qgs3dmapscene: Fix near/far planes computation once the scene is ready

The near/far planes are computed in `Qgs3DMapScene` when the camera
parameters have changed. However, the near and far planes are not
computed once the scene is ready.
This works well when a new 3d scene is displayed because the camera is
far from the entities and this does affect the near/far planes
computation.
However, when a 3d scene is restored, this does not work if the
entities are close to the camera.

This issue is fixed by using a new logic:
The near and far planes are computed before the scene update to get a
first approximation needed by `updateScene`. Then, `updateScene` is
called. The active nodes may have changed. This can affect the scene
depth. Therefore, once the scene is ready, `updateCameraNearFarPlanes`
is called one more time by `setSceneState` to get an accurate result.

src/3d/qgs3dmapscene.cpp

@@ -314,16 +314,14 @@ void Qgs3DMapScene::onCameraChanged()
     mEngine->camera()->lens()->setOrthographicProjection( -viewWidthFromCenter, viewWidthFromCenter, -viewHeightFromCenter, viewHeightFromCenter, mEngine->camera()->nearPlane(), mEngine->camera()->farPlane() );
   }
 
+  // The near and far planes are computed before the scene update
+  // to get a first approximation needed by `updateScene`.
+  // Then, `updateScene` is called. The active nodes may have changed.
+  // This can affect the scene depth.
+  // Therefore, once the scene is ready, `updateCameraNearFarPlanes`
+  // is called one more time by `setSceneState` to get an accurate result.
+  updateCameraNearFarPlanes();
   updateScene();
-  bool changedCameraPlanes = updateCameraNearFarPlanes();
-
-  if ( changedCameraPlanes )
-  {
-    // repeat update of entities - because we have updated camera's near/far planes,
-    // the active nodes may have changed as well
-    updateScene();
-    updateCameraNearFarPlanes();
-  }
 
   onShadowSettingsChanged();
 
@@ -894,7 +892,14 @@ void Qgs3DMapScene::setSceneState( Qgs3DMapScene::SceneState state )
 {
   if ( mSceneState == state )
     return;
+
   mSceneState = state;
+  if ( mSceneState == SceneState::Ready )
+  {
+    // compute the correct near/far planes once all the entities are loaded
+    updateCameraNearFarPlanes();
+  }
+
   emit sceneStateChanged();
 }
 

tests/src/3d/testqgs3drendering.cpp

@@ -1403,9 +1403,9 @@ void TestQgs3DRendering::testDepthBuffer()
 
   scene->cameraController()->depthBufferCaptured( depthImage );
 
-  QGSCOMPARENEARVECTOR3D( testCam->zoomPoint(), QVector3D( -32.4, 222.8, 184.1 ), 1.0 );
-  QGSCOMPARENEARVECTOR3D( testCam->cameraPose()->centerPoint(), QVector3D( -32.4, 222.8, 184.1 ), 1.0 );
-  QGSCOMPARENEAR( testCam->cameraPose()->distanceFromCenterPoint(), 126.4, 0.1 );
+  QGSCOMPARENEARVECTOR3D( testCam->zoomPoint(), QVector3D( -40.3, 276.8, 228.8 ), 1.0 );
+  QGSCOMPARENEARVECTOR3D( testCam->cameraPose()->centerPoint(), QVector3D( -40.3, 276.8, 228.8 ), 1.0 );
+  QGSCOMPARENEAR( testCam->cameraPose()->distanceFromCenterPoint(), 114.6, 0.1 );
   QCOMPARE( testCam->cumulatedWheelY(), 0 );
 
   // Checking fourth wheel action
@@ -1422,14 +1422,14 @@ void TestQgs3DRendering::testDepthBuffer()
 
   scene->cameraController()->depthBufferCaptured( depthImage );
 
-  QGSCOMPARENEARVECTOR3D( testCam->zoomPoint(), QVector3D( -32.3, 221.7, 183.2 ), 1.0 );
-  QGSCOMPARENEARVECTOR3D( testCam->cameraPose()->centerPoint(), QVector3D( -32.3, 221.7, 183.2 ), 1.0 );
-  QGSCOMPARENEAR( testCam->cameraPose()->distanceFromCenterPoint(), 101.1, 0.1 );
+  QGSCOMPARENEARVECTOR3D( testCam->zoomPoint(), QVector3D( -31.2, 214.4, 177.1 ), 1.0 );
+  QGSCOMPARENEARVECTOR3D( testCam->cameraPose()->centerPoint(), QVector3D( -31.2, 214.4, 177.1 ), 1.0 );
+  QGSCOMPARENEAR( testCam->cameraPose()->distanceFromCenterPoint(), 155.3, 0.1 );
   QCOMPARE( testCam->cumulatedWheelY(), 0 );
 
   // Checking camera position
   QVector3D diff = scene->cameraController()->camera()->position() - startPos;
-  QGSCOMPARENEARVECTOR3D( diff, QVector3D( 125, -850, -700 ), 3.0 );
+  QGSCOMPARENEARVECTOR3D( diff, QVector3D( 119, -816, -674 ), 3.0 );
 
   delete scene;
   mapSettings.setLayers( {} );