Qoffscreensurface

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Qoffscreensurface

QOffscreenSurface Class

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The widget renders fine when visible, but does not when hidden. If I do a show followed by a hide call it works. This seems strange because QOpenGLWidget does internally already render to a framebuffer according to the docs. What is the easiest way to achieve this if possible without creating another framebuffer? Although you might want to wait for this bug to also get fixed Additionally none of the necessary functions initializeGLresizeGL and paintGL are called and none of the functions grabgrabFramebuffer and render are working correctly.

Here is imo a workaround to draw the widget offscreen. You call paintGL directly after setting up all the necessary stuff:. If you want multisampling, you might need a resolve QOpenGLFramebufferObject too, to convert the multisampled framebuffer to a non-multisampled one. Reimplement exposeEventresizeEvent and event you might need to reimplement metric too. A semi-complete implementation:. For offscreen rendering we can use also QOffscreenSurface. Part example with QOffscreenSurface is from here :.

For offscreen rendering, try rendering into a QOpenGLFramebufferObjectwhich can be converted into a QImagewhich in turn can easily be saved to disk. In Qt 5. Learn more. Asked 4 years, 9 months ago. Active 2 years, 8 months ago. Viewed 15k times. Bim Bim 1 1 gold badge 7 7 silver badges 26 26 bronze badges. Active Oldest Votes. Creates a render window.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I am try to do some offscreen rendering jobs in Qt5. Following the instructions of thisI succeeded in offscreen rendering my first pic and outputing it. So to future on, I write an example as the following code and here is a package in Google. I can get the first fbo content and its output file correctly, but from the second time, the fbo was not re-render and it always output the same pictures.

So I want to know what should I do after I finish one time offscreen render to make sure the next time would be correct in qt?

qoffscreensurface

Or is there anyone could tell me how to set animation correctly in QOffscreenSurface? Learn more. How to do dynamic offscreen render with QOffscreenSurface in Qt5 correctly? Ask Question. Asked 2 years, 5 months ago.

Active 2 years, 5 months ago. Viewed 1k times. MartinChan MartinChan 1 3 3 bronze badges. You need to bind the fbo before rendering and release it before you grab the image. Currently you only bind it once through initialize. Botje Thanks firstly and I changed my code like this but it didn't work ,I believe it still has some problems in QOpenGL context setting stuffs. Active Oldest Votes. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password.

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Dark Mode Beta - help us root out low-contrast and un-converted bits. Linked 5. Related Hot Network Questions. Question feed.Threads in an operating system are a very simple thing. Write a function, maybe bundle it with some data and push it onto a newly created thread.

Use a mutex or other method to safely communicate with the thread if necessary. Those who have discovered the joys of the Qt framework may assume that threads in Qt are just like this, and they would be right. However, there are several different ways to use threads in Qt, and it might not be obvious which approach to choose. The article, Multithreading Technologies in Qtcompares the different approaches.

The main thing in this example to keep in mind when using a QThread is that it's not a thread. It's a wrapper around a thread object. This wrapper provides the signals, slots and methods to easily use the thread object within a Qt project. To use it, prepare a QObject subclass with all your desired functionality in it. That's all. We add at least one public slot which will be used to trigger the instance and make it start processing data once the thread has started.

qoffscreensurface

Now, let's see what the implementation for this basic class looks like. While this Worker class doesn't do anything special, it nevertheless contains all the required elements.

It starts processing when its main function, in this case processis called and when it is done it emits the signal finished which will then be used to trigger the shutdown of the QThread instance it is contained in. By the way, one extremely important thing to note here is that you should NEVER allocate heap objects using new in the constructor of the QObject class as this allocation is then performed on the main thread and not on the new QThread instance, meaning that the newly created object is then owned by the main thread and not the QThread instance.

This will make your code fail to work. Instead, allocate such resources in the main function slot such as process in this case as when that is called the object will be on the new thread instance and thus it will own the resource. Now, let's see how to use this new construction by creating a new Worker instance and putting it on a QThread instance:.

The connect series here is the most crucial part. The first connect line hooks up the error message signal from the worker to an error processing function in the main thread. The second connects the thread's started signal to the processing slot in the worker, causing it to start.

Then the clean-up: when the worker instance emits finishedas we did in the example, it will signal the thread to quit, i. We then mark the worker instance using the same finished signal for deletion. Finally, to prevent nasty crashes because the thread hasn't fully shut down yet when it is deleted, we connect the finished of the thread not the worker!The QOffscreenSurface class represents an offscreen surface in the underlying platform.

Even though the surface is typically renderable, the surface's pixels are not accessible. QOffscreenSurface should only be used to create OpenGL resources such as textures or framebuffer objects.

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An application will typically use QOffscreenSurface to perform some time-consuming tasks in a separate thread in order to avoid stalling the main rendering thread.

How the offscreen surface is implemented depends on the underlying platform, but it will typically use a pixel buffer pbuffer. If the platform doesn't implement or support offscreen surfaces, QOffscreenSurface will use an invisible QWindow internally. Note: Due to the fact that QOffscreenSurface is backed by a QWindow on some platforms, cross-platform applications must ensure that create is only called on the main GUI thread.

The QOffscreenSurface is then safe to be used with makeCurrent on other threads, but the initialization and destruction must always happen on the main GUI thread. Note: In order to create an offscreen surface that is guaranteed to be compatible with a given context and window, make sure to set the format to the context's or the window's actual format, that is, the QSurfaceFormat returned from QOpenGLContext::format or QWindow::format after the context or window has been created.

Passing the format returned from QWindow::requestedFormat to setFormat may result in an incompatible offscreen surface since the underlying windowing system interface may offer a different set of configurations for window and pbuffer surfaces.

In this case there will be no underlying native surface. The underlying platform surface is not created until create is called. See also setScreen and create. It is at this point that the surface format set using setFormat gets resolved into an actual native surface. Call destroy to free the platform resources if necessary. After the offscreen surface has been created, this function will return the actual surface format of the surface.

It might differ from the requested format if the requested format could not be fulfilled by the platform. See also setFormatcreateand requestedFormat. Returns true if this offscreen surface is valid; otherwise returns false. If the requested format was not supported by the platform implementation, the requestedFormat will differ from the actual offscreen surface format.

See also setFormat and format. This signal is emitted when an offscreen surface's screen changes, either by being set explicitly with setScreenor automatically when the window's screen is removed. The surface format will be resolved in the create function. Calling this function after create will not re-resolve the surface format of the native surface. See also formatcreateand destroy. The native handle will be resolved in the create function. Calling this function after create will not re-create a native surface.

Note: The interpretation of the native handle is platform specific. Only some platforms will support adopting native handles of offscreen surfaces and platforms that do not implement this support will ignore the handle.

Get Felgo now and join Join Your browser does not seem to support JavaScript. As a result, your viewing experience will be diminished, and you may not be able to execute some actions. Please download a browser that supports JavaScript, or enable it if it's disabled i. I'm having a bit of trouble understanding what the purpose of a QOffscreenSurface is.

Could someone explain exactly how one would go about using an offscreen surface?

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I'm wondering whether it's possible for the new Qt3D framework to render to different widgets as opposed to a full QWindow by using an offscreen surface, since the render aspect expects a QSurface pointer, but I wouldn't really know where to start.

The surface is required when making a context current on a given thread. The implementation will vary depending on a platform, but it will most probably be a pBuffer or a hidden window if pBuffers are not available. The purpose is to provide means of making OpenGL context current on a thread without a need for creating a window for it.

This would usually be something like a worker thread for loading resources or running some non-graphical OpenGL computation. Without QOffscreenSurface you would have to have a window for such thread, which specifically in Qt is problematic, since for example widgets can only be used in the main thread.

Chris-Kawa So if I'm understanding correctly:. In order to use Qt3D, complete with its threaded rendering aspects et al. I'm afraid it's not that simple. Unfortunately OpenGL is for better or worse single threaded. An OpenGL context can be made current in only one thread at a time. If you want to render in multiple threads you have two choices:. An FBO does not belong to a surface. It belongs to an OpenGL context. You can share resources like textures or buffers, but FBOs can't be shared between contexts.

Having said the above, one approach would be to create worker threads, each with its own OpenGL context made current on a QOffscreenSurface, rendering to a texture through an FBO.

These textures would be then used to render them to an FBO in the main thread. Some synchronization will be needed to assure the textures updates are visible in other threads before using them for rendering.

Note however that, as I said earlier, concept of threads has been and, to some degree, still is alien to OpenGL.

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The above scenario will most probably be penalized, as most OpenGL drivers serialize the calls anyway and jump enormous hoops to give you the impression of multi-threading, with varying results.

In many cases single threaded rendering turns out to be faster, mostly due to no need for synchronization. That is however something you will have to heavily profile for your case.

Qt Forum. What exactly is a QOffscreenSurface? This topic has been deleted.Expect failures. Switch to Preprocessed file. For licensing terms. For further. LGPL3 included in the. Please review the following information to. The licenses are as published by the Free Software. Please review the following.

Even though the surface is typically renderable, the surface's pixels are not accessible. An application will typically use QOffscreenSurface to perform some time-consuming tasks in a. Resources created in the. Some common use cases. How the offscreen surface is implemented depends on the underlying platform, but it will.

If the platform doesn't implement or support. The QOffscreenSurface is then safe to be used with.

qoffscreensurface

Passing the format returned from QWindow::requestedFormat to setFormat. In this case there will be no underlying. QSurface :: SurfaceType surfaceType. QSurfaceFormat requestedFormat. The underlying platform surface is not created until create is called. Destroys the offscreen surface.

Returns the surface type of the offscreen surface. Allocates the platform resources associated with the offscreen surface. It is at this point that the surface format set using setFormat gets resolved. Call destroy to free the platform resources if necessary. Releases the native platform resources associated with this offscreen surface. The offscreen surface is valid if the platform resources have been successfuly allocated. The surface format will be resolved in the create function.

Returns the requested surfaceformat of this offscreen surface. If the requested format was not supported by the platform implementation.

This is the value set with setFormat. Returns the actual format of this offscreen surface. After the offscreen surface has been created, this function will return the actual. It might differ from the requested format if the requested. Returns the size of the offscreen surface. QSize QOffscreenSurface :: size const. Returns the screen to which the offscreen surface is connected.The QOffscreenSurface class represents an offscreen surface in the underlying platform.

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Even though the surface is typically renderable, the surface's pixels are not accessible. QOffscreenSurface should only be used to create OpenGL resources such as textures or framebuffer objects.

An application will typically use QOffscreenSurface to perform some time-consuming tasks in a separate thread in order to avoid stalling the main rendering thread.

How the offscreen surface is implemented depends on the underlying platform, but it will typically use a pixel buffer pbuffer. If the platform doesn't implement or support offscreen surfaces, QOffscreenSurface will use an invisible QWindow internally. Note: Due to the fact that QOffscreenSurface is backed by a QWindow on some platforms, cross-platform applications must ensure that create is only called on the main GUI thread.

The QOffscreenSurface is then safe to be used with makeCurrent on other threads, but the initialization and destruction must always happen on the main GUI thread.

Note: In order to create an offscreen surface that is guaranteed to be compatible with a given context and window, make sure to set the format to the context's or the window's actual format, that is, the QSurfaceFormat returned from QOpenGLContext::format or QWindow::format after the context or window has been created. Passing the format returned from QWindow::requestedFormat to setFormat may result in an incompatible offscreen surface since the underlying windowing system interface may offer a different set of configurations for window and pbuffer surfaces.

In this case there will be no underlying native surface. The underlying platform surface is not created until create is called. See also setScreen and create. This signal is emitted when an offscreen surface's screen changes, either by being set explicitly with setScreenor automatically when the window's screen is removed. It is at this point that the surface format set using setFormat gets resolved into an actual native surface.

Call destroy to free the platform resources if necessary. After the offscreen surface has been created, this function will return the actual surface format of the surface. It might differ from the requested format if the requested format could not be fulfilled by the platform. See also setFormatcreateand requestedFormat. Returns true if this offscreen surface is valid; otherwise returns false.

qoffscreensurface

If the requested format was not supported by the platform implementation, the requestedFormat will differ from the actual offscreen surface format. See also setFormat and format. The surface format will be resolved in the create function. Calling this function after create will not re-resolve the surface format of the native surface. See also formatcreateand destroy. The native handle will be resolved in the create function.


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