Gui/Application, QuarterWidget: request OpenGL compatibility profile (#23768)

On Wayland with Qt, the default OpenGL context often ends up being
OpenGL ES. ES is a stricter API based on the "core" profile and lacks
many legacy functions (e.g. glEnd). FreeCAD relies on some of these
functions, which work under Mesa’s permissive stack but fail outright
with NVIDIA’s proprietary drivers, resulting in a blank 3D view.

Fix this by explicitly requesting a desktop OpenGL compatibility
profile both before QApplication creation and in QuarterWidget. This
ensures the presence of the legacy entry points required by Coin/SoQt.

(NB: both requests appear to be necessary; a single change was not
sufficient in testing.)

src/Gui/Application.cpp

@@ -35,6 +35,7 @@
 #include <QScreen>
 #include <QStatusBar>
 #include <QStyle>
+#include <QSurfaceFormat>
 #include <QTextStream>
 #include <QTimer>
 #include <QWindow>
@@ -2383,6 +2384,12 @@ void Application::runApplication()
 {
     StartupProcess::setupApplication();
 
+    QSurfaceFormat fmt;
+    fmt.setRenderableType(QSurfaceFormat::OpenGL);
+    fmt.setProfile(QSurfaceFormat::CompatibilityProfile);
+    fmt.setOption(QSurfaceFormat::DeprecatedFunctions, true);
+    QSurfaceFormat::setDefaultFormat(fmt);
+
     // A new QApplication
     Base::Console().log("Init: Creating Gui::Application and QApplication\n");
 

src/Gui/Quarter/QuarterWidget.cpp

@@ -160,6 +160,15 @@ public:
         //surfaceFormat.setMajorVersion(3);
         //surfaceFormat.setMinorVersion(2);
         //surfaceFormat.setProfile(QSurfaceFormat::CoreProfile);
+
+        // On Wayland, we typically get a core profile unless we explicitly
+        // request a compatibility profile. On llvmpipe, this still seems to
+        // "just work" even if out of spec; on proprietary Nvidia drivers, it
+        // does not.
+        surfaceFormat.setRenderableType(QSurfaceFormat::OpenGL);
+        surfaceFormat.setProfile(QSurfaceFormat::CompatibilityProfile);
+        surfaceFormat.setOption(QSurfaceFormat::DeprecatedFunctions, true);
+
 #if defined (_DEBUG) && 0
         surfaceFormat.setOption(QSurfaceFormat::DebugContext);
 #endif