Painting: handle large and negative dash offset values

The mapping of the dash offset into the dash pattern was susceptible
to int overflow.

Change-Id: I254ed40b323ef516d10abc8e6008b14cfc23d2a0
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>
(cherry picked from commit ca604964f651b71f2b2a45a65e741167f520b714)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

1 files changed, 3 insertions, 2 deletions

diff --git a/src/gui/painting/qpaintengine_raster.cpp b/src/gui/painting/qpaintengine_raster.cpp
index e3444e6229..b589526b4f 100644
--- a/src/gui/painting/qpaintengine_raster.cpp
+++ b/src/gui/painting/qpaintengine_raster.cpp
@@ -1633,8 +1633,9 @@ void QRasterPaintEngine::stroke(const QVectorPath &path, const QPen &pen)
             patternLength += pattern.at(i);
 
         if (patternLength > 0) {
-            int n = qFloor(dashOffset / patternLength);
-            dashOffset -= n * patternLength;
+            dashOffset = std::fmod(dashOffset, patternLength);
+            if (dashOffset < 0)
+                dashOffset += patternLength;
             while (dashOffset >= pattern.at(dashIndex)) {
                 dashOffset -= pattern.at(dashIndex);
                 if (++dashIndex >= pattern.size())