Hi, Il 07/03/19 18:33, Stefan Fabian ha scritto:
Today I've found another way to use native OpenGL to draw on top of the scene in OGRE after the render queue ended but couldn't work out how to paint on it using Qt without getting stuck at the getting the content on screen without the QImage copy workaround in Approach 2.
See my talk at QtWS17 about how to integrate Qt Quick 2 with OpenGL. You basically need the third method (QQuickRenderControl) as you don't have control over the GL context creation.
You can wrap a foreign OpenGL context in a QOpenGLContext using its setNativeHandle function. Then you can use QQuickRenderControl as illustrated in my talks, the accompanying code and the examples in Qt.
Unfortunately, 3D graphics and OpenGL is pretty far from my fields of expertise which is why I'm hoping someone who is more competent than me regarding OpenGL and QOpenGL can help me figure this out. I'll attach code parts that I deem important below, if you require a working example I can send you the code (it's not opensource yet but I'm planning on releasing it in the near future) but it requires a Linux distribution (only tested with Ubuntu) and a ROS installation. To summarize: I'm trying to find a way to either render directly to the texture, use a quicker method to copy the content from the FBO to the texture than getting a QImage and memcpy or, alternatively, render directly on top of the scene using the access to native OpenGL I've found today (here the problem is that I don't really know how to continue using OGRE's context when rendering Qt/QML).
An alternative of the above: create yourself a new OpenGL context that shares with the one used by Ogre. Then use this new context (again together with QQRC) to render Qt Quick content into a FBO (see QQuickWindow::setRenderTarget). Now, since your OpenGL context and OGRE's are sharing, the textures that you use inside your FBO are also visible from the OGRE context -- you just need to paint with them, no copies or CPU roundtrips are involved. Just beware of the headaches that go together with sharing OpenGL objects: there's no implicit command synchronization amongst contexts, you must be sure that all your drawing on the texture is fully realized by the GL before reading from it from the other context. Sync objects (or the very crude glFinish) can be used for this.
Hope this helps, -- Giuseppe D'Angelo | giuseppe.dang...@kdab.com | Senior Software Engineer KDAB (France) S.A.S., a KDAB Group company Tel. France +33 (0)4 90 84 08 53, http://www.kdab.com KDAB - The Qt, C++ and OpenGL Experts
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