qgs3dmapscene: Compute max clip planes

The number of available clip planes depends on the OpenGL
implementation.

This change Introduces a new function in Qgs3DUtils function called
`Qgs3DUtils::getOpenGLMaxClipPlanes` to compute this
number (`GL_MAX_CLIP_PLANES`) and use it in the 3D scene.

See: https://registry.khronos.org/OpenGL-Refpages/gl2.1/xhtml/glClipPlane.xml

python/3d/auto_generated/qgs3dmapscene.sip.in

@@ -160,9 +160,9 @@ In mathematical terms, a 3d plane can be defined with the equation ``ax+by+cz+d=
 The normal is ``(a, b, c)`` with ``|a, b, c| = 1``
 The distance is ``-d``.
 
-By default, OpenGL supports up to 8 additional clipping planes. If ``clipPlaneEquations``
-contains more than 8 planes, only the first 8 ones will be used.
-If ``clipPlaneEquations`` is empty, the clipping is disabled.
+The number of available clip planes depends on the OpenGL implementation. It should at least handle
+6 additional clip planes. When the map scene is created, this number is retrieved.
+If, ``clipPlaneEquations`` contains more than this maximum, only the first ones will be kept.
 
 .. seealso:: :py:func:`disableClipping`
 

python/PyQt6/3d/auto_generated/qgs3dmapscene.sip.in

@@ -160,9 +160,9 @@ In mathematical terms, a 3d plane can be defined with the equation ``ax+by+cz+d=
 The normal is ``(a, b, c)`` with ``|a, b, c| = 1``
 The distance is ``-d``.
 
-By default, OpenGL supports up to 8 additional clipping planes. If ``clipPlaneEquations``
-contains more than 8 planes, only the first 8 ones will be used.
-If ``clipPlaneEquations`` is empty, the clipping is disabled.
+The number of available clip planes depends on the OpenGL implementation. It should at least handle
+6 additional clip planes. When the map scene is created, this number is retrieved.
+If, ``clipPlaneEquations`` contains more than this maximum, only the first ones will be kept.
 
 .. seealso:: :py:func:`disableClipping`
 

src/3d/qgs3dmapscene.cpp

@@ -99,6 +99,9 @@ Qgs3DMapScene::Qgs3DMapScene( Qgs3DMapSettings &map, QgsAbstract3DEngine *engine
 
   QRect viewportRect( QPoint( 0, 0 ), mEngine->size() );
 
+  // Get the maximum of clip planes available
+  mMaxClipPlanes = Qgs3DUtils::getOpenGLMaxClipPlanes();
+
   // Camera
   float aspectRatio = ( float )viewportRect.width() / viewportRect.height();
   mEngine->camera()->lens()->setPerspectiveProjection( mMap.fieldOfView(), aspectRatio, 10.f, 10000.0f );
@@ -1223,11 +1226,11 @@ void Qgs3DMapScene::handleClippingOnAllEntities() const
 
 void Qgs3DMapScene::enableClipping( const QList<QVector4D> &clipPlaneEquations )
 {
-  if ( clipPlaneEquations.size() > 8 )
+  if ( clipPlaneEquations.size() > mMaxClipPlanes )
   {
-    QgsDebugMsgLevel( QStringLiteral( "Qgs3DMapScene::enableClipping: it is not possible to use more than 8 clipping planes." ), 2 );
+    QgsDebugMsgLevel( QStringLiteral( "Qgs3DMapScene::enableClipping: it is not possible to use more than %s clipping planes." ).arg( QString::number( mMaxClipPlanes ) ), 2 );
   }
-  mClipPlanesEquations = clipPlaneEquations.mid( 0, 8 );
+  mClipPlanesEquations = clipPlaneEquations.mid( 0, mMaxClipPlanes );
 
   // enable the clip planes on the framegraph
   QgsFrameGraph *frameGraph = mEngine->frameGraph();

src/3d/qgs3dmapscene.h

@@ -227,9 +227,9 @@ class _3D_EXPORT Qgs3DMapScene : public QObject
      * The normal is ``(a, b, c)`` with ``|a, b, c| = 1``
      * The distance is ``-d``.
      *
-     * By default, OpenGL supports up to 8 additional clipping planes. If \a clipPlaneEquations
-     * contains more than 8 planes, only the first 8 ones will be used.
-     * If \a clipPlaneEquations is empty, the clipping is disabled.
+     * The number of available clip planes depends on the OpenGL implementation. It should at least handle
+     * 6 additional clip planes. When the map scene is created, this number is retrieved.
+     * If, \a clipPlaneEquations contains more than this maximum, only the first ones will be kept.
      *
      * \see disableClipping()
      * \since QGIS 3.40
@@ -357,6 +357,7 @@ class _3D_EXPORT Qgs3DMapScene : public QObject
     bool mSceneUpdatesEnabled = true;
 
     QList<QVector4D> mClipPlanesEquations;
+    int mMaxClipPlanes;
 
 };
 #endif // QGS3DMAPSCENE_H

src/3d/qgs3dutils.cpp

@@ -42,6 +42,10 @@
 #include <QtMath>
 #include <Qt3DExtras/QPhongMaterial>
 #include <Qt3DRender/QRenderSettings>
+#include <QOffscreenSurface>
+#include <QOpenGLContext>
+#include <QOpenGLFunctions>
+
 
 #if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
 #include <Qt3DRender/QBuffer>
@@ -952,3 +956,25 @@ QByteArray Qgs3DUtils::removeDefinesFromShaderCode( const QByteArray &shaderCode
 
   return newShaderCode;
 }
+
+int Qgs3DUtils::getOpenGLMaxClipPlanes()
+{
+  int nrPlanes = 6;
+
+  QOffscreenSurface offscreen;
+  QOpenGLContext context;
+
+  offscreen.setFormat( QSurfaceFormat::defaultFormat() );
+  offscreen.create();
+  Q_ASSERT_X( offscreen.isValid(), Q_FUNC_INFO, "Unable to create offscreen surface to gather capabilities" );
+
+  context.setFormat( QSurfaceFormat::defaultFormat() );
+  if ( context.create() )
+  {
+    context.makeCurrent( &offscreen );
+    auto funcs = context.functions();
+    funcs->glGetIntegerv( GL_MAX_CLIP_PLANES, &nrPlanes );
+  }
+
+  return nrPlanes;
+}

src/3d/qgs3dutils.h

@@ -331,6 +331,14 @@ class _3D_EXPORT Qgs3DUtils
      * \since QGIS 3.40
      */
     static QByteArray removeDefinesFromShaderCode( const QByteArray &shaderCode, const QStringList &defines );
+
+    /**
+     * Gets the maximum number of clip planes that can be used.
+     * This value depends on the OpenGL implementation. It should be at least 6.
+     *
+     * \since QGIS 3.42
+     */
+    static int getOpenGLMaxClipPlanes();
 };
 
 #endif // QGS3DUTILS_H