Qt offscreen rendering example
08.10.2020 | by Voodoonris
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. Not sure why, however what I'm trying to do is use offscreen rendering to prepare a complete bitmap ready to blit to the visible context, is there a good simple and complete example of how to do this?
The full strip will be rendered in the offscreen bit map and only the part that matches the displayable screen area for the current heading will be copied to the visible area. Make sure you add quick to the. Learn more. Qt example of using offscreen rendering Ask Question.
Asked 4 years, 1 month ago. Active 4 years, 1 month ago. Viewed times. I am trying to use offscreen rendering in my Qt 5. SPlatten SPlatten 3, 4 4 gold badges 28 28 silver badges 67 67 bronze badges. Just as a basic check, you've got quick in your. I'll move it to the answer from the comments then, for the next person.
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This is not always desirable for more complex scenes. For those the native window based approach shown in basicshapes-cpp will likely be a better choice. To run the example from Qt Creatoropen the Welcome mode and select the example from Examples. For more information, visit Building and Running an Example. Example project code.
Moving the window past the right screen border works though That's not exactly the cleanest way, but is ok for me. Qt Forum. How to render application offscreen and do "screenshot" This topic has been deleted. Only users with topic management privileges can see it. Reply Quote 0 1 Reply Last reply. Any helps will be greatly appreciated. Warning: Calling this function will cause performance problems.
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. 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.Over 90 percent of questions asked here gets answered. If you are looking for information about Qt related issue — register and post your question. You are currently viewing our boards as a guest which gives you limited access to view most discussions and access our other features.
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Results 1 to 4 of 4. Thread: OpenGL rendering in separate thread, Qt 5. Thread Tools Show Printable Version. OpenGL rendering in separate thread, Qt 5. It doesn't work on 5. Also it is complaining a lot in the application output like this: QGLShader::link: " 45,20 : warning X implicit truncation of vector type QWidget::repaint: It is dangerous to leave painters active on a widget outside of the PaintEvent QBackingStore::flush called with non-exposed window, behavior is undefined QGLShader::link: " 45,20 : warning X implicit truncation of vector type QWidget::repaint: It is dangerous to leave painters active on a widget outside of the PaintEvent etc etc.
I wander is it possible to make it work stable?
Was it supposed to be enough in Qt 5. I attached the hypnotizer demo with changes mentioned. Attached Files hypnotizer. Re: OpenGL rendering in separate thread, Qt 5. I found that as long as I had a primary context on the main thread, regardless of whether or not I actually used it, I could have multiple windows open, shared context or not.
I could subsequently close any window except the one using the main context. If I closed that one, the program crashes. I'm also curious what the 'intended' behavior of this demo is, and I am very anxious to arrive at the optimal solution to this problem.
Join Date Jun Posts 1. I'd love to hear an update for this as well. I'm just trying to get the example to work at this point for a proof of concept that rendering can be done on a separate thread while still using a QPainter. I am just trying to render a QImage, since we'll be rendering video. Attaching my own project.GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together. If nothing happens, download GitHub Desktop and try again.
If nothing happens, download Xcode and try again. If nothing happens, download the GitHub extension for Visual Studio and try again. To get the image to resize adjust the OffscreenEngines rendering size on resize of the widget.
I guess the rest should be self-explanatory. This is supposed to show how to construct an offline framegraph and save everyone who needs such a renderer the hours of trial and error and the despair I encountered. Somehow the first image that is captured is blank and without rendered objects. I suspected the problem to be that the render capture was triggered right after the clear buffers node. But it doesn't seem to have any effect when we place the capture node anywhere else.
So basically the first image has to be skipped. To enable depth tests just add a QRenderStateSet as a child to the camera selector and a QDepthTest as a child to the render state set and add it as a state. Then, in the render target add a texture to the depth attatchment point. This is it. If maybe someone gets it running they can fork the project and I can then do a pull. For further information read the copyright notice in the source code. Skip to content. Dismiss Join GitHub today GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together.
Sign up. Branch: master. Find file. Sign in Sign up. Go back. Launching Xcode If nothing happens, download Xcode and try again. Latest commit. Sorry I only just saw your request, it's looking good.
If you have more comments just create a new pull request, I mainly commented the code for myself and some things might not be clear to others ; Cheers. Latest commit fdf Jul 12, You signed in with another tab or window. Reload to refresh your session. You signed out in another tab or window. Initial commit. Jan 5, Add a note about minimum Qt version. Jun 26, Fixed an irritating typo. Feb 10, This class is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.
Rendering into a pbuffer is normally done using full hardware acceleration. This can be significantly faster than rendering into a QPixmap. As of Qt 4. Note that OpenGL 2. Constructs an OpenGL pbuffer with the width and height. If no format is specified, the default format is used. If you intend to bind this pbuffer as a dynamic texture, the width and height components of size must be powers of two e.
See also size and format. Constructs an OpenGL pbuffer of the given size. Generates and binds a 2D GL texture to the current context, based on image. The generated texture id is returned and can be used in later glBindTexture calls. Returns true on success; otherwise returns false. To unbind the texture, call releaseFromDynamicTexture. While the texture is bound, it is updated automatically when the pbuffer contents change, eliminating the need for additional copy operations. An alternative that works on all systems including X11 is to manually copy the pbuffer contents to a texture using updateDynamicTexture.
Makes no context the current OpenGL context. Draws the given texture, textureIdto the given target rectangle, targetin OpenGL model space. The textureTarget should be a 2D texture target. Draws the given texture, textureIdat the given point in OpenGL model space.