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
Change-Id: I803e622ad09c85815dde25df8dd3ba6dfcba0714
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
(cherry picked from commit 6974737695eae5a41bc8a3f344a4f1f199006f21)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

1 files changed, 7 insertions, 7 deletions

diff --git a/tests/auto/corelib/tools/qline/tst_qline.cpp b/tests/auto/corelib/tools/qline/tst_qline.cpp
index f4ac51fc24..9d5df728a1 100644
--- a/tests/auto/corelib/tools/qline/tst_qline.cpp
+++ b/tests/auto/corelib/tools/qline/tst_qline.cpp
@@ -247,8 +247,8 @@ void tst_QLine::testLength_data()
         << -(tiny * .5) << -(tiny * .5) << (tiny * .5) << (tiny * .5)
         << (tiny * M_SQRT2) << (2 * M_SQRT2) << 2.0 << 2.0;
     QTest::newRow("[1+3e-13,1+4e-13]|1895| (1, 1)")
-        << 1.0 << 1.0 << (1 + 3e-13) << (1 + 4e-13) // isNull(), so ignores setLength()
-        << 5e-13 << 1895.0 << 3e-13 << 4e-13;
+        << 1.0 << 1.0 << (1 + 3e-13) << (1 + 4e-13)
+        << 5e-13 << 1895.0 << 1137.0 << 1516.0;
     QTest::newRow("[4e-323,5e-324]|1892|") // Unavoidable underflow: denormals
         << 0.0 << 0.0 << 4e-323 << 5e-324
         << 4e-323 << 1892.0 << 4e-323 << 5e-324; // vx, vy values ignored
@@ -266,14 +266,14 @@ void tst_QLine::testLength()
     QFETCH(double, vy);
 
     QLineF l(x1, y1, x2, y2);
-    const bool wasNull = l.isNull();
-    if (!wasNull)
-        QCOMPARE(l.length(), qreal(length));
+    QCOMPARE(l.length(), qreal(length));
 
     l.setLength(lengthToSet);
-    QCOMPARE(l.length(), wasNull ? qreal(length) : qreal(lengthToSet));
     // Scaling tiny values up to big can be imprecise: don't try to test vx, vy
-    if (wasNull || !qFuzzyIsNull(length)) {
+    if (length > 0 && qFuzzyIsNull(length)) {
+        QVERIFY(l.length() > lengthToSet / 2 && l.length() < lengthToSet * 2);
+    } else {
+        QCOMPARE(l.length(), length > 0 ? qreal(lengthToSet) : qreal(length));
         QCOMPARE(l.dx(), qreal(vx));
         QCOMPARE(l.dy(), qreal(vy));
     }