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authorNils Jeisecke <jeisecke@saltation.de>2015-06-05 17:48:00 +0200
committerAndy Shaw <andy.shaw@qt.io>2017-09-07 20:40:14 +0200
commit87748cc18e6a0d9e65933aa2462dc78ab8f9f22e (patch)
tree82fa4b8e8fdcddf3fcdeea5fd8aad2a07cb22034 /src/gui/text/qtextdocumentlayout.cpp
parent20e9422e069a27b7e29b54207447e6ca02b3a55a (diff)
QTextDocumentLayout: Avoid table border drawing artifacts
As borders are always painted for single cells any rounding errors that occur when mapping from fixed point numbers to integers during raster painting will cause ugly drawing artifacts like extra pixels between cells or borders that overlap. To avoid this the following values are being rounded: - table offset - column positions and widths - row positions and cell heights For the column positions and widths the distribution constraints (total table width) are respected. Task-number: QTBUG-43589 Change-Id: I6308c113f8f9be3db8e9267629f26b5d65d2d7c7 Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>
Diffstat (limited to 'src/gui/text/qtextdocumentlayout.cpp')
-rw-r--r--src/gui/text/qtextdocumentlayout.cpp24
1 files changed, 20 insertions, 4 deletions
diff --git a/src/gui/text/qtextdocumentlayout.cpp b/src/gui/text/qtextdocumentlayout.cpp
index 7873faf2cb..e5cfa7f46e 100644
--- a/src/gui/text/qtextdocumentlayout.cpp
+++ b/src/gui/text/qtextdocumentlayout.cpp
@@ -931,7 +931,10 @@ void QTextDocumentLayoutPrivate::drawFrame(const QPointF &offset, QPainter *pain
Q_ASSERT(!fd->sizeDirty);
Q_ASSERT(!fd->layoutDirty);
- const QPointF off = offset + fd->position.toPointF();
+ // floor the offset to avoid painting artefacts when drawing adjacent borders
+ // we later also round table cell heights and widths
+ const QPointF off = QPointF(QPointF(offset + fd->position.toPointF()).toPoint());
+
if (context.clip.isValid()
&& (off.y() > context.clip.bottom() || off.y() + fd->size.height.toReal() < context.clip.top()
|| off.x() > context.clip.right() || off.x() + fd->size.width.toReal() < context.clip.left()))
@@ -1681,7 +1684,8 @@ recalc_minmax_widths:
for (int n = 0; n < cspan; ++n) {
const int col = i + n;
QFixed w = widthToDistribute / (cspan - n);
- td->minWidths[col] = qMax(td->minWidths.at(col), w);
+ // ceil to avoid going below minWidth when rounding all column widths later
+ td->minWidths[col] = qMax(td->minWidths.at(col), w).ceil();
widthToDistribute -= td->minWidths.at(col);
if (widthToDistribute <= 0)
break;
@@ -1787,6 +1791,18 @@ recalc_minmax_widths:
}
}
+ // in order to get a correct border rendering we must ensure that the distance between
+ // two cells is exactly 2 * td->border pixel. we do this by rounding the calculated width
+ // values here.
+ // to minimize the total rounding error we propagate the rounding error for each width
+ // to its successor.
+ QFixed error = 0;
+ for (int i = 0; i < columns; ++i) {
+ QFixed orig = td->widths[i];
+ td->widths[i] = (td->widths[i] - error).round();
+ error = td->widths[i] - orig;
+ }
+
td->columnPositions.resize(columns);
td->columnPositions[0] = leftMargin /*includes table border*/ + cellSpacing + td->border;
@@ -1887,7 +1903,7 @@ relayout:
if (cellRow != r) {
// the last row gets all the remaining space
if (cellRow + rspan - 1 == r)
- td->heights[r] = qMax(td->heights.at(r), heightToDistribute.at(c) - dropDistance);
+ td->heights[r] = qMax(td->heights.at(r), heightToDistribute.at(c) - dropDistance).round();
continue;
}
}
@@ -1908,7 +1924,7 @@ relayout:
td, absoluteTableY,
/*withPageBreaks =*/true);
- const QFixed height = layoutStruct.y + bottomPadding + topPadding;
+ const QFixed height = (layoutStruct.y + bottomPadding + topPadding).round();
if (rspan > 1)
heightToDistribute[c] = height + dropDistance;