Updated the Grid & Snap page.

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<h2> What is “Snap” and “Grid”?</h2>
<figure class="left">
<img src="/images/toolbar-grid.png" alt="Editor toolbar's grid">
<figure>
<img src="/images/toolbar-grid.png" alt="Snap & Grid">
<figcaption>
Editor toolbar's grid.
Snap & Grid
</figcaption>
</figure>
<p>
“Snap” will cause drags and other mouse-driven operations to jump to
positions determined by the nearest snap setting. Snap can be set to
multiple options: markers, region start/ends, and the grid (those
are all enabled by default. change them in prefs).
</p>
<p>
Grid can be enabled, and it will draw lines at selected intervals;
which can be musical, like 16th notes, or can be timecode based
(minutes and seconds). You can leave the Grid enabled, but snap
disabled, if you just want to see the lines but not snap to them.
</p>
<p>
For example: if the Grid is set to “beats” and Snap-to-grid is
enabled, then any operations such as split, paste, or range-select
will happen exactly on a beat, according to the musical timeline and
tempo.
</p>
<p>
Alternatively, you can leave “Snap” enabled (so your mouse actions
can snap to Markers, or region edges) but disable the Grid.
</p>
<h2>A Warning, of sorts</h2>
<p class="warning">
The grid consist of lines running vertically in the edit canvas. If
you zoom too far out, you might see a coarser grid than you
expect. Ardour tries not to show “too many” or “too few” grid lines
depending on the zoom level. You might find that items snap in-between
the grid lines sometimes. Thats expected behavior. If you cant see
or snap to the grid youd like to use, you may have to zoom in or out.
</p>
<h2>About Snapping</h2>
<h2 id="grid_controls-snap">Snap</h2>
<p>
There are two ways to think about aligning material. The first and
most obvious one is where an object's position is clamped to the
snap positions. In Ardour, this is called <dfn>absolute snap</dfn>
and is commonly used when working with sampled material where audio
begins exactly at the beginning of a file, note or region.
<dfn>Snap</dfn> will cause region drags and other mouse-driven
operations to jump to positions determined by the nearest snap
setting when the mouse is close enough to this snap point. Snapping
is sometimes (improperly) referred to as magnetism.
</p>
<p>
The Snap options are set in the <a
href="@@preferences#preferences-editor-snap">Preferences</a>. Those
include the Snap Threshold which determines how close the mouse has
to be to a snap anchor to induce a snap, and the snap anchors
themselves, among:
</p>
<ul>
<li>Markers</li>
<li>Region Sync points</li>
<li>Region Starts</li>
<li>Region Ends</li>
<li>Grid.</li>
</ul>
<h2 id="grid_controls-grid">Grid</h2>
<p>
The <em>Grid</em> helps visually placing items in time. It will draw
lines at selected intervals as chosen in the drop-down selector.
Musical grid settings (<em>Bar</em> to <em>Sextuplets</em>) obviously
depend on the <a href="@@tempo-and-meter">tempo and meter</a>, so
changing the tempo or meter will rescale the grid, while absolute grid
settings (<em>Timecode</em>, etc&hellip;) won't be affected.
</p>
<p class="note">
A word about time signature in this context: a time signature
consists of 2 numbers. The upper one determines how many beats are in
a bar, the lower one, what division of a note a beat represents (e.g.
: <em>4</em> stands for a quarter note). At e.g. 80 <abbr
title="beats per minute">bpm</abbr>, one beat lasts 1/80th min, so
0.75 sec. If the time signature is 3/4, there are 3 beats in a bar so
a bar lasts for 3 &times; 0.75 = 2.25 sec. Choosing <em>1/8 Note</em>
as the grid setting will draw grid lines every 0.75 &divide; 1/4
&times; 1/8 = 0.375 sec.
</p>
<p>
The second, <dfn>relative snap</dfn>, is used when an object's
position relative to the snap positions is important. In music, this
allows to move objects around without changing the "feel" (or
timing) of a performance.
</p>
<p>
Absolute snap is the default method of snapping in Ardour.
</p>
<p>
While dragging objects, pressing the absolute snap modifier key(s) switches
from absolute to relative snap.
</p>
<p>
The snap can also be entirely disabled by using the snap modifier (see below).
</p>
<p>
Note that in relative snap mode the reference point is taken to be the distance
to the nearest grid line.
</p>
<p>
Note also that when an object lies exactly on a grid line, there will be no
difference between relative and absolute snap modes.
</p>
<p>
The relative snap and snap modifiers (along with other modifier keys) may be set
in <kbd class="menu">Edit &gt; Preferences &gt; User Interaction</kbd>
</p>
<p>
For common use patterns, it is recommended to assign a unique key for one
snap modifier and two keys for the other in such a way that they share an
otherwise unused key. For example, the snap modifier may be chosen to be the
<kbd class="mod2n"></kbd> key and the relative snap modifier to be the <kbd
class="mod2n"></kbd> and <kbd class="mod4n"></kbd> keys.
</p>
<h2>Snap Modes</h2>
<p>
Using the above modifications, Ardour supports three different modes of snapping
to the grid:
</p>
<table class="dl">
<tr><th><kbd class="menu">No Grid</kbd></th>
<td>disables the grid. All objects move freely in this mode.</br>
In <kbd class="menu">No Grid</kbd> mode, the grid may be temporarily activated
by pressing the snap modifier (for absolute snap) or switch to relative snap
by pressing the relative snap modifier.</td></tr>
<tr><th><kbd class="menu">Grid</kbd></th>
<td>activates normal snapping. All positions of objects snap to the grid. (See
<a href="#gridunits">Grid Units</a> below to change the grid).
Moving an object in "Grid"-mode, does not change its position until
the mouse is far enough for the object to reach the next grid line.</br>
To maintain an objects' position relative to the grid line, the "snap relative"
modifier can be used. When holding down this
modifier during a drag, the dragged object will jump while maintaining its
original distance from the line.</br>
New objects will always be created at grid
points.</br>
Holding down the snap modifier will disable the current grid
setting and allow moving the object freely.</td></tr>
<tr><th><kbd class="menu">Magnetic</kbd></th>
<td>is a less strict type of snapping. Objects can still be moved to any
position, but positions close to the relative or absolute grid points will snap.
In order to move an object very close to a snap point, it may be necessary to
zoom in to prevent snapping to that point, or to use the snap modifier to
disable snap completely.</br> As with Grid mode, the snap modifier will disable
snap completely while the absolute snap modifier will move the "notch" of
Magnetic snap to the grid lines.</td></tr>
</table>
<h2>Syncing Regions to the Grid</h2>
<p>
By default, a region's beginning will be used as the reference for both types of
snapping, this behaviour can be changed by setting a <dfn>sync point</dfn>
in the region, by selecting the region(s) and pressing <kbd>V</kbd>. This will set the
sync point to the current <a href="@@edit-point-control">edit point</a>.
</p>
<h2 id="gridunits">Grid Units</h2>
<p>
The selector next to the grid mode selector defines the size of the grid
elements. The grid can be set to several different units:
</p>
<table class="dl">
<tr><th><kbd class="menu">CD Frames</kbd></th>
<td>A CD Frame is 1/75th of a second. Snapping to CD Frames (using absolute snap) can be used to avoid issues with CD track lengths.</td></tr>
<tr><th><kbd class="menu">Timecode Frames/Seconds/Minutes</kbd></th>
<td>The duration of a frame depends on the timecode settings for the session.</td></tr>
<tr><th><kbd class="menu">Seconds/Minutes</kbd></th>
<td>These are absolute time units, unaffected by sample rate or timecode settings</td></tr>
<tr><th><kbd class="menu">Beats/N</kbd></th>
<td>Set the grid to units of 1/N beats, where N can be 128, 64, 32, 16, 8, 7, 6, 5, 4, 3, 2. The duration of a grid unit will depend on the tempo and meter in effect at that point in the timeline.</td></tr>
<tr><th><kbd class="menu">Beats</kbd></th>
<td>Set the grid to whole beats. The duration of a grid unit will depend on the tempo and meter in effect at that point in the timeline.</td></tr>
<tr><th><kbd class="menu">Bars</kbd></th>
<td>Set the grid to whole bars. The duration of a grid unit will depend on the tempo and meter in effect at that point in the timeline.</td></tr>
<tr><th><kbd class="menu">Markers</kbd></th>
<td>The grid lines are the markers.</td></tr>
<tr><th><kbd class="menu">Region Starts</kbd></th>
<td>The grid lines are constructed from region start points (see below).</td></tr>
<tr><th><kbd class="menu">Region Ends</kbd></th>
<td>The grid lines are constructed from region end points (see below).</td></tr>
<tr><th><kbd class="menu">Region Syncs</kbd></th>
<td>The grid lines are constructed from region sync points.</td></tr>
<tr><th><kbd class="menu">Region Bounds</kbd></th>
<td>The grid lines are constructed from region start or end points.</td></tr>
</table>
<p>
To use Region starts/ends/syncs/bounds as snap choices, it is necessary to have either:
The grid density can be either based on musical time:
</p>
<ul>
<li><em>No</em> tracks selected, which means that Ardour snaps to regions on any
track, or </li>
<li>Several tracks selected, which means that Ardour only snaps to regions on
those selected tracks.</li>
<li><em>No Grid</em>: hides the Grid</li>
<li><em>Bar</em>: shows one grid line per bar (e.g, in 4/4 at 120bpm, one line every 2 seconds)</li>
<li><em>1/4</em>: shows one grid line per quarter bar, or 4 grid lines per bar (e.g, in 4/4 at 120bpm, one line every .5 seconds)</li>
<li><em>...</em></li>
<li><em>1/128</em>: shows one grid line per 128<sup>th</sup> bar, or 128 grid lines per bar</li>
<li><em>Triplets</em>: groups the ternary divisions of time:
<ul>
<li><em>1/3 (8th triplet)</em>: shows one grid line per third bar</li>
<li><em>...</em></li>
<li><em>1/24 (64th triplet)</em>: shows one grid line per 24<sup>th</sup> bar</li>
</ul>
</li>
<li><em>Quintuplets</em>: groups the 1/5<sup>th</sup> divisions of time:
<ul>
<li><em>1/5 (8th quintuplet)</em>: shows one grid line per fifth bar</li>
<li><em>...</em></li>
<li><em>1/20 (32th quintuplet)</em>: shows one grid line per 20<sup>th</sup> bar</li>
</ul>
</li>
<li><em>Septuplets</em>: groups the 1/7<sup>th</sup> divisions of time:
<ul>
<li><em>1/7 (8th septuplet)</em>: shows one grid line per seventh bar</li>
<li><em>...</em></li>
<li><em>1/28 (32th septuplet)</em>: shows one grid line per 28<sup>th</sup> bar</li>
</ul>
</li>
</ul>
<p>
If items are moved on a track, and only the current track is selected, then
snapping will only happen with other regions on the same track. This means
that enabling <kbd class="menu">Edit &gt; Preferences &gt; Editor &gt; Link
Selections of Regions and Tracks</kbd> will make the "Region" grid unit
unusable. This option should not be used in conjunction with the use any of the
Region grid units.
Or absolute time:
</p>
<ul>
<li><em>Timecode</em>: shows one grid every <a href="@@on-clock-and-time">frame</a></li>
<li><em>MinSec</em>: shows one grid line every thousandth of a second</li>
<li><em>CD Frames</em>: shows one grid line per CD Frame (1/75<sup>th</sup> second)</li>
</ul>
<p class="warning">
The grid consist of lines running vertically in the edit canvas. When
zooming too far out, the grid can become too coarse. Ardour tries not
to show “too many” or “too few” grid lines depending on the zoom level,
based on the <em>Approximate Grid/Ruler granularity (pixels)</em> <a
href="@@preferences#preferences-editor-snap">Preferences</a> parameter.
As a consequence, when the Grid is in the Snap anchors, it is possible
that items snap in-between the grid lines sometimes. Thats expected
behavior.
</p>
<h3>Syncing Regions to the Grid</h2>
<p>
By default, a region's beginning will be used as the reference for
both types of snapping, this behaviour can be changed by setting a
<dfn>sync point</dfn> in the region, by selecting the region(s) and
pressing <kbd>V</kbd>. This will set the sync point to the current <a
href="@@edit-point-control">edit point</a>.
</p>
<h3>Keyboard modifiers</h3>
<p>
Snapping can be temporarily disabled by using a keyboard modifier while
editing, <kbd class="mod2n"></kbd> by default.
</p>
<p>
Snapping can also be temporarily set to relative, i.e. snapping will
occur relative to the current position of the dragged item. E.g. if
the Grid is in the Snap options, and the grid is set to
<em>Bars</em>, using this keyboard modifier while dragging will snap
at every bar relative to the region's beginning (or sync point)
instead of the absolute musical bars.
</p>
<p>
The keyboard modifiers are defined in the <a
href="@@preferences#preferences-editor-modifiers">Preferences</a>.
</p>