Raster painting: fix dashing for separate lines

When drawing multiple distinct (unconnected) lines (e.g. from
QPainter::drawLines() or a QPainterPath with alternating
movetos/linetos), the dash pattern should not continue from one to the
next, as it should when drawing a connected line (e.g. polyline).
Both the cosmetic stroker and the full stroker does it right, but the
fast rasterizing codepath got it wrong.

Fixes: QTBUG-83048
Change-Id: I3d090f7121726755a0e53cb66b99a5563ac0e1c0
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

src/gui/painting/qpaintengine_raster.cpp

@@ -1713,8 +1713,11 @@ void QRasterPaintEngine::stroke(const QVectorPath &path, const QPen &pen)
                                             width / line.length(),
                                             s->lastPen.capStyle() == Qt::SquareCap);
             } else {
-                d->rasterizeLine_dashed(line, width,
-                                        &dashIndex, &dashOffset, &inDash);
+                // LinesHint means each line is distinct, so restart dashing
+                int dIndex = dashIndex;
+                qreal dOffset = dashOffset;
+                bool inD = inDash;
+                d->rasterizeLine_dashed(line, width, &dIndex, &dOffset, &inD);
             }
         }
     }

tests/auto/other/lancelot/scripts/linedashes.qps

@@ -92,3 +92,41 @@ repeat_block draw_lines
 setPen 0xffff0000 0 dashline squarecap
 translate 100 0
 repeat_block draw_lines
+
+path_moveTo mypath 10 10
+path_lineTo mypath 87 10
+path_moveTo mypath 10 30
+path_lineTo mypath 87 30
+path_moveTo mypath 10 50
+path_lineTo mypath 87 50
+
+resetMatrix
+translate 0 150
+
+begin_block distinctLines
+
+setPen black 0 SolidLine SquareCap
+pen_setDashPattern [ 3 3 ]
+drawPath mypath
+
+translate 100 0
+setPen black 5 SolidLine SquareCap
+pen_setDashPattern [ 3 3 ]
+drawPath mypath
+
+translate 100 0
+setPen black 0 SolidLine RoundCap
+pen_setDashPattern [ 3 3 ]
+drawPath mypath
+
+translate 100 0
+setPen black 5 SolidLine RoundCap
+pen_setDashPattern [ 3 3 ]
+drawPath mypath
+
+end_block distinctLines
+
+resetMatrix
+translate 0 220
+setRenderHint Antialiasing true
+repeat_block distinctLines