QOpenGLContext¶
The
QOpenGLContext
class represents a native OpenGL context, enabling OpenGL rendering on aQSurface
. More…
Synopsis¶
Functions¶
def
create
()def
defaultFramebufferObject
()def
doneCurrent
()def
extensions
()def
extraFunctions
()def
format
()def
functions
()def
hasExtension
(extension)def
isOpenGLES
()def
isValid
()def
makeCurrent
(surface)def
nativeHandle
()def
screen
()def
setFormat
(format)def
setNativeHandle
(handle)def
setScreen
(screen)def
setShareContext
(shareContext)def
shareContext
()def
shareGroup
()def
surface
()def
swapBuffers
(surface)def
versionFunctions
([versionProfile=QOpenGLVersionProfile()])
Signals¶
def
aboutToBeDestroyed
()
Static functions¶
def
areSharing
(first, second)def
currentContext
()def
globalShareContext
()def
openGLModuleHandle
()def
openGLModuleType
()def
supportsThreadedOpenGL
()
Detailed Description¶
QOpenGLContext
represents the OpenGL state of an underlying OpenGL context. To set up a context, set its screen and format such that they match those of the surface or surfaces with which the context is meant to be used, if necessary make it share resources with other contexts withsetShareContext()
, and finally callcreate()
. Use the return value orisValid()
to check if the context was successfully initialized.A context can be made current against a given surface by calling
makeCurrent()
. When OpenGL rendering is done, callswapBuffers()
to swap the front and back buffers of the surface, so that the newly rendered content becomes visible. To be able to support certain platforms,QOpenGLContext
requires that you callmakeCurrent()
again before starting rendering a new frame, after callingswapBuffers()
.If the context is temporarily not needed, such as when the application is not rendering, it can be useful to delete it in order to free resources. You can connect to the
aboutToBeDestroyed()
signal to clean up any resources that have been allocated with different ownership from theQOpenGLContext
itself.Once a
QOpenGLContext
has been made current, you can render to it in a platform independent way by using Qt’s OpenGL enablers such asQOpenGLFunctions
,QOpenGLBuffer
,QOpenGLShaderProgram
, andQOpenGLFramebufferObject
. It is also possible to use the platform’s OpenGL API directly, without using the Qt enablers, although potentially at the cost of portability. The latter is necessary when wanting to use OpenGL 1.x or OpenGL ES 1.x.For more information about the OpenGL API, refer to the official OpenGL documentation .
For an example of how to use
QOpenGLContext
see the OpenGL Window example.
Thread Affinity¶
QOpenGLContext
can be moved to a different thread withmoveToThread()
. Do not callmakeCurrent()
from a different thread than the one to which theQOpenGLContext
object belongs. A context can only be current in one thread and against one surface at a time, and a thread only has one context current at a time.
Context Resource Sharing¶
Resources such as textures and vertex buffer objects can be shared between contexts. Use
setShareContext()
before callingcreate()
to specify that the contexts should share these resources.QOpenGLContext
internally keeps track of aQOpenGLContextGroup
object which can be accessed withshareGroup()
, and which can be used to find all the contexts in a given share group. A share group consists of all contexts that have been successfully initialized and are sharing with an existing context in the share group. A non-sharing context has a share group consisting of a single context.
Default Framebuffer¶
On certain platforms, a framebuffer other than 0 might be the default frame buffer depending on the current surface. Instead of calling glBindFramebuffer(0), it is recommended that you use glBindFramebuffer(ctx->
defaultFramebufferObject()
), to ensure that your application is portable between different platforms. However, if you useglBindFramebuffer()
, this is done automatically for you.
- class PySide2.QtGui.QOpenGLContext([parent=None])¶
- param parent:
Creates a new OpenGL context instance with parent object
parent
.Before it can be used you need to set the proper format and call
create()
.See also
- PySide2.QtGui.QOpenGLContext.OpenGLModuleType¶
This enum defines the type of the underlying OpenGL implementation.
Constant
Description
QOpenGLContext.LibGL
OpenGL
QOpenGLContext.LibGLES
OpenGL ES 2.0 or higher
- PySide2.QtGui.QOpenGLContext.aboutToBeDestroyed()¶
- static PySide2.QtGui.QOpenGLContext.areSharing(first, second)¶
- Parameters:
first –
PySide2.QtGui.QOpenGLContext
second –
PySide2.QtGui.QOpenGLContext
- Return type:
bool
Returns
true
if thefirst
andsecond
contexts are sharing OpenGL resources.
- PySide2.QtGui.QOpenGLContext.create()¶
- Return type:
bool
Attempts to create the OpenGL context with the current configuration.
The current configuration includes the format, the share context, and the screen.
If the OpenGL implementation on your system does not support the requested version of OpenGL context, then
QOpenGLContext
will try to create the closest matching version. The actual created context properties can be queried using theQSurfaceFormat
returned by theformat()
function. For example, if you request a context that supports OpenGL 4.3 Core profile but the driver and/or hardware only supports version 3.2 Core profile contexts then you will get a 3.2 Core profile context.Returns
true
if the native context was successfully created and is ready to be used withmakeCurrent()
,swapBuffers()
, etc.Note
If the context already exists, this function destroys the existing context first, and then creates a new one.
See also
- static PySide2.QtGui.QOpenGLContext.currentContext()¶
- Return type:
Returns the last context which called
makeCurrent
in the current thread, orNone
, if no context is current.
- PySide2.QtGui.QOpenGLContext.defaultFramebufferObject()¶
- Return type:
GLuint
Call this to get the default framebuffer object for the current surface.
On some platforms (for instance, iOS) the default framebuffer object depends on the surface being rendered to, and might be different from 0. Thus, instead of calling glBindFramebuffer(0), you should call glBindFramebuffer(ctx->) if you want your application to work across different Qt platforms.
If you use the glBindFramebuffer() in
QOpenGLFunctions
you do not have to worry about this, as it automatically binds the current context’s when 0 is passed.Note
Widgets that render via framebuffer objects, like
QOpenGLWidget
andQQuickWidget
, will override the value returned from this function when painting is active, because at that time the correct “default” framebuffer is the widget’s associated backing framebuffer, not the platform-specific one belonging to the top-level window’s surface. This ensures the expected behavior for this function and other classes relying on it (for example,bindDefault()
orrelease()
).See also
- PySide2.QtGui.QOpenGLContext.doneCurrent()¶
Convenience function for calling
makeCurrent
with a 0 surface.This results in no context being current in the current thread.
See also
- PySide2.QtGui.QOpenGLContext.extensions()¶
- Return type:
Returns the set of OpenGL extensions supported by this context.
The context or a sharing context must be current.
See also
- PySide2.QtGui.QOpenGLContext.extraFunctions()¶
- Return type:
Get the
QOpenGLExtraFunctions
instance for this context.QOpenGLContext
offers this as a convenient way to accessQOpenGLExtraFunctions
without having to manage it manually.The context or a sharing context must be current.
The returned
QOpenGLExtraFunctions
instance is ready to be used and it does not need initializeOpenGLFunctions() to be called.Note
QOpenGLExtraFunctions
contains functionality that is not guaranteed to be available at runtime. Runtime availability depends on the platform, graphics driver, and the OpenGL version requested by the application.See also
- PySide2.QtGui.QOpenGLContext.format()¶
- Return type:
Returns the format of the underlying platform context, if
create()
has been called.Otherwise, returns the requested format.
The requested and the actual format may differ. Requesting a given OpenGL version does not mean the resulting context will target exactly the requested version. It is only guaranteed that the version/profile/options combination for the created context is compatible with the request, as long as the driver is able to provide such a context.
For example, requesting an OpenGL version 3.x core profile context may result in an OpenGL 4.x core profile context. Similarly, a request for OpenGL 2.1 may result in an OpenGL 3.0 context with deprecated functions enabled. Finally, depending on the driver, unsupported versions may result in either a context creation failure or in a context for the highest supported version.
Similar differences are possible in the buffer sizes, for example, the resulting context may have a larger depth buffer than requested. This is perfectly normal.
See also
- PySide2.QtGui.QOpenGLContext.functions()¶
- Return type:
Get the
QOpenGLFunctions
instance for this context.QOpenGLContext
offers this as a convenient way to accessQOpenGLFunctions
without having to manage it manually.The context or a sharing context must be current.
The returned
QOpenGLFunctions
instance is ready to be used and it does not need initializeOpenGLFunctions() to be called.
- Return type:
Returns the application-wide shared OpenGL context, if present. Otherwise, returns
None
.This is useful if you need to upload OpenGL objects (buffers, textures, etc.) before creating or showing a
QOpenGLWidget
orQQuickWidget
.Note
You must set the
AA_ShareOpenGLContexts
flag onQGuiApplication
before creating theQGuiApplication
object, otherwise Qt may not create a global shared context.Warning
Do not attempt to make the context returned by this function current on any surface. Instead, you can create a new context which shares with the global one, and then make the new context current.
See also
AA_ShareOpenGLContexts
setShareContext()
makeCurrent()
- PySide2.QtGui.QOpenGLContext.hasExtension(extension)¶
- Parameters:
extension –
PySide2.QtCore.QByteArray
- Return type:
bool
Returns
true
if this OpenGL context supports the specified OpenGLextension
,false
otherwise.The context or a sharing context must be current.
See also
- PySide2.QtGui.QOpenGLContext.isOpenGLES()¶
- Return type:
bool
Returns true if the context is an OpenGL ES context.
If the context has not yet been created, the result is based on the requested format set via
setFormat()
.See also
- PySide2.QtGui.QOpenGLContext.isValid()¶
- Return type:
bool
Returns if this context is valid, i.e. has been successfully created.
On some platforms the return value of
false
for a context that was successfully created previously indicates that the OpenGL context was lost.The typical way to handle context loss scenarios in applications is to check via this function whenever
makeCurrent()
fails and returnsfalse
. If this function then returnsfalse
, recreate the underlying native OpenGL context by callingcreate()
, callmakeCurrent()
again and then reinitialize all OpenGL resources.On some platforms context loss situations is not something that can avoided. On others however, they may need to be opted-in to. This can be done by enabling
ResetNotification
in theQSurfaceFormat
. This will lead to settingRESET_NOTIFICATION_STRATEGY_EXT
toLOSE_CONTEXT_ON_RESET_EXT
in the underlying native OpenGL context.QOpenGLContext
will then monitor the status viaglGetGraphicsResetStatusEXT()
in everymakeCurrent()
.See also
- PySide2.QtGui.QOpenGLContext.makeCurrent(surface)¶
- Parameters:
surface –
PySide2.QtGui.QSurface
- Return type:
bool
Makes the context current in the current thread, against the given
surface
. Returnstrue
if successful; otherwise returnsfalse
. The latter may happen if the surface is not exposed, or the graphics hardware is not available due to e.g. the application being suspended.If
surface
isNone
this is equivalent to callingdoneCurrent()
.Avoid calling this function from a different thread than the one the
QOpenGLContext
instance lives in. If you wish to useQOpenGLContext
from a different thread you should first make sure it’s not current in the current thread, by callingdoneCurrent()
if necessary. Then callmoveToThread
(otherThread) before using it in the other thread.By default Qt employs a check that enforces the above condition on the thread affinity. It is still possible to disable this check by setting the
Qt::AA_DontCheckOpenGLContextThreadAffinity
application attribute. Be sure to understand the consequences of using QObjects from outside the thread they live in, as explained in theQObject thread affinity
documentation.See also
functions()
doneCurrent()
AA_DontCheckOpenGLContextThreadAffinity
- PySide2.QtGui.QOpenGLContext.nativeHandle()¶
- Return type:
object
Returns the native handle for the context.
This function provides access to the
QOpenGLContext
‘s underlying native context. The returned variant contains a platform-specific value type. These classes can be found in the module QtPlatformHeaders.On platforms where retrieving the native handle is not supported, or if neither
create()
norsetNativeHandle()
was called, a null variant is returned.See also
- static PySide2.QtGui.QOpenGLContext.openGLModuleHandle()¶
- Return type:
void
Returns the platform-specific handle for the OpenGL implementation that is currently in use. (for example, a HMODULE on Windows)
On platforms that do not use dynamic GL switching, the return value is
None
.The library might be GL-only, meaning that windowing system interface functions (for example EGL) may live in another, separate library.
Note
This function requires that the
QGuiApplication
instance is already created.See also
- static PySide2.QtGui.QOpenGLContext.openGLModuleType()¶
- Return type:
Returns the underlying OpenGL implementation type.
On platforms where the OpenGL implementation is not dynamically loaded, the return value is determined during compile time and never changes.
Note
A desktop OpenGL implementation may be capable of creating ES-compatible contexts too. Therefore in most cases it is more appropriate to check
renderableType()
or use the convenience functionisOpenGLES()
.Note
This function requires that the
QGuiApplication
instance is already created.
- PySide2.QtGui.QOpenGLContext.screen()¶
- Return type:
Returns the screen the context was created for.
See also
- PySide2.QtGui.QOpenGLContext.setFormat(format)¶
- Parameters:
format –
PySide2.QtGui.QSurfaceFormat
Sets the
format
the OpenGL context should be compatible with. You need to callcreate()
before it takes effect.When the format is not explicitly set via this function, the format returned by
defaultFormat()
will be used. This means that when having multiple contexts, individual calls to this function can be replaced by one single call tosetDefaultFormat()
before creating the first context.See also
- PySide2.QtGui.QOpenGLContext.setNativeHandle(handle)¶
- Parameters:
handle – object
Set the native handles for this context. When
create()
is called and a native handle is set, configuration settings, likeformat()
, are ignored since thisQOpenGLContext
will wrap an already created native context instead of creating a new one from scratch.On some platforms the native context handle is not sufficient and other related handles (for example, for a window or display) have to be provided in addition. Therefore
handle
is variant containing a platform-specific value type. These classes can be found in the QtPlatformHeaders module.When
create()
is called with native handles set,QOpenGLContext
does not take ownership of the handles, so destroying theQOpenGLContext
does not destroy the native context.Note
Some frameworks track the current context and surfaces internally. Making the adopted
QOpenGLContext
current via Qt will have no effect on such other frameworks’ internal state. Therefore a subsequentmakeCurrent
done via the other framework may have no effect. It is therefore advisable to make explicit calls to make no context and surface current to reset the other frameworks’ internal state after performing OpenGL operations via Qt.Note
Using foreign contexts with Qt windows and Qt contexts with windows and surfaces created by other frameworks may give unexpected results, depending on the platform, due to potential mismatches in context and window pixel formats. To make sure this does not happen, avoid making contexts and surfaces from different frameworks current together. Instead, prefer approaches based on context sharing where OpenGL resources like textures are accessible both from Qt’s and the foreign framework’s contexts.
See also
- PySide2.QtGui.QOpenGLContext.setScreen(screen)¶
- Parameters:
screen –
PySide2.QtGui.QScreen
Sets the
screen
the OpenGL context should be valid for. You need to callcreate()
before it takes effect.See also
- Parameters:
shareContext –
PySide2.QtGui.QOpenGLContext
Makes this context share textures, shaders, and other OpenGL resources with
shareContext
. You need to callcreate()
before it takes effect.See also
- Return type:
Returns the share context this context was created with.
If the underlying platform was not able to support the requested sharing, this will return 0.
See also
- Return type:
Returns the share group this context belongs to.
- static PySide2.QtGui.QOpenGLContext.supportsThreadedOpenGL()¶
- Return type:
bool
Returns
true
if the platform supports OpenGL rendering outside the main (gui) thread.The value is controlled by the platform plugin in use and may also depend on the graphics drivers.
- PySide2.QtGui.QOpenGLContext.surface()¶
- Return type:
Returns the surface the context has been made current with.
This is the surface passed as an argument to
makeCurrent()
.
- PySide2.QtGui.QOpenGLContext.swapBuffers(surface)¶
- Parameters:
surface –
PySide2.QtGui.QSurface
Swap the back and front buffers of
surface
.Call this to finish a frame of OpenGL rendering, and make sure to call
makeCurrent()
again before issuing any further OpenGL commands, for example as part of a new frame.
- PySide2.QtGui.QOpenGLContext.versionFunctions([versionProfile=QOpenGLVersionProfile()])¶
- Parameters:
versionProfile –
PySide2.QtGui.QOpenGLVersionProfile
- Return type:
Returns a pointer to an object that provides access to all functions for the
versionProfile
of this context. There is no need to call as long as this context is current. It is also possible to call this function when the context is not current, but in that case it is the caller’s responsibility to ensure proper initialization by calling afterwards.Usually one would use the template version of this function to automatically have the result cast to the correct type.
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