From bcb3c189a17e5d6894f1676fb404bc0adfd0f3d8 Mon Sep 17 00:00:00 2001
From: Dario Sassi <dario.sassi@egalware.com>
Date: Thu, 22 Jan 2026 11:00:44 +0100
Subject: [PATCH] EgtGraphics : - migliorato calcolo centro di vista in Zwin
 utilizzando GetPixelZ.

---
 Scene.h         |  1 +
 SceneBasic.cpp  | 18 ++++++++++++++++++
 SceneCamera.cpp |  6 +++++-
 3 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/Scene.h b/Scene.h
index 86a01f9..deaa245 100644
--- a/Scene.h
+++ b/Scene.h
@@ -246,6 +246,7 @@ class Scene : public IEGrScene
       bool MyDraw( bool bSwapBF) ;
       bool Background( void) ;
       bool Prepare( void) ;
+      bool GetPixelZ( const Point3d& ptWin, double& dWinZ) ;
      // Camera
       bool VerifyCamera( bool bUseOrizzOffsCamera = false) ;
       bool CalcDirUp( bool bUseOrizzOffsCamera = false) ;
diff --git a/SceneBasic.cpp b/SceneBasic.cpp
index c38e892..ddfbb2d 100644
--- a/SceneBasic.cpp
+++ b/SceneBasic.cpp
@@ -941,6 +941,24 @@ Scene::UnProject( const Point3d& ptView, Point3d& ptWorld) const
    return ( nRes == GL_TRUE) ;
 }
 
+//----------------------------------------------------------------------------
+bool
+Scene::GetPixelZ( const Point3d& ptWin, double& dWinZ)
+{
+   glGetError() ;
+   GLint Viewport[ 4] ;
+   glGetIntegerv( GL_VIEWPORT, Viewport) ;
+   float dZ ;
+   glReadBuffer( GL_FRONT) ;
+   glReadPixels( int( ptWin.x), Viewport[3] - int( ptWin.y), 1, 1, GL_DEPTH_COMPONENT, GL_FLOAT, &dZ) ;
+   if ( glGetError() == GL_NO_ERROR  &&  dZ > 0.001  &&  dZ < 0.999) {
+      dWinZ = dZ ;
+      return true ;
+   }
+   dWinZ = GetProjectedCenter().z ;
+   return false ;
+}
+
 //----------------------------------------------------------------------------
 void
 Scene::Destroy( void)
diff --git a/SceneCamera.cpp b/SceneCamera.cpp
index 768c4ba..74b0597 100644
--- a/SceneCamera.cpp
+++ b/SceneCamera.cpp
@@ -525,8 +525,12 @@ Scene::ZoomChange( double dCoeff)
 bool
 Scene::ZoomOnPoint( const Point3d& ptWin, double dCoeff)
 {
+  // leggo Z del pixel
+   double dWinZ ;
+   GetPixelZ( ptWin, dWinZ) ;
+
   // porto il punto in coordinate mondo
-   Point3d ptView( ptWin.x, ptWin.y, GetProjectedCenter().z) ;
+   Point3d ptView( ptWin.x, ptWin.y, dWinZ) ;
    Point3d ptWorld ;
    if ( ! UnProject( ptView, ptWorld))
       return false ;