QQuickVisualTestUtils: fix bug in forEachStep

The calculation for progress was wrong.

With enough steps moving towards a position that's centered over an
item, this wouldn't have been noticeable. However, with only a couple
of steps, it will fail to reach its target.

Before:

    i=0, progress=0
    i=1, progress=0.333333
    i=2, progress=0.666667

After:

    i=0, progress=0
    i=1, progress=0.5
    i=2, progress=1

forEachStep(1, func) is silly: then there is just one step, so we only
call func(1.0) once, and avoid divide-by-zero.

Task-number: QTBUG-105856
Task-number: QTBUG-136031
Pick-to: 6.5 6.8 6.9
Change-Id: Ia8e37e3810ab3e94a17bab6d40087e521f1abde0
Reviewed-by: Shawn Rutledge <[email protected]>

1 files changed, 9 insertions, 1 deletions

diff --git a/src/quicktestutils/quick/visualtestutils_p.h b/src/quicktestutils/quick/visualtestutils_p.h
index 6255222313..edb3b2b56f 100644
--- a/src/quicktestutils/quick/visualtestutils_p.h
+++ b/src/quicktestutils/quick/visualtestutils_p.h
@@ -41,8 +41,16 @@ namespace QQuickVisualTestUtils
     template<typename F>
     void forEachStep(int steps, F &&func)
     {
+        if (steps == 1) {
+            // that's odd usage, but cut to the chase then
+            func(qreal(1));
+            return;
+        }
+
         for (int i = 0; i < steps; ++i) {
-            const qreal progress = qreal(i) / steps;
+            // - 1 because that gives us {0, 0.5, 1} for progress (if steps == 3),
+            // rather than {0, 0.33, 0.66}.
+            const qreal progress = qreal(i) / (steps - 1);
             func(progress);
         }
     }