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/*!
\page qtquick-positioning-topic.html
\title Important Concepts In Qt Quick - Positioning
\brief Overview of positioning concepts

Visual items in QML can be positioned in a variety of ways.  The most important
positioning-related concept is that of anchoring, a form of relative
positioning where items can be anchored (or attached) to each other at certain
boundaries.  Other positioning concepts include absolute positioning,
positioning with coordinate bindings, and layouts.


\section1 Manual Positioning

Items can be positioned manually.  If the user-interface is going to be
static, manual positioning provides the most efficient form of positioning.

In any user-interface, the visual elements exist at a particular location in
the screen coordinates at any instant in time.  While fluidly animated and
dynamic user-interfaces are a major focus of Qt Quick, statically-positioned
user interfaces are still a viable option.  What's more, if the position of
those elements does not change, it can often be more performant to specify
the position manually than to use the more dynamic positioning methods
documented in proceeding sections.

In Qt Quick, every visual object is positioned within the
\l{qtquick-visual-coordinates.html}{coordinate system}
provided by the Qt Quick visual canvas.  As described in that document, the
x and y coordinates of a visual object are relative to those of its visual
parent, with the top-left corner having the coordinate (0, 0).

Thus, the following example will display two rectangles positioned manually:

\table
    \header
    \li Example Code
    \li Resultant Layout

    \row
    \li
        \qml
        import QtQuick 2.0

        Item {
            width: 200
            height: 200

            Rectangle {
                x: 50
                y: 50
                width: 100
                height: 100
                color: "green"
             }

             Rectangle {
                x: 100
                y: 100
                width: 50
                height: 50
                color: "yellow"
             }
        }
        \endqml
    \li
        \image manual-layout.png
\endtable

\section1 Positioning With Bindings

Items may also be positioned by assigning binding expressions to the properties
associated with their location in the visual canvas.  This type of positioning
is the most highly dynamic, however some performance cost is associated with
positioning items in this manner.

The position and dimensions of a visual object can also be set through property
bindings.  This has the advantage that the values will automatically be updated
as the dependencies of the bindings change.  For example, the width of one
Rectangle might depend on the width of the Rectangle next to it.

While bindings provide a very flexible and intuitive way of creating dynamic
layouts, it should be noted that there is some performance cost associated with
them, and where possible, pristine Anchor layouts should be preferred.


\section1 Anchors

Anchors allows an item to be placed either adjacent to or inside of another,
by attaching one or more of the item's anchor-points (boundaries) to an
anchor-point of the other.  These anchors will remain even if the dimensions
or location of one of the items changes, allowing for highly dynamic
user-interfaces.

A visual object can be thought of as having various anchor-points (or more
correctly, anchor-lines).  Other items can be anchored to those points, which
means that as any object changes, the other objects which are anchored to it
will adjust automatically to maintain the anchoring.

Qt Quick provides anchors as a top-level concept.  See the documentation about
\l{qtquick-positioning-anchors.html}{positioning with anchors}
for in-depth information on the topic.

It is important to note that anchor-based layouts are generally far more
performant than binding-based layouts, if pristine.  A "pristine" anchor layout
is one which uses only anchors (with object nesting) to determine the
positioning, whereas a "contaminated" anchor layout is one which uses both
anchoring and bindings (either on position-related [x,y] properties or on
dimension-related [width,height] properties) to determine the position.

\section1 Layouts

Qt Quick also provides some built-in layout items.  For many use cases, the
best layout to use is a simple grid, row, or column, and Qt Quick provides
items which will layout children in these formations in the most efficient
manner possible.

There are many well-known layouts which work well in user-interfaces, such as
grids and lists, rows and columns.  Qt Quick supports these sort of pre-defined
layouts, which can often be more performant to draw than anchor or
binding-based layouts.  See the documentation on
\l{qtquick-positioning-layouts.html}{layout elements} for more
information about utilizing pre-defined layouts.



\section1 Right-To-Left Support

The directionality of the written form of a language often has a great impact
on how the visual elements of a user-interface should be positioned.  Qt Quick
supports right-to-left positioning of elements through the predefined-layouts
as well as right-to-left text layouts.

Please see the documentation about
\l{qtquick-positioning-righttoleft.html}
{right-to-left support in Qt Quick} for in-depth information on the topic.


*/

