Draw QTableView grid lines centered between table cells

We were reserving space between table cells corresponding to one logical
pixel, which on retina screen results in two device pixels. By drawing
the grid line with a cosmetic pen, we were only filling one of these
pixels, leaving space for leftover pixel dust from earlier blits.

By drawing with a non-cosmetic pen of size 1, and ensuring that the grid
line is drawn at the center of the grid, we end up filling the entire
grid line, without overdrawing the table cells.

Change-Id: I7f4d2b27380e5a3d221e265a25f7531fdc4a02b3
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>
(cherry picked from commit 2010df52d4c805557255b90da4aaae8c54c443ea)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

1 files changed, 5 insertions, 3 deletions

diff --git a/src/widgets/itemviews/qtableview.cpp b/src/widgets/itemviews/qtableview.cpp
index 383c4f9fe4..b5c473aa4a 100644
--- a/src/widgets/itemviews/qtableview.cpp
+++ b/src/widgets/itemviews/qtableview.cpp
@@ -1496,7 +1496,7 @@ void QTableView::paintEvent(QPaintEvent *event)
     const int gridSize = showGrid ? 1 : 0;
     const int gridHint = style()->styleHint(QStyle::SH_Table_GridLineColor, &option, this);
     const QColor gridColor = QColor::fromRgba(static_cast<QRgb>(gridHint));
-    const QPen gridPen = QPen(gridColor, 0, d->gridStyle);
+    const QPen gridPen = QPen(gridColor, 1, d->gridStyle);
     const QHeaderView *verticalHeader = d->verticalHeader;
     const QHeaderView *horizontalHeader = d->horizontalHeader;
     const bool alternate = d->alternatingColors;
@@ -1630,7 +1630,8 @@ void QTableView::paintEvent(QPaintEvent *event)
                 int rowY = rowViewportPosition(row);
                 rowY += offset.y();
                 int rowh = rowHeight(row) - gridSize;
-                painter.drawLine(dirtyArea.left(), rowY + rowh, dirtyArea.right(), rowY + rowh);
+                QLineF line(dirtyArea.left(), rowY + rowh, dirtyArea.right(), rowY + rowh);
+                painter.drawLine(line.translated(0.5, 0.5));
             }
 
             // Paint each column
@@ -1642,7 +1643,8 @@ void QTableView::paintEvent(QPaintEvent *event)
                 colp += offset.x();
                 if (!rightToLeft)
                     colp +=  columnWidth(col) - gridSize;
-                painter.drawLine(colp, dirtyArea.top(), colp, dirtyArea.bottom());
+                QLineF line(colp, dirtyArea.top(), colp, dirtyArea.bottom());
+                painter.drawLine(line.translated(0.5, 0.5));
             }
             painter.setPen(old);
         }