencil = ##f
c4 b8 c d16 c d8 |
g, a16 b8 c d4 e16 |
e8
}
</pre>
<p>
<a href="../4e/lily-f9ac0581.ly">
<img align="middle"
border="0" src="../4e/lily-f9ac0581.png" alt="[image of music]">
</a>
</p>
</blockquote>
<p>Now the bar lines have vanished.
<h4 class="subheading">break-visibility</h4>
<p><a name="index-break_002dvisibility-property-373"></a>
We see from the <code>BarLine</code> properties in the IR that the
<code>break-visibility</code> property requires a vector of three
booleans.
These control respectively whether bar lines are printed at
the end of a line, in the middle of lines, and at the beginning
of lines. For our example we want all bar lines to be suppressed,
so the value we need is <code>'#(#f #f #f)</code>.
Let's try that, remembering
to include the <code>Staff</code> context. Note also that in writing
this value we have <code>#'#</code> before the opening bracket.
The <code>'#</code> is required as part of the value to introduce a
vector, and the first <code>#</code> is required, as always, to precede
the value itself in the <code>\override</code> command.
<blockquote>
<pre class="verbatim">
{
\time 12/16
\override Staff.BarLine #'break-visibility = #'#(#f #f #f)
c4 b8 c d16 c d8 |
g, a16 b8 c d4 e16 |
e8
}
</pre>
<p>
<a href="../bd/lily-77d8b3d7.ly">
<img align="middle"
border="0" src="../bd/lily-77d8b3d7.png" alt="[image of music]">
</a>
</p>
</blockquote>
<p>And we see this too removes all the bar lines.
<h4 class="subheading">transparent</h4>
<p><a name="index-transparent-property-374"></a>
We see from the properties specified in the <code>grob-interface</code>
page in the IR that the <code>transparent</code> property is a boolean.
This
should be set to <code>#t</code> to make the grob transparent.
In this next example let us make the time signature invisible
rather than the bar lines.
To do this we need to find the grob name for the time signature.
Back to
the ‘All layout objects’ page in the IR to find the properties
of the <code>TimeSignature</code> layout object. This is produced by
the <code>Time_signature_engraver</code> which you can check also lives
in the <code>Staff</code> context and also supports the
<code>grob-interface</code>. So the command to make the time signature
transparent is:
<blockquote>
<pre class="verbatim">
{
\time 12/16
\override Staff.TimeSignature #'transparent = ##t
c4 b8 c d16 c d8 |
g, a16 b8 c d4 e16 |
e8
}
</pre>
<p>
<a href="../94/lily-af1cfd91.ly">
<img align="middle"
border="0" src="../94/lily-af1cfd91.png" alt="[image of music]">
</a>
</p>
</blockquote>
<p class="noindent">The time signature is gone, but this command leaves a gap where
the time signature should be. Maybe this is what is wanted for
an exercise for the student to fill it in, but in other
circumstances a gap might be undesirable. To remove it, the
stencil for the time signature should be set to <code>#f</code>
instead:
<blockquote>
<pre class="verbatim">
{
\time 12/16
\override Staff.TimeSignature #'stencil = ##f
c4 b8 c d16 c d8 |
g, a16 b8 c d4 e16 |
e8
}
</pre>
<p>
<a href="../72/lily-9905bb54.ly">
<img align="middle"
border="0" src="../72/lily-9905bb54.png" alt="[image of music]">
</a>
</p>
</blockquote>
<p class="noindent">and the difference is obvious: setting the stencil to <code>#f</code>
removes the object entirely; making the object <code>transparent</code>
leaves it where it is, but makes it invisible.
<h4 class="subheading">color</h4>
<p><a name="index-color-property-375"></a>
Finally let us try making the bar lines invisible by coloring
them white. (There is a difficulty with this in that the
white bar line may or may not blank out the staff lines where
they cross. You may see in some of the examples below that this
happens unpredictably. The details of why this is so and how to
control it are covered in <a name="index-Painting-objects-white-376"></a><a href="../lilypond/Painting-objects-white.fr.html#Painting-objects-white">Painting objects white</a>. But at
the moment we are learning about color, so please just accept this
limitation for now.)
<p>The <code>grob-interface</code> specifies that the
color property value is a list, but there is no
explanation of what that list should be. The list it
requires is actually a list of values in internal units,
but, to avoid having to know what these are, several ways
are provided to specify colors. The first way is to use one
of the ‘normal’ colors listed in the first table in
<a name="index-List-of-colors-377"></a><a href="../lilypond/List-of-colors.fr.html#List-of-colors">List of colors</a>. To set the bar lines to white
we write:
<blockquote>
<pre class="verbatim">
{
\time 12/16
\override Staff.BarLine #'color = #white
c4 b8 c d16 c d8 |
g, a16 b8 c d4 e16 |
e8
}
</pre>
<p>
<a href="../36/lily-5d1ecfa9.ly">
<img align="middle"
border="0" src="../36/lily-5d1ecfa9.png" alt="[image of music]">
</a>
</p>
</blockquote>
<p class="noindent">and again, we see the bar lines are not visible. Note that
<em>white</em> is not preceded by an apostrophe – it is not
a symbol, but a <em>function</em>. When called, it provides
the list of internal values required to set the color to
white. The other colors in the normal list are functions
too. To convince yourself this is working you might like
to change the color to one of the other functions in the
list.
<p><a name="index-color_002c-X11-378"></a><a name="index-X11-colors-379"></a>
The second way of changing the color is to use the list of
X11 color names in the second list in <a name="index-List-of-colors-380"></a><a href="../lilypond/List-of-colors.fr.html#List-of-colors">List of colors</a>.
However, these must be preceded by another function, which
converts X11 color names into the list of internal values,
<code>x11-color</code>, like this:
<blockquote>
<pre class="verbatim">
{
\time 12/16
\override Staff.BarLine #'color = #(x11-color 'white)
c4 b8 c d16 c d8 |
g, a16 b8 c d4 e16 |
e8
}
</pre>
<p>
<a href="../8d/lily-4ec6a6e7.ly">
<img align="middle"
border="0" src="../8d/lily-4ec6a6e7.png" alt="[image of music]">
</a>
</p>
</blockquote>
<p class="noindent">Note that in this case the function <code>x11-color</code> takes
a symbol as an argument, so the symbol must be preceded by
an apostrophe and the two enclosed in brackets.
<p><a name="index-rgb-colors-381"></a><a name="index-color_002c-rgb-382"></a>
There is yet a third function, one which converts RGB values into
internal colors – the <code>rgb-color</code> function. This takes
three arguments giving the intensities of the red, green and
blue colors. These take values in the range 0 to 1. So to
set the color to red the value should be <code>(rgb-color 1 0 0)</code>
and to white it should be <code>(rgb-color 1 1 1)</code>:
<blockquote>
<pre class="verbatim">
{
\time 12/16
\override Staff.BarLine #'color = #(rgb-color 1 1 1)
c4 b8 c d16 c d8 |
g, a16 b8 c d4 e16 |
e8
}
</pre>
<p>
<a href="../59/lily-26b4a44d.ly">
<img align="middle"
border="0" src="../59/lily-26b4a44d.png" alt="[image of music]">
</a>
</p>
</blockquote>
<p>Finally, there is also a grey scale available as part of the
X11 set of colors. These range from black, <code>'grey0'</code>,
to white, <code>'grey100</code>, in steps of 1. Let's illustrate
this by setting all the layout objects in our example to
various shades of grey:
<blockquote>
<pre class="verbatim">
{
\time 12/16
\override Staff.StaffSymbol #'color = #(x11-color 'grey30)
\override Staff.TimeSignature #'color = #(x11-color 'grey60)
\override Staff.Clef #'color = #(x11-color 'grey60)
\override Voice.NoteHead #'color = #(x11-color 'grey85)
\override Voice.Stem #'color = #(x11-color 'grey85)
\override Staff.BarLine #'color = #(x11-color 'grey10)
c4 b8 c d16 c d8 |
g, a16 b8 c d4 e16 |
e8
}
</pre>
<p>
<a href="../78/lily-1319851f.ly">
<img align="middle"
border="0" src="../78/lily-1319851f.png" alt="[image of music]">
</a>
</p>
</blockquote>
<p class="noindent">Note the contexts associated with each of the layout objects.
It is important to get these right, or the commands will not
work! Remember, the context is the one in which the appropriate
engraver is placed. The default context for engravers can be
found by starting from the layout object, going from there to
the engraver which produces it, and on the engraver page in the
IR it tells you in which context the engraver will normally be
found.
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Next: <a rel="next" accesskey="n" href="Size-of-objects.fr.html#Size-of-objects">Size of objects</a>,
Up: <a rel="up" accesskey="u" href="Appearance-of-objects.fr.html#Appearance-of-objects">Appearance of objects</a>
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