+ Improve mesh selection (precompute projection matrix and use polygon bounding box)

src/Gui/Utilities.cpp

@@ -51,6 +51,7 @@ Base::Vector3f ViewVolumeProjection::operator()(const Base::Vector3f &pt) const
         pt3d.setValue(ptt.x, ptt.y, ptt.z);
     }
 
+    // Calling this function is expensive as the complete projection matrix is recomputed on each step
     viewVolume.projectToScreen(pt3d,pt3d);
     return Base::Vector3f(pt3d[0],pt3d[1],pt3d[2]);
 }
@@ -101,12 +102,26 @@ Base::Matrix4D ViewVolumeProjection::getProjectionMatrix () const
     // Inventor stores the transposed matrix
     Base::Matrix4D mat;
     SbMatrix affine, proj;
+
+    // The Inventor projection matrix is obtained by multiplying both matrices together (cf source)
     viewVolume.getMatrices(affine, proj);
+    SbMatrix pmatrix = affine.multRight(proj);
+
     for (int i=0; i<4; i++) {
         for (int j=0; j<4; j++)
-            mat[i][j] = proj[j][i];
+            mat[i][j] = pmatrix[j][i];
     }
 
+    // Compose the object transform, if defined
+    if (hasTransform) {
+        mat = mat * transform;
+    }
+
+    // Scale from [-1,1] to [0,1]
+    // As done in OpenInventor sources (see SbDPViewVolume::projectToScreen)
+    mat.scale(0.5, 0.5, 0.5);
+    mat.move(0.5, 0.5, 0.5);
+
     return mat;
 }