Windowing
=========

A :py:class:`~pyglet.window.Window` in pyglet corresponds to a top-level
window provided by the operating system.  Windows can be floating
(overlapped with other application windows) or fullscreen.

.. _guide_creating-a-window:

Creating a window
-----------------

If the :py:class:`~pyglet.window.Window` constructor is called with no
arguments, defaults will be assumed for all parameters::

    window = pyglet.window.Window()

The default parameters used are:

* The window will have a size of 960x540, and not be resizable.
* A default context will be created using template config described in
  :ref:`guide_glconfig`.
* The window caption will be the name of the executing Python script
  (i.e., ``sys.argv[0]``).

Windows are visible as soon as they are created, unless you give the
``visible=False`` argument to the constructor.  The following
example shows how to create and display a window in two steps::

    window = pyglet.window.Window(visible=False)
    # ... perform some additional initialisation
    window.set_visible()

OpenGL Context configuration
^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The context of a window cannot be changed once created.  There are several
ways to control the context that is created:

* Supply an already-created :py:class:`~pyglet.gl.Context` using the
  ``context`` argument::

      context = config.create_context(share)
      window = pyglet.window.Window(context=context)

* Supply a complete :py:class:`~pyglet.gl.Config` obtained from a
  :py:class:`~pyglet.canvas.Screen` using the ``config``
  argument.  The context will be created from this config and will share object
  space with the most recently created existing context::

      config = screen.get_best_config(template)
      window = pyglet.window.Window(config=config)

* Supply a template :py:class:`~pyglet.gl.Config` using the ``config``
  argument. The context will use the best config obtained from the default
  screen of the default display::

      config = gl.Config(double_buffer=True)
      window = pyglet.window.Window(config=config)

* Specify a :py:class:`~pyglet.canvas.Screen` using the ``screen`` argument.
  The context will use a config created from default template configuration
  and this screen::

      screen = display.get_screens()[screen_number]
      window = pyglet.window.Window(screen=screen)

* Specify a :py:class:`~pyglet.canvas.Display` using the ``display`` argument.
  The default screen on this display will be used to obtain a context using
  the default template configuration::

      display = platform.get_display(display_name)
      window = pyglet.window.Window(display=display)

If a template :py:class:`~pyglet.gl.Config` is given, a
:py:class:`~pyglet.canvas.Screen` or :py:class:`~pyglet.canvas.Display`
may also be specified; however any other combination of parameters
overconstrains the configuration and some parameters will be ignored.

Fullscreen windows
^^^^^^^^^^^^^^^^^^

If the ``fullscreen=True`` argument is given to the window constructor, the
window will draw to an entire screen rather than a floating window.  No window
border or controls will be shown, so you must ensure you provide some other
means to exit the application.

By default, the default screen on the default display will be used, however
you can optionally specify another screen to use instead.  For example, the
following code creates a fullscreen window on the secondary screen::

    screens = display.get_screens()
    window = pyglet.window.Window(fullscreen=True, screen=screens[1])

There is no way to create a fullscreen window that spans more than one window
(for example, if you wanted to create an immersive 3D environment across
multiple monitors).  Instead, you should create a separate fullscreen window
for each screen and attach identical event handlers to all windows.

Windows can be toggled in and out of fullscreen mode with the
:py:meth:`~pyglet.window.Window.set_fullscreen`
method.  For example, to return to windowed mode from fullscreen::

    window.set_fullscreen(False)

The previous window size and location, if any, will attempt to be restored,
however the operating system does not always permit this, and the window may
have relocated.

Size and position
-----------------

This section applies only to windows that are not fullscreen.  Fullscreen
windows always have the width and height of the screen they fill.

You can specify the size of a window as the first two arguments to the window
constructor.  In the following example, a window is created with a width of
1280 pixels and a height of 720 pixels::

    window = pyglet.window.Window(1280, 720)

The "size" of a window refers to the drawable space within it, excluding any
additional borders or title bar drawn by the operating system.

You can allow the user to resize your window by specifying ``resizable=True``
in the constructor.  If you do this, you may also want to handle the
:py:meth:`~pyglet.window.Window.on_resize` event::

    window = pyglet.window.Window(resizable=True)

    @window.event
    def on_resize(width, height):
        print(f'The window was resized to {width},{height}')

You can specify a minimum and maximum size that the window can be resized to
by the user with the :py:meth:`~pyglet.window.Window.set_minimum_size` and
:py:meth:`~pyglet.window.Window.set_maximum_size` methods::

    window.set_minimum_size(320, 200)
    window.set_maximum_size(1024, 768)

The window can also be resized programatically (even if the window is not
user-resizable) with the :py:meth:`~pyglet.window.Window.set_size` method::

    window.set_size(1280, 720)

The window will initially be positioned by the operating system.  Typically,
it will use its own algorithm to locate the window in a place that does not
block other application windows, or cascades with them.  You can manually
adjust the position of the window using the
:py:meth:`~pyglet.window.Window.get_location` and
:py:meth:`~pyglet.window.Window.set_location` methods::

    x, y = window.get_location()
    window.set_location(x + 20, y + 20)

Note that unlike the usual coordinate system in pyglet, the window location is
relative to the top-left corner of the desktop, as shown in the following
diagram:

.. figure:: img/window_location.png

    The position and size of the window relative to the desktop.

Appearance
----------

Window style
^^^^^^^^^^^^

Non-fullscreen windows can be created in one of four styles: default, dialog,
tool or borderless.  Examples of the appearances of each of these styles under
Windows and Mac OS X 10.4 are shown below.

    .. list-table::
        :header-rows: 1

        * - Style
          - Windows
          - Mac OS X
        * - :py:attr:`~pyglet.window.Window.WINDOW_STYLE_DEFAULT`
          - .. image:: img/window_xp_default.png
          - .. image:: img/window_osx_default.png
        * - :py:attr:`~pyglet.window.Window.WINDOW_STYLE_DIALOG`
          - .. image:: img/window_xp_dialog.png
          - .. image:: img/window_osx_dialog.png
        * - :py:attr:`~pyglet.window.Window.WINDOW_STYLE_TOOL`
          - .. image:: img/window_xp_tool.png
          - .. image:: img/window_osx_tool.png
        * - :py:attr:`~pyglet.window.Window.WINDOW_STYLE_TRANSPARENT`
          - .. image:: img/window_xp_transparent.png
          - <Not Implemented>
        * - :py:attr:`~pyglet.window.Window.WINDOW_STYLE_OVERLAY`
          - .. image:: img/window_xp_overlay.png
          - <Not Implemented>

Non-resizable variants of these window styles may appear slightly different
(for example, the maximize button will either be disabled or absent).

Besides the change in appearance, the window styles affect how the window
behaves.  For example, tool windows do not usually appear in the task bar and
cannot receive keyboard focus.  Dialog windows cannot be minimized. Overlay's
require custom sizing and moving of the respective window.
the appropriate window style for your windows means your application will
behave correctly for the platform on which it is running, however that
behaviour may not be consistent across Windows, Linux and Mac OS X.

The appearance and behaviour of windows in Linux will vary greatly depending
on the distribution, window manager and user preferences.

Borderless windows (:py:attr:`~pyglet.window.Window.WINDOW_STYLE_BORDERLESS`)
are not decorated by the operating system at all, and have no way to be resized
or moved around the desktop.  These are useful for implementing splash screens
or custom window borders.

You can specify the style of the window in the
:py:class:`~pyglet.window.Window` constructor.
Once created, the window style cannot be altered::

    window = pyglet.window.Window(style=pyglet.window.Window.WINDOW_STYLE_DIALOG)

Caption
^^^^^^^

The window's caption appears in its title bar and task bar icon (on Windows
and some Linux window managers).  You can set the caption during window
creation or at any later time using the
:py:meth:`~pyglet.window.Window.set_caption` method::

    window = pyglet.window.Window(caption='Initial caption')
    window.set_caption('A different caption')

Icon
^^^^

The window icon appears in the title bar and task bar icon on Windows and
Linux, and in the dock icon on Mac OS X.  Dialog and tool windows do not
necessarily show their icon.

Windows, Mac OS X and the Linux window managers each have their own preferred
icon sizes:

    Windows XP
        * A 16x16 icon for the title bar and task bar.
        * A 32x32 icon for the Alt+Tab switcher.
    Mac OS X
        * Any number of icons of resolutions 16x16, 24x24, 32x32, 48x48, 72x72
          and 128x128.  The actual image displayed will be interpolated to the
          correct size from those provided.
    Linux
        * No constraints, however most window managers will use a 16x16 and a
          32x32 icon in the same way as Windows XP.

The :py:meth:`~pyglet.window.Window.set_icon` method allows you to set any
number of images as the icon.
pyglet will select the most appropriate ones to use and apply them to
the window.  If an alternate size is required but not provided, pyglet will
scale the image to the correct size using a simple interpolation algorithm.

The following example provides both a 16x16 and a 32x32 image as the window
icon::

    window = pyglet.window.Window()
    icon1 = pyglet.image.load('16x16.png')
    icon2 = pyglet.image.load('32x32.png')
    window.set_icon(icon1, icon2)

You can use images in any format supported by pyglet, however it is
recommended to use a format that supports alpha transparency such as PNG.
Windows .ico files are supported only on Windows, so their use is discouraged.
Mac OS X .icons files are not supported at all.

Note that the icon that you set at runtime need not have anything to do with
the application icon, which must be encoded specially in the application
binary (see `Self-contained executables`).

Visibility
----------

Windows have several states of visibility.  Already shown is the
:py:attr:`~pyglet.window.Window.visible` property which shows or hides
the window.

Windows can be minimized, which is equivalent to hiding them except that
they still appear on the taskbar (or are minimised to the dock, on OS X).
The user can minimize a window by clicking the appropriate button in the
title bar.
You can also programmatically minimize a window using the
:py:class:`~pyglet.window.Window.minimize` method (there is also a
corresponding :py:class:`~pyglet.window.Window.maximize` method).

When a window is made visible the :py:meth:`~pyglet.window.Window.on_show`
event is triggered.  When it is hidden the
:py:meth:`~pyglet.window.Window.on_hide` event is triggered.
On Windows and Linux these events
will only occur when you manually change the visibility of the window or when
the window is minimized or restored.  On Mac OS X the user can also hide or
show the window (affecting visibility) using the Command+H shortcut.

.. _guide_subclassing-window:

Subclassing Window
------------------

A useful pattern in pyglet is to subclass :py:class:`~pyglet.window.Window` for
each type of window you will display, or as your main application class.  There
are several benefits:

* You can load font and other resources from the constructor, ensuring the
  OpenGL context has already been created.
* You can add event handlers simply by defining them on the class.  The
  :py:meth:`~pyglet.window.Window.on_resize` event will be called as soon as
  the window is created (this
  doesn't usually happen, as you must create the window before you can attach
  event handlers).
* There is reduced need for global variables, as you can maintain application
  state on the window.

The following example shows the same "Hello World" application as presented
in :ref:`quickstart`, using a subclass of :py:class:`~pyglet.window.Window`::

    class HelloWorldWindow(pyglet.window.Window):
        def __init__(self):
            super().__init__()

            self.label = pyglet.text.Label('Hello, world!')

        def on_draw(self):
            self.clear()
            self.label.draw()

    if __name__ == '__main__':
        window = HelloWorldWindow()
        pyglet.app.run()

This example program is located in
``examples/programming_guide/window_subclass.py``.

Windows and OpenGL contexts
---------------------------

Every window in pyglet has an associated OpenGL context.
Specifying the configuration of this context has already been covered in
:ref:`guide_creating-a-window`.
Drawing into the OpenGL context is the only way to draw into the window's
client area.

Double-buffering
^^^^^^^^^^^^^^^^

If the window is double-buffered (i.e., the configuration specified
``double_buffer=True``, the default), OpenGL commands are applied to a hidden
back buffer. This back buffer can be brought to the front using the `flip`
method. The previous front buffer then becomes the hidden back buffer
we render to in the next frame. If you are using the standard `pyglet.app.run`
or :py:class:`pyglet.app.EventLoop` event loop, this is taken care of
automatically after each :py:meth:`~pyglet.window.Window.on_draw` event.

If the window is not double-buffered, the
:py:meth:`~pyglet.window.Window.flip`  operation is unnecessary,
and you should remember only to call :py:func:`pyglet.gl.glFlush` to
ensure buffered commands are executed.

Vertical retrace synchronisation
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Double-buffering eliminates one cause of flickering: the user is unable to see
the image as it is painted, only the final rendering.  However, it does introduce
another source of flicker known as "tearing".

Tearing becomes apparent when displaying fast-moving objects in an animation.
The buffer flip occurs while the video display is still reading data from the
framebuffer, causing the top half of the display to show the previous frame
while the bottom half shows the updated frame.  If you are updating the
framebuffer particularly quickly you may notice three or more such "tears" in
the display.

pyglet provides a way to avoid tearing by synchronising buffer flips to the
video refresh rate.  This is enabled by default, but can be set or unset
manually at any time with the :py:attr:`~pyglet.window.Window.vsync` (vertical
retrace synchronisation)
property.  A window is created with vsync initially disabled in the following
example::

    window = pyglet.window.Window(vsync=False)

It is usually desirable to leave vsync enabled, as it results in flicker-free
animation.  There are some use-cases where you may want to disable it, for
example:

* Profiling an application.  Measuring the time taken to perform an operation
  will be affected by the time spent waiting for the video device to refresh,
  which can throw off results.  You should disable vsync if you are measuring
  the performance of your application.
* If you cannot afford for your application to block.  If your application run
  loop needs to quickly poll a hardware device, for example, you may want to
  avoid blocking with vsync.
