As a follow-up of my previous experiment with GTK, I’ve finally found some time to resurrect my earlier drafts for QOpenGLWidget sample.
Conventional OCCT samples integrating 3D Viewer into Qt Widgets rely on drawing OpenGL into a native window created by a dedicated QWidget or QGLWidget. Such integration has an important drawback with no other QWidget being able to be drawn on top of 3D Viewer semi-transparently.
A long time ago, Qt 5.4 has introduced another widget class QOpenGLWidget intended to overcome this limitation and to smoothly combine low-level OpenGL-rendered content with Qt-rendered elements. The main trick that QOpenGLWidget does is that it renders OpenGL content not directly into a native window, but into offscreen framebuffer (FBO), which is composite with other Qt elements later on. Such design, however, requires extra efforts in embedding an external 3D engine like OCCT one.
The new sample is almost identical to GTK one described in detail by the previous article. At least, it is very close in the ways it interacts with OCCT 3D Viewer, follows Single Document Interface, redirects events to AIS_ViewController and wraps OpenGL context created by GUI framework, but using Qt-specific APIs.
Some problems have been observed while testing the sample. For instance, dimensions returned by QOpenGLWidget::rect() do not match offscreen FBO created by Qt. In addition, it seems that Qt 5.10+ is required for proper color reproduction in 3D Viewer (or deeper hacks will be necessary to implement):
QSurfaceFormat aGlFormat;
aGlFormat.setColorSpace (QSurfaceFormat::sRGBColorSpace);
QOpenGLWidget::setTextureFormat (GL_SRGB8_ALPHA8);Sample also relies on some improvements in OCCT 7.6.0 (currently in BETA state), so it will not build on older versions without modifications. The sample might be also further improved to implement OpenGL resources cleanup or to check Qt6 compatibility.
Unlimited 3D 