Fix dragging 3D view with mouse when camera is far

wonder-sk · wonder-sk · commit a170dcb0a661 · 2017-10-13T09:37:38.000+02:00
Before, when looking at a greater area (e.g. spanning 200km or more),
dragging 3D view with left mouse button would not work at all. Only
when zoomed in more it would start working again.

This was cause by unproject() method in Qt having tolerance against division
by zero very high. Lowering the tolerance by few magnitudes fixed the problem (1e-5 to 1e-10)
diff --git a/src/3d/qgscameracontroller.cpp b/src/3d/qgscameracontroller.cpp
@@ -15,6 +15,8 @@
 
 #include "qgscameracontroller.h"
 
+#include "qgis.h"
+
 #include <Qt3DRender/QObjectPicker>
 #include <Qt3DRender/QPickEvent>
 
@@ -161,6 +163,28 @@ void QgsCameraController::setCameraData( float x, float y, float dist, float pit
 }
 
 
+static QVector3D unproject( const QVector3D &v, const QMatrix4x4 &modelView, const QMatrix4x4 &projection, const QRect &viewport )
+{
+  // Reimplementation of QVector3D::unproject() - see qtbase/src/gui/math3d/qvector3d.cpp
+  // The only difference is that the original implementation uses tolerance 1e-5
+  // (see qFuzzyIsNull()) as a protection against division by zero. For us it is however
+  // common to get lower values (e.g. as low as 1e-8 when zoomed out to the whole Earth with web mercator).
+
+  QMatrix4x4 inverse = QMatrix4x4( projection * modelView ).inverted();
+
+  QVector4D tmp( v, 1.0f );
+  tmp.setX( ( tmp.x() - float( viewport.x() ) ) / float( viewport.width() ) );
+  tmp.setY( ( tmp.y() - float( viewport.y() ) ) / float( viewport.height() ) );
+  tmp = tmp * 2.0f - QVector4D( 1.0f, 1.0f, 1.0f, 1.0f );
+
+  QVector4D obj = inverse * tmp;
+  if ( qgsDoubleNear( obj.w(), 0, 1e-10 ) )
+    obj.setW( 1.0f );
+  obj /= obj.w();
+  return obj.toVector3D();
+}
+
+
 float find_x_on_line( float x0, float y0, float x1, float y1, float y )
 {
   float d_x = x1 - x0;
@@ -172,8 +196,8 @@ float find_x_on_line( float x0, float y0, float x1, float y1, float y )
 QPointF screen_point_to_point_on_plane( const QPointF &pt, const QRect &viewport, Qt3DRender::QCamera *camera, float y )
 {
   // get two points of the ray
-  QVector3D l0 = QVector3D( pt.x(), viewport.height() - pt.y(), 0 ).unproject( camera->viewMatrix(), camera->projectionMatrix(), viewport );
-  QVector3D l1 = QVector3D( pt.x(), viewport.height() - pt.y(), 1 ).unproject( camera->viewMatrix(), camera->projectionMatrix(), viewport );
+  QVector3D l0 = unproject( QVector3D( pt.x(), viewport.height() - pt.y(), 0 ), camera->viewMatrix(), camera->projectionMatrix(), viewport );
+  QVector3D l1 = unproject( QVector3D( pt.x(), viewport.height() - pt.y(), 1 ), camera->viewMatrix(), camera->projectionMatrix(), viewport );
 
   QVector3D p0( 0, y, 0 ); // a point on the plane
   QVector3D n( 0, 1, 0 ); // normal of the plane
