Reset buffered GridOffset(s) for suspicious values

Huge offsets of GridOffset(s) are a hint for error -> usually the
conditions for calculation have changed. E.g. - I saw errors with
+/-5740, that was in the environment of massive external UNO API
using LO as target.
If condtions for this calculation change, it is usually required to
call
- ViewObjectContact::resetGridOffset(), or
- ObjectContact::resetAllGridOffsets() or
- ScDrawView::resetGridOffsetsForAllSdrPageViews()
as it is done e.g. when zoom changes (see ScDrawView::RecalcScale()).
Theoretically these resets have to be done for any precondition
changed that is used in the calculation of that value (see
ScDrawView::calculateGridOffsetForSdrObject).
This is not complete and would be hard to do so. Since it is just a
buffered value and re-calculation is not expensive (linear O(n)) we
can just reset suspicious values here  what fixes the problem.
Hopefully - when that non-linear ViewTransformation problem for the
calc-view gets solved one day - all this can be removed again. For
now, let's just reset here and force re-calculation.
Added a SAL_WARN to inform about this, too.

Change-Id: I09137f7703fd00c2351a288a40bf87a2691ba6e3
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/155983
Tested-by: Jenkins
Reviewed-by: Armin Le Grand <Armin.Le.Grand@me.com>

1 files changed, 32 insertions, 3 deletions

diff --git a/svx/source/sdr/contact/viewobjectcontact.cxx b/svx/source/sdr/contact/viewobjectcontact.cxx
index d15ba27dd9f9..7191743188e1 100644
--- a/svx/source/sdr/contact/viewobjectcontact.cxx
+++ b/svx/source/sdr/contact/viewobjectcontact.cxx
@@ -461,10 +461,39 @@ drawinglayer::primitive2d::Primitive2DContainer ViewObjectContact::getPrimitive2
 // (->View) that has then all needed information
 const basegfx::B2DVector& ViewObjectContact::getGridOffset() const
 {
-    if(0.0 == maGridOffset.getX() && 0.0 == maGridOffset.getY() && GetObjectContact().supportsGridOffsets())
+    if (GetObjectContact().supportsGridOffsets())
     {
-        // create on-demand
-        GetObjectContact().calculateGridOffsetForViewOjectContact(const_cast<ViewObjectContact*>(this)->maGridOffset, *this);
+        if (fabs(maGridOffset.getX()) > 1000.0)
+        {
+            // Huge offsets are a hint for error -> usually the conditions for
+            // calculation have changed. E.g. - I saw errors with +/-5740, that
+            // was in the environment of massive external UNO API using LO as
+            // target.
+            // If condtions for this calculation change, it is usually required to call
+            // - ViewObjectContact::resetGridOffset(), or
+            // - ObjectContact::resetAllGridOffsets() or
+            // - ScDrawView::resetGridOffsetsForAllSdrPageViews()
+            // as it is done e.g. when zoom changes (see ScDrawView::RecalcScale()).
+            // Theoretically these resets have to be done for any precondition
+            // changed that is used in the calculation of that value (see
+            // ScDrawView::calculateGridOffsetForSdrObject).
+            // This is not complete and would be hard to do so.
+            // Since it is just a buffered value and re-calculation is not
+            // expensive (linear O(n)) we can just reset suspicious values here.
+            // Hopefully - when that non-linear ViewTransformation problem for
+            // the calc-view gets solved one day - all this can be removed
+            // again. For now, let's just reset here and force re-calculation.
+            // Add a SAL_WARN to inform about this.
+            SAL_WARN("svx", "Suspicious GridOffset value resetted (!)");
+            const_cast<ViewObjectContact*>(this)->maGridOffset.setX(0.0);
+            const_cast<ViewObjectContact*>(this)->maGridOffset.setY(0.0);
+        }
+
+        if(0.0 == maGridOffset.getX() && 0.0 == maGridOffset.getY() && GetObjectContact().supportsGridOffsets())
+        {
+            // create on-demand
+            GetObjectContact().calculateGridOffsetForViewOjectContact(const_cast<ViewObjectContact*>(this)->maGridOffset, *this);
+        }
     }
 
     return maGridOffset;