Fix the rendering of lines with the X11 paint engine

On the X11 paint engine, when rendering lines with float coordinates,
the lines were one pixel off if the decimal was > 0.5.

This fixes the WebKit bug https://bugs.webkit.org/show_bug.cgi?id=42248

Autotest by Yoann Lopes.

Reviewed-by: Simon Hausmann
Reviewed-by: Yoann Lopes
Reviewed-by: Andreas Kling

1 files changed, 10 insertions, 12 deletions

diff --git a/src/gui/painting/qpaintengine_x11.cpp b/src/gui/painting/qpaintengine_x11.cpp
index 910b2df..e521e01 100644
--- a/src/gui/painting/qpaintengine_x11.cpp
+++ b/src/gui/painting/qpaintengine_x11.cpp
@@ -696,11 +696,10 @@ void QX11PaintEngine::drawLines(const QLine *lines, int lineCount)
                 linef = d->matrix.map(QLineF(lines[i]));
             }
             if (clipLine(&linef, d->polygonClipper.boundingRect())) {
-                int x1 = qRound(linef.x1() + aliasedCoordinateDelta);
-                int y1 = qRound(linef.y1() + aliasedCoordinateDelta);
-                int x2 = qRound(linef.x2() + aliasedCoordinateDelta);
-                int y2 = qRound(linef.y2() + aliasedCoordinateDelta);
-
+                int x1 = qFloor(linef.x1() + aliasedCoordinateDelta);
+                int y1 = qFloor(linef.y1() + aliasedCoordinateDelta);
+                int x2 = qFloor(linef.x2() + aliasedCoordinateDelta);
+                int y2 = qFloor(linef.y2() + aliasedCoordinateDelta);
                 XDrawLine(d->dpy, d->hd, d->gc, x1, y1, x2, y2);
             }
         }
@@ -730,11 +729,10 @@ void QX11PaintEngine::drawLines(const QLineF *lines, int lineCount)
         for (int i = 0; i < lineCount; ++i) {
             QLineF linef = d->matrix.map(lines[i]);
             if (clipLine(&linef, d->polygonClipper.boundingRect())) {
-                int x1 = qRound(linef.x1() + aliasedCoordinateDelta);
-                int y1 = qRound(linef.y1() + aliasedCoordinateDelta);
-                int x2 = qRound(linef.x2() + aliasedCoordinateDelta);
-                int y2 = qRound(linef.y2() + aliasedCoordinateDelta);
-
+                int x1 = qFloor(linef.x1() + aliasedCoordinateDelta);
+                int y1 = qFloor(linef.y1() + aliasedCoordinateDelta);
+                int x2 = qFloor(linef.x2() + aliasedCoordinateDelta);
+                int y2 = qFloor(linef.y2() + aliasedCoordinateDelta);
                 XDrawLine(d->dpy, d->hd, d->gc, x1, y1, x2, y2);
             }
         }
@@ -1690,8 +1688,8 @@ void QX11PaintEnginePrivate::strokePolygon_dev(const QPointF *polygonPoints, int
     if (clippedCount > 0) {
         QVarLengthArray<XPoint> xpoints(clippedCount);
         for (int i = 0; i < clippedCount; ++i) {
-            xpoints[i].x = qRound(clippedPoints[i].x + aliasedCoordinateDelta);
-            xpoints[i].y = qRound(clippedPoints[i].y + aliasedCoordinateDelta);
+            xpoints[i].x = qFloor(clippedPoints[i].x + aliasedCoordinateDelta);
+            xpoints[i].y = qFloor(clippedPoints[i].y + aliasedCoordinateDelta);
         }
         uint numberPoints = qMin(clippedCount, xlibMaxLinePoints);
         XPoint *pts = xpoints.data();