Fix QEasingCurve possible imprecision at endpoints

Both the spline curves and (most of) the predefines curves are defined
as having start value 0.0 and end value 1.0. The spline and In/OutBack
functions would sometimes not produce that result precisely, so code
could not reliably depend on expressions like (easedValue < 1.0)
becoming false. Fix by explicitly handling endpoints.

Fixes: QTBUG-76781
Fixes: QTBUG-72630
Change-Id: I21be43af469a76c090154bffef8406a9baf2d0b1
Reviewed-by: Thomas Hartmann <thomas.hartmann@qt.io>

1 files changed, 12 insertions, 0 deletions

diff --git a/src/corelib/tools/qeasingcurve.cpp b/src/corelib/tools/qeasingcurve.cpp
index 2ae63fe135..52c8d13fe3 100644
--- a/src/corelib/tools/qeasingcurve.cpp
+++ b/src/corelib/tools/qeasingcurve.cpp
@@ -583,6 +583,13 @@ struct BezierEase : public QEasingCurveFunction
             qWarning("QEasingCurve: Invalid bezier curve");
             return x;
         }
+
+        // The bezier computation is not always precise on the endpoints, so handle explicitly
+        if (!(x > 0))
+            return 0;
+        if (!(x < 1))
+            return 1;
+
         SingleCubicBezier *singleCubicBezier = 0;
         getBezierSegment(singleCubicBezier, x);
 
@@ -998,6 +1005,11 @@ struct BackEase : public QEasingCurveFunction
 
     qreal value(qreal t) override
     {
+        // The *Back() functions are not always precise on the endpoints, so handle explicitly
+        if (!(t > 0))
+            return 0;
+        if (!(t < 1))
+            return 1;
         qreal o = (_o < 0) ? qreal(1.70158) : _o;
         switch(_t) {
         case QEasingCurve::InBack: