statistics: don't place labels at half-integer values

Placing labels at half-integer values gives horrible
rendering artifacts. Therefore, always round to integer
values. The easiest way to do this is right before setting
the position. Introduce a helper function to round QPointF
in such scenarios.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

Subsurface-mobile.pro

@@ -143,6 +143,7 @@ SOURCES += subsurface-mobile-main.cpp \
 	stats/statsaxis.cpp \
 	stats/statscolors.cpp \
 	stats/statsgrid.cpp \
+	stats/statshelper.cpp \
 	stats/statsseries.cpp \
 	stats/statsstate.cpp \
 	mobile-widgets/qmlinterface.cpp \
@@ -295,6 +296,7 @@ HEADERS += \
 	stats/statsaxis.h \
 	stats/statscolors.h \
 	stats/statsgrid.h \
+	stats/statshelper.h \
 	stats/statsseries.h \
 	stats/statsstate.h \
 	stats/statstranslations.h \

stats/CMakeLists.txt

@@ -34,6 +34,8 @@ set(SUBSURFACE_STATS_SRCS
 	statscolors.cpp
 	statsgrid.h
 	statsgrid.cpp
+	statshelper.h
+	statshelper.cpp
 	statsseries.h
 	statsseries.cpp
 	statsstate.h

stats/barseries.cpp

@@ -118,7 +118,7 @@ void BarSeries::BarLabel::updatePosition(bool horizontal, bool center, const QRe
 			return;
 		}
 		QPointF pos = rect.center();
-		pos.rx() -= round(itemSize.width() / 2.0);
+		pos.rx() -= itemSize.width() / 2.0;
 
 		// Heuristics: if the label fits nicely into the bar (bar height is at least twice the label height),
 		// then put the label in the middle of the bar. Otherwise, put it at the top of the bar.
@@ -130,29 +130,29 @@ void BarSeries::BarLabel::updatePosition(bool horizontal, bool center, const QRe
 				setVisible(false);
 				return;
 			}
-			pos.ry() -= round(itemSize.height() / 2.0);
+			pos.ry() -= itemSize.height() / 2.0;
 		}
-		item->setPos(pos);
+		item->setPos(roundPos(pos)); // Round to integer to avoid ugly artifacts.
 	} else {
 		if (itemSize.height() > rect.height()) {
 			setVisible(false);
 			return;
 		}
 		QPointF pos = rect.center();
-		pos.ry() -= round(itemSize.height() / 2.0);
+		pos.ry() -= itemSize.height() / 2.0;
 
 		// Heuristics: if the label fits nicely into the bar (bar width is at least twice the label height),
 		// then put the label in the middle of the bar. Otherwise, put it to the right of the bar.
 		isOutside = !center && rect.width() < 2.0 * itemSize.width();
 		if (isOutside) {
-			pos.rx() = round(rect.right() + 2.0); // Leave two pixels(?) space
+			pos.rx() = rect.right() + 2.0; // Leave two pixels(?) space
 		} else {
 			if (itemSize.width() > rect.width()) {
 				setVisible(false);
 				return;
 			}
 		}
-		item->setPos(pos);
+		item->setPos(roundPos(pos)); // Round to integer to avoid ugly artifacts.
 	}
 	setVisible(true);
 	// If label changed from inside to outside, or vice-versa, the color might change.

stats/pieseries.cpp

@@ -44,8 +44,9 @@ void PieSeries::Item::updatePositions(const QPointF &center, double radius)
 	// because half-integer values gives horrible aliasing artifacts.
 	if (innerLabel) {
 		QRectF labelRect = innerLabel->getRect();
-		innerLabel->setPos(QPointF(round(center.x() + innerLabelPos.x() * radius - labelRect.width() / 2.0),
-					   round(center.y() + innerLabelPos.y() * radius - labelRect.height() / 2.0)));
+		QPointF pos(center.x() + innerLabelPos.x() * radius - labelRect.width() / 2.0,
+			    center.y() + innerLabelPos.y() * radius - labelRect.height() / 2.0);
+		innerLabel->setPos(roundPos(pos));
 	}
 	if (outerLabel) {
 		QRectF labelRect = outerLabel->getRect();
@@ -59,7 +60,7 @@ void PieSeries::Item::updatePositions(const QPointF &center, double radius)
 			pos.ry() -= labelRect.height();
 		}
 
-		outerLabel->setPos(QPointF(round(pos.x()), round(pos.y())));
+		outerLabel->setPos(roundPos(pos));
 	}
 }
 

stats/statshelper.cpp

@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "statshelper.h"
+
+#include <cmath>
+
+QPointF roundPos(const QPointF &p)
+{
+	return QPointF(round(p.x()), round(p.y()));
+}

stats/statshelper.h

@@ -1,12 +1,16 @@
 // SPDX-License-Identifier: GPL-2.0
-// Helper functions to render the stats. Currently contains
+// Helper functions to render the stats. Includes
 // QSGNode template jugglery to overcome API flaws.
 #ifndef STATSHELPER_H
 #define STATSHELPER_H
 
 #include <memory>
+#include <QPointF>
 #include <QSGNode>
 
+// Round positions to integer values to avoid ugly artifacts
+QPointF roundPos(const QPointF &p);
+
 // A stupid pointer class that initializes to null and can be copy
 // assigned. This is for historical reasons: unique_ptrs to ChartItems
 // were replaced by plain pointers. Instead of nulling the plain pointers

stats/statsview.cpp

@@ -397,8 +397,8 @@ void StatsView::updateTitlePos()
 {
 	if (!title)
 		return;
-	title->setPos(QPointF(round(sceneBorder + (boundingRect().width() - title->getRect().width()) / 2.0),
-			      round(sceneBorder)));
+	QPointF pos(sceneBorder + (boundingRect().width() - title->getRect().width()) / 2.0, sceneBorder);
+	title->setPos(roundPos(pos));
 }
 
 template <typename T, class... Args>