glfw/docs/window.dox

/*!

@page window Window handling guide
 
@tableofcontents

The primary purpose of GLFW is to provide a simple interface to window
management and OpenGL and OpenGL ES context creation.  GLFW supports multiple
windows, which can be either a normal desktop window or a full screen window.


@section window_object Window handles

The @ref GLFWwindow object encapsulates both a window and a context.  They are
created with @ref glfwCreateWindow and destroyed with @ref glfwDestroyWindow (or
@ref glfwTerminate, if any remain).  As the window and context are inseparably
linked, the object pointer is used as both a context and window handle.


@section window_creation Window creation

The window and its context are created with @ref glfwCreateWindow, which
returns a handle to the created window object.  For example, this creates a 640
by 480 windowed mode window:

@code
GLFWwindow* window = glfwCreateWindow(640, 480, "My Title", NULL, NULL);
if (!window)
{
    // Handle window creation failure
}
@endcode

If window creation fails, `NULL` will be returned, so you need to check the
return value.  If creation failed, an error will have been reported to the error
callback.

This handle is then passed to all window related functions, and is provided to
you along with input events, so you know which window received the input.

To create a full screen window, you need to specify which monitor the window
should use.  In most cases, the user's primary monitor is a good choice.  For
more information about monitors, see the @ref monitor.

@code
GLFWwindow* window = glfwCreateWindow(640, 480, "My Title", glfwGetPrimaryMonitor(), NULL);
@endcode

Full screen windows cover the entire display area of a monitor, have no border
or decorations, and change the monitor's resolution to the one most closely
matching the requested window size.

For more control over how the window and its context are created, see @ref
window_hints below.


@section window_destruction Window destruction

When you are done with the window, destroy it with the @ref glfwDestroyWindow
function.

@code
glfwDestroyWindow(window);
@endcode

Once this function is called, no more events will be delivered for that window
and its handle becomes invalid.


@section window_userptr Window user pointer

Each window has a user pointer that can be set with @ref
glfwSetWindowUserPointer and fetched with @ref glfwGetWindowUserPointer.  This
can be used for any purpose you need and will not be modified by GLFW throughout
the life-time of the window.


@section window_hints Window creation hints

There are a number of hints that can be set before the creation of a window and
context.  Some affect the window itself, others affect the framebuffer or
context.  These hints are set to their default values each time the library is
initialized with @ref glfwInit, can be set individually with @ref glfwWindowHint
and reset all at once to their defaults with @ref glfwDefaultWindowHints.

Note that hints need to be set *before* the creation of the window and context
you wish to have the specified attributes.


@subsection window_hints_hard Hard and soft constraints

Some window hints are hard constraints.  These must match the available
capabilities *exactly* for window and context creation to succeed.  Hints
that are not hard constraints are matched as closely as possible, but the
resulting window and context may differ from what these hints requested.  To
find out the actual attributes of the created window and context, use the
@ref glfwGetWindowAttrib function.

The following hints are always hard constraints:
- `GLFW_STEREO`
- `GLFW_DOUBLEBUFFER`
- `GLFW_CLIENT_API`

The following additional hints are hard constraints when requesting an OpenGL
context, but are ignored when requesting an OpenGL ES context:
- `GLFW_OPENGL_FORWARD_COMPAT`
- `GLFW_OPENGL_PROFILE`


@subsection window_hints_wnd Window related hints

The `GLFW_RESIZABLE` hint specifies whether the (windowed mode) window will be
resizable *by the user*.  The window will still be resizable using the @ref
glfwSetWindowSize function.  This hint is ignored for full screen windows.

The `GLFW_VISIBLE` hint specifies whether the (windowed mode) window will be
initially visible.  This hint is ignored for full screen windows.

The `GLFW_DECORATED` hint specifies whether the (windowed mode) window will have
window decorations such as a border, a close widget, etc.  This hint is ignored
for full screen windows.  Note that even though a window may lack a close
widget, it is usually still possible for the user to generate close events.

The `GLFW_FOCUSED` hint specifies whether the (windowed mode) window will be
given input focus when created.  This hint is ignored for full screen and
initially hidden windows.

The `GLFW_AUTO_ICONIFY` hint specifies whether the (full screen) window
will automatically iconify and restore the previous video mode on focus loss.
This hint is ignored for windowed mode windows.

The `GLFW_FLOATING` hint specifies whether the window will be floating above
other regular windows, also called topmost or always-on-top.  This is intended
primarily for debugging purposes and cannot be used to implement proper full
screen windows.  This hint is ignored for full screen windows.


@subsection window_hints_fb Framebuffer related hints

The `GLFW_RED_BITS`, `GLFW_GREEN_BITS`, `GLFW_BLUE_BITS`, `GLFW_ALPHA_BITS`,
`GLFW_DEPTH_BITS` and `GLFW_STENCIL_BITS` hints specify the desired bit
depths of the various components of the default framebuffer.  `GLFW_DONT_CARE`
means the application has no preference.

The `GLFW_ACCUM_RED_BITS`, `GLFW_ACCUM_GREEN_BITS`, `GLFW_ACCUM_BLUE_BITS`
and `GLFW_ACCUM_ALPHA_BITS` hints specify the desired bit depths of the
various components of the accumulation buffer.  `GLFW_DONT_CARE` means the
application has no preference.

@note Accumulation buffers are a legacy OpenGL feature and should not be used in
new code.

The `GLFW_AUX_BUFFERS` hint specifies the desired number of auxiliary
buffers.  `GLFW_DONT_CARE` means the application has no preference.

@note Auxiliary buffers are a legacy OpenGL feature and should not be used in
new code.

The `GLFW_STEREO` hint specifies whether to use stereoscopic rendering.  This is
a hard constraint.

The `GLFW_SAMPLES` hint specifies the desired number of samples to use for
multisampling.  Zero disables multisampling.  `GLFW_DONT_CARE` means the
application has no preference.

The `GLFW_SRGB_CAPABLE` hint specifies whether the framebuffer should be
sRGB capable.

The `GLFW_DOUBLEBUFFER` hint specifies whether the framebuffer should be double
buffered.  You nearly always want to use double buffering.  This is a hard
constraint.

The `GLFW_REFRESH_RATE` hint specifies the desired refresh rate for full screen
windows.  If set to zero, the highest available refresh rate will be used.  This
hint is ignored for windowed mode windows.


@subsection window_hints_ctx Context related hints

The `GLFW_CLIENT_API` hint specifies which client API to create the context
for.  Possible values are `GLFW_OPENGL_API` and `GLFW_OPENGL_ES_API`.  This is
a hard constraint.

The `GLFW_CONTEXT_VERSION_MAJOR` and `GLFW_CONTEXT_VERSION_MINOR` hints
specify the client API version that the created context must be compatible
with.

For OpenGL, these hints are *not* hard constraints, as they don't have to
match exactly, but @ref glfwCreateWindow will still fail if the resulting
OpenGL version is less than the one requested.  It is therefore perfectly
safe to use the default of version 1.0 for legacy code and you may still
get backwards-compatible contexts of version 3.0 and above when available.

While there is no way to ask the driver for a context of the highest supported
version, most drivers provide this when you ask GLFW for a version
1.0 context.

For OpenGL ES, these hints are hard constraints.

If an OpenGL context is requested, the `GLFW_OPENGL_FORWARD_COMPAT` hint
specifies whether the OpenGL context should be forward-compatible, i.e. one
where all functionality deprecated in the requested version of OpenGL is
removed.  This may only be used if the requested OpenGL version is 3.0 or
above.  If another client API is requested, this hint is ignored.

@note Forward-compatibility is described in detail in the
[OpenGL Reference Manual](https://www.opengl.org/registry/).

If an OpenGL context is requested, the `GLFW_OPENGL_DEBUG_CONTEXT` hint
specifies whether to create a debug OpenGL context, which may have
additional error and performance issue reporting functionality.  If another
client API is requested, this hint is ignored.

If an OpenGL context is requested, the `GLFW_OPENGL_PROFILE` hint specifies
which OpenGL profile to create the context for.  Possible values are one of
`GLFW_OPENGL_CORE_PROFILE` or `GLFW_OPENGL_COMPAT_PROFILE`, or
`GLFW_OPENGL_ANY_PROFILE` to not request a specific profile.  If requesting
an OpenGL version below 3.2, `GLFW_OPENGL_ANY_PROFILE` must be used.  If
another client API is requested, this hint is ignored.

@note OpenGL profiles are described in detail in the
[OpenGL Reference Manual](https://www.opengl.org/registry/).

The `GLFW_CONTEXT_ROBUSTNESS` hint specifies the robustness strategy to be
used by the context.  This can be one of `GLFW_NO_RESET_NOTIFICATION` or
`GLFW_LOSE_CONTEXT_ON_RESET`, or `GLFW_NO_ROBUSTNESS` to not request
a robustness strategy.

The `GLFW_CONTEXT_RELEASE_BEHAVIOR` hint specifies the release behavior to be
used by the context.  Possible values are one of `GLFW_ANY_RELEASE_BEHAVIOR`,
`GLFW_RELEASE_BEHAVIOR_FLUSH` or `GLFW_RELEASE_BEHAVIOR_NONE`.  If the
behavior is `GLFW_ANY_RELEASE_BEHAVIOR`, the default behavior of the context
creation API will be used.  If the behavior is `GLFW_RELEASE_BEHAVIOR_FLUSH`,
the pipeline will be flushed whenever the context is released from being the
current one.  If the behavior is `GLFW_RELEASE_BEHAVIOR_NONE`, the pipeline will
not be flushed on release.

@note Context release behaviors are described in detail by the
[GL_KHR_context_flush_control](https://www.opengl.org/registry/specs/KHR/context_flush_control.txt)
extension.


@subsection window_hints_values Supported and default values

| Name                            | Default value               | Supported values        |
| ------------------------------- | --------------------------- | ----------------------- |
| `GLFW_RESIZABLE`                | `GL_TRUE`                   | `GL_TRUE` or `GL_FALSE` |
| `GLFW_VISIBLE`                  | `GL_TRUE`                   | `GL_TRUE` or `GL_FALSE` |
| `GLFW_DECORATED`                | `GL_TRUE`                   | `GL_TRUE` or `GL_FALSE` |
| `GLFW_FOCUSED`                  | `GL_TRUE`                   | `GL_TRUE` or `GL_FALSE` |
| `GLFW_AUTO_ICONIFY`             | `GL_TRUE`                   | `GL_TRUE` or `GL_FALSE` |
| `GLFW_FLOATING`                 | `GL_FALSE`                  | `GL_TRUE` or `GL_FALSE` |
| `GLFW_RED_BITS`                 | 8                           | 0 to `INT_MAX` or `GLFW_DONT_CARE` |
| `GLFW_GREEN_BITS`               | 8                           | 0 to `INT_MAX` or `GLFW_DONT_CARE` |
| `GLFW_BLUE_BITS`                | 8                           | 0 to `INT_MAX` or `GLFW_DONT_CARE` |
| `GLFW_ALPHA_BITS`               | 8                           | 0 to `INT_MAX` or `GLFW_DONT_CARE` |
| `GLFW_DEPTH_BITS`               | 24                          | 0 to `INT_MAX` or `GLFW_DONT_CARE` |
| `GLFW_STENCIL_BITS`             | 8                           | 0 to `INT_MAX` or `GLFW_DONT_CARE` |
| `GLFW_ACCUM_RED_BITS`           | 0                           | 0 to `INT_MAX` or `GLFW_DONT_CARE` |
| `GLFW_ACCUM_GREEN_BITS`         | 0                           | 0 to `INT_MAX` or `GLFW_DONT_CARE` |
| `GLFW_ACCUM_BLUE_BITS`          | 0                           | 0 to `INT_MAX` or `GLFW_DONT_CARE` |
| `GLFW_ACCUM_ALPHA_BITS`         | 0                           | 0 to `INT_MAX` or `GLFW_DONT_CARE` |
| `GLFW_AUX_BUFFERS`              | 0                           | 0 to `INT_MAX` or `GLFW_DONT_CARE` |
| `GLFW_SAMPLES`                  | 0                           | 0 to `INT_MAX` or `GLFW_DONT_CARE` |
| `GLFW_REFRESH_RATE`             | 0                           | 0 to `INT_MAX` or `GLFW_DONT_CARE` |
| `GLFW_STEREO`                   | `GL_FALSE`                  | `GL_TRUE` or `GL_FALSE` |
| `GLFW_SRGB_CAPABLE`             | `GL_FALSE`                  | `GL_TRUE` or `GL_FALSE` |
| `GLFW_DOUBLEBUFFER`             | `GL_TRUE`                   | `GL_TRUE` or `GL_FALSE` |
| `GLFW_CLIENT_API`               | `GLFW_OPENGL_API`           | `GLFW_OPENGL_API` or `GLFW_OPENGL_ES_API` |
| `GLFW_CONTEXT_VERSION_MAJOR`    | 1                           | Any valid major version number of the chosen client API |
| `GLFW_CONTEXT_VERSION_MINOR`    | 0                           | Any valid minor version number of the chosen client API |
| `GLFW_CONTEXT_ROBUSTNESS`       | `GLFW_NO_ROBUSTNESS`        | `GLFW_NO_ROBUSTNESS`, `GLFW_NO_RESET_NOTIFICATION` or `GLFW_LOSE_CONTEXT_ON_RESET` |
| `GLFW_CONTEXT_RELEASE_BEHAVIOR` | `GLFW_ANY_RELEASE_BEHAVIOR` | `GLFW_ANY_RELEASE_BEHAVIOR`, `GLFW_RELEASE_BEHAVIOR_FLUSH` or `GLFW_RELEASE_BEHAVIOR_NONE` |
| `GLFW_OPENGL_FORWARD_COMPAT`    | `GL_FALSE`                  | `GL_TRUE` or `GL_FALSE` |
| `GLFW_OPENGL_DEBUG_CONTEXT`     | `GL_FALSE`                  | `GL_TRUE` or `GL_FALSE` |
| `GLFW_OPENGL_PROFILE`           | `GLFW_OPENGL_ANY_PROFILE`   | `GLFW_OPENGL_ANY_PROFILE`, `GLFW_OPENGL_COMPAT_PROFILE` or `GLFW_OPENGL_CORE_PROFILE` |


@section window_close Window close flag

When the user attempts to close the window, for example by clicking the close
widget or using a key chord like Alt+F4, the *close flag* of the window is set.
The window is however not actually destroyed and, unless you watch for this
state change, nothing further happens.

The current state of the close flag is returned by @ref glfwWindowShouldClose
and can be set or cleared directly with @ref glfwSetWindowShouldClose.  A common
pattern is to use the close flag as a main loop condition.

@code
while (!glfwWindowShouldClose(window))
{
    render(window);

    glfwSwapBuffers(window);
    glfwPollEvents();
}
@endcode

If you wish to be notified when the user attempts to close a window, you can set
the close callback with @ref glfwSetWindowCloseCallback.  This callback is
called directly *after* the close flag has been set.

@code
glfwSetWindowCloseCallback(window, window_close_callback);
@endcode

The callback function can be used for example to filter close requests and clear
the close flag again unless certain conditions are met.

@code
void window_close_callback(GLFWwindow* window)
{
    if (!time_to_close)
        glfwSetWindowShouldClose(window, GL_FALSE);
}
@endcode


@section window_size Window size

The size of a window can be changed with @ref glfwSetWindowSize.  For windowed
mode windows, this resizes the specified window so that its *client area* has
the specified size.  Note that the window system may put limitations on size.
For full screen windows, it selects and sets the video mode most closely
matching the specified size.

@code
void glfwSetWindowSize(window, 640, 480);
@endcode

If you wish to be notified when a window is resized, whether by the user or
the system, you can set the size callback with @ref glfwSetWindowSizeCallback.

@code
glfwSetWindowSizeCallback(window, window_size_callback);
@endcode

The callback function receives the new size of the client area of the window.

@code
void window_size_callback(GLFWwindow* window, int width, int height)
{
}
@endcode

There is also @ref glfwGetWindowSize for directly retrieving the current size of
a window.

@code
int width, height;
glfwGetWindowSize(window, &width, &height);
@endcode

@note Do not pass the window size to `glViewport` or other pixel-based OpenGL
calls.  The window size is in screen coordinates, not pixels.  Use the
framebuffer size, which is in pixels, for pixel-based calls.


@section window_fbsize Window framebuffer size

While the size of a window is measured in screen coordinates, OpenGL works with
pixels.  The size you pass into `glViewport`, for example, should be in pixels
and not screen coordinates.  On some platforms screen coordinates and pixels are
the same, but this is not the case on all platforms supported by GLFW.  There is
a second set of functions to retrieve the size in pixels of the framebuffer of
a window.

If you wish to be notified when the framebuffer of a window is resized, whether
by the user or the system, you can set the size callback with @ref
glfwSetFramebufferSizeCallback.

@code
glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);
@endcode

The callback function receives the new size of the client area of the window,
which can for example be used to update the OpenGL viewport.

@code
void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
    glViewport(0, 0, width, height);
}
@endcode

There is also @ref glfwGetFramebufferSize for directly retrieving the current
size of the framebuffer of a window.

@code
int width, height;
glfwGetFramebufferSize(window, &width, &height);
glViewport(0, 0, width, height);
@endcode

Note that the size of a framebuffer may change independently of the size of
a window, for example if the window is dragged between a regular monitor and
a high-DPI one.


@section window_pos Window position

The position of a windowed-mode window can be changed with @ref
glfwSetWindowPos.  This moves the window so that the upper-left corner of its
client area has the specified screen coordinates.  Note that the window system
may put limitations on placement.

@code
glfwSetWindowPos(window, 100, 100);
@endcode

If you wish to be notified when a window is moved, whether by the user or
the system, you can set the position callback with @ref glfwSetWindowPosCallback.

@code
glfwSetWindowPosCallback(window, window_pos_callback);
@endcode

The callback function receives the new position of the upper-left corner of its
client area.

@code
void window_pos_callback(GLFWwindow* window, int xpos, int ypos)
{
}
@endcode

There is also @ref glfwGetWindowPos for directly retrieving the current position
of the client area of the window.

@code
int xpos, ypos;
glfwGetWindowPos(window, &xpos, &ypos);
@endcode


@section window_title Window title

All GLFW windows have a title, although undecorated or full screen windows may
not display it or only display it in a task bar or similar interface.  To change
the title of a window, use @ref glfwSetWindowTitle.

@code
glfwSetWindowTitle(window, "My Window");
@endcode

The window title is a regular C string using the UTF-8 encoding.  This means
for example that, as long as your source file is encoded as UTF-8, you can use
any Unicode characters.

@code
glfwSetWindowTitle(window, "さよなら絶望先生");
@endcode


@section window_attribs Window attributes

Windows have a number of attributes that can be returned using @ref
glfwGetWindowAttrib.  Some reflect state that may change during the lifetime of
the window, while others reflect the corresponding hints and are fixed at the
time of creation.

@code
if (glfwGetWindowAttrib(window, GLFW_FOCUSED))
{
    // window has input focus
}
@endcode


@subsection window_attribs_window Window attributes

The `GLFW_FOCUSED` attribute indicates whether the specified window currently
has input focus.

The `GLFW_ICONIFIED` attribute indicates whether the specified window is
currently iconified, whether by the user or with @ref glfwIconifyWindow.

The `GLFW_VISIBLE` attribute indicates whether the specified window is currently
visible.  Window visibility can be controlled with @ref glfwShowWindow and @ref
glfwHideWindow and initial visibility is controlled by the
[window hint](@ref window_hints) with the same name.  

The `GLFW_RESIZABLE` attribute indicates whether the specified window is
resizable *by the user*.  This is controlled by the
[window hint](@ref window_hints) with the same name.

The `GLFW_DECORATED` attribute indicates whether the specified window has
decorations such as a border, a close widget, etc.  This is controlled by the
[window hint](@ref window_hints) with the same name. 

The `GLFW_FLOATING` attribute indicates whether the specified window is
floating, also called topmost or always-on-top.  This is controlled by the
[window hint](@ref window_hints) with the same name. 


@subsection window_attribs_context Context attributes

The `GLFW_CLIENT_API` attribute indicates the client API provided by the
window's context; either `GLFW_OPENGL_API` or `GLFW_OPENGL_ES_API`.

The `GLFW_CONTEXT_VERSION_MAJOR`, `GLFW_CONTEXT_VERSION_MINOR` and
`GLFW_CONTEXT_REVISION` attributes indicate the client API version of the
window's context.

The `GLFW_OPENGL_FORWARD_COMPAT` attribute is `GL_TRUE` if the window's
context is an OpenGL forward-compatible one, or `GL_FALSE` otherwise.

The `GLFW_OPENGL_DEBUG_CONTEXT` attribute is `GL_TRUE` if the window's
context is an OpenGL debug context, or `GL_FALSE` otherwise.

The `GLFW_OPENGL_PROFILE` attribute indicates the OpenGL profile used by the
context.  This is `GLFW_OPENGL_CORE_PROFILE` or `GLFW_OPENGL_COMPAT_PROFILE`
if the context uses a known profile, or `GLFW_OPENGL_ANY_PROFILE` if the
OpenGL profile is unknown or the context is for another client API.  Note that
the returned profile may not match the profile bits of the context flags, as
GLFW will try other means of detecting the profile when no bits are set.

The `GLFW_CONTEXT_ROBUSTNESS` attribute indicates the robustness strategy
used by the context.  This is `GLFW_LOSE_CONTEXT_ON_RESET` or
`GLFW_NO_RESET_NOTIFICATION` if the window's context supports robustness, or
`GLFW_NO_ROBUSTNESS` otherwise.


@section window_swap Swapping buffers

GLFW windows are by default double buffered.  That means that you have two
rendering buffers; a front buffer and a back buffer.  The front buffer is
the one being displayed and the back buffer the one you render to.

When the entire frame has been rendered, it is time to swap the back and the
front buffers in order to display what has been rendered and begin rendering
a new frame.  This is done with @ref glfwSwapBuffers.

@code
glfwSwapBuffers(window);
@endcode

Sometimes it can be useful to select when the buffer swap will occur.  With the
function @ref glfwSwapInterval it is possible to select the minimum number of
monitor refreshes the driver should wait before swapping the buffers:

@code
glfwSwapInterval(1);
@endcode

If the interval is zero, the swap will take place immediately when @ref
glfwSwapBuffers is called without waiting for a refresh.  Otherwise at least
interval retraces will pass between each buffer swap.  Using a swap interval of
zero can be useful for benchmarking purposes, when it is not desirable to
measure the time it takes to wait for the vertical retrace.  However, a swap
interval of one lets you avoid tearing.

Note that this may not work on all machines, as some drivers have
user-controlled settings that override any swap interval the application
requests.  It is also by default disabled on Windows Vista and later when using
DWM (Aero), as using it there sometimes leads to severe jitter.  You can
forcibly enable it for machines using DWM using @ref compile_options_win32.

*/