Change QLineF::setLength() to work whenever length() is non-zero

Previously it only worked when isNull() was false, which is true for
very short lines, even though length() may be non-zero.

[ChangeLog][QtCore][QLineF] QLineF::setLength() will now set the
length if the line's length() is non-zero. Previously, it was
documented to only set the length if isNull() was false; this is a
fuzzy check, so isNull() could be true for a line with non-zero
length().

Fixes: QTBUG-89569
Pick-to: 6.0 5.15
Change-Id: I803e622ad09c85815dde25df8dd3ba6dfcba0714
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

1 files changed, 6 insertions, 5 deletions

diff --git a/src/corelib/tools/qline.cpp b/src/corelib/tools/qline.cpp
index ebcbba0195..1eb645501c 100644
--- a/src/corelib/tools/qline.cpp
+++ b/src/corelib/tools/qline.cpp
@@ -517,12 +517,13 @@ QDataStream &operator>>(QDataStream &stream, QLine &line)
     \fn void QLineF::setLength(qreal length)
 
     Sets the length of the line to the given \a length. QLineF will
-    move the end point - p2() - of the line to give the line its new length.
+    move the end point - p2() - of the line to give the line its new
+    length, unless length() was previously zero, in which case no
+    scaling is attempted. For lines with very short lengths
+    (represented by denormal floating-point values), results may be
+    imprecise.
 
-    A null line will not be rescaled. For non-null lines with very short lengths
-    (represented by denormal floating-point values), results may be imprecise.
-
-    \sa length(), isNull(), unitVector()
+    \sa length(), unitVector()
 */
 
 /*!