3 files changed, 163 insertions, 0 deletions
diff --git a/stats/CMakeLists.txt b/stats/CMakeLists.txt
index e4c110271..11b091d1b 100644
--- a/stats/CMakeLists.txt
+++ b/stats/CMakeLists.txt
@@ -5,6 +5,8 @@ include_directories(.
 )
 
 set(SUBSURFACE_STATS_SRCS
+	legend.h
+	legend.cpp
 	statscolors.h
 	statscolors.cpp
 	statsvariables.h
diff --git a/stats/legend.cpp b/stats/legend.cpp
new file mode 100644
index 000000000..b532f483f
--- /dev/null
+++ b/stats/legend.cpp
@@ -0,0 +1,125 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "legend.h"
+#include "statscolors.h"
+#include <QFontMetrics>
+#include <QGraphicsSceneMouseEvent>
+#include <QGraphicsWidget>
+#include <QPen>
+
+static const double legendBorderSize = 2.0;
+static const double legendBoxBorderSize = 1.0;
+static const double legendBoxScale = 0.8;		// 1.0: text-height of the used font
+static const double legendInternalBorderSize = 2.0;
+static const QColor legendColor(0x00, 0x8e, 0xcc, 192); // Note: fourth argument is opacity
+static const QColor legendBorderColor(Qt::black);
+
+Legend::Legend(QGraphicsWidget *chart, const std::vector<QString> &names) :
+	QGraphicsRectItem(chart), chart(chart), displayedItems(0), width(0.0), height(0.0)
+{
+	setZValue(30.0); // On top of everything else.
+	entries.reserve(names.size());
+	int idx = 0;
+	for (const QString &name: names)
+		entries.emplace_back(name, idx++, (int)names.size(), this);
+
+	// Calculate the height and width of the elements
+	if (!entries.empty()) {
+		QFontMetrics fm(entries[0].text->font());
+		fontHeight = fm.height();
+		for (Entry &e: entries)
+			e.width = fontHeight + 2.0 * legendBoxBorderSize +
+				  fm.size(Qt::TextSingleLine, e.text->text()).width();
+	} else {
+		fontHeight = 0.0;
+	}
+	setPen(QPen(legendBorderColor, legendBorderSize));
+	setBrush(QBrush(legendColor));
+
+	resize(); // Draw initial legend
+}
+
+Legend::Entry::Entry(const QString &name, int idx, int numBins, QGraphicsItem *parent) :
+	rect(new QGraphicsRectItem(parent)),
+	text(new QGraphicsSimpleTextItem(name, parent))
+{
+	rect->setZValue(30.0);
+	rect->setPen(QPen(legendBorderColor, legendBoxBorderSize));
+	rect->setBrush(QBrush(binColor(idx, numBins)));
+	text->setZValue(30.0);
+	text->setBrush(QBrush(darkLabelColor));
+}
+
+void Legend::hide()
+{
+	for (Entry &e: entries) {
+		e.rect->hide();
+		e.text->hide();
+	}
+	QGraphicsRectItem::hide();
+}
+
+void Legend::resize()
+{
+	if (entries.empty())
+		return hide();
+
+	QSizeF size = chart->size();
+
+	// Silly heuristics: make the legend at most half as high and half as wide as the chart.
+	// Not sure if that makes sense - this might need some optimization.
+	int maxRows = static_cast<int>(size.height() / 2.0 - 2.0 * legendInternalBorderSize) / fontHeight;
+	if (maxRows <= 0)
+		return hide();
+	int numColumns = ((int)entries.size() - 1) / maxRows + 1;
+	int numRows = ((int)entries.size() - 1) / numColumns + 1;
+
+	double x = legendInternalBorderSize;
+	displayedItems = 0;
+	for (int col = 0; col < numColumns; ++col) {
+		double y = legendInternalBorderSize;
+		double nextX = x;
+
+		for (int row = 0; row < numRows; ++row) {
+			int idx = col * numRows + row;
+			if (idx >= (int)entries.size())
+				break;
+			entries[idx].pos = QPointF(x, y);
+			nextX = std::max(nextX, x + entries[idx].width);
+			y += fontHeight;
+			++displayedItems;
+		}
+		x += nextX;
+		width = nextX;
+		if (width >= size.width() / 2.0) // More than half the chart-width -> give up
+			break;
+	}
+	width += legendInternalBorderSize;
+	height = 2 * legendInternalBorderSize + numRows * fontHeight;
+	updatePosition();
+}
+
+void Legend::updatePosition()
+{
+	if (displayedItems <= 0)
+		return hide();
+	// For now, place the legend in the top right corner.
+	QPointF pos(chart->size().width() - width - 10.0, 10.0);
+	setRect(QRectF(pos, QSizeF(width, height)));
+	for (int i = 0; i < displayedItems; ++i) {
+		QPointF itemPos = pos + entries[i].pos;
+		QRectF rect(itemPos, QSizeF(fontHeight, fontHeight));
+		// Decrease box size by legendBoxScale factor
+		double delta = fontHeight * (1.0 - legendBoxScale) / 2.0;
+		rect = rect.adjusted(delta, delta, -delta, -delta);
+		entries[i].rect->setRect(rect);
+		itemPos.rx() += fontHeight + 2.0 * legendBoxBorderSize;
+		entries[i].text->setPos(itemPos);
+		entries[i].rect->show();
+		entries[i].text->show();
+	}
+	for (int i = displayedItems; i < (int)entries.size(); ++i) {
+		entries[i].rect->hide();
+		entries[i].text->hide();
+	}
+	show();
+}
diff --git a/stats/legend.h b/stats/legend.h
new file mode 100644
index 000000000..e6c5af1e0
--- /dev/null
+++ b/stats/legend.h
@@ -0,0 +1,36 @@
+// SPDX-License-Identifier: GPL-2.0
+// A legend box, which is shown on the chart.
+#ifndef STATS_LEGEND_H
+#define STATS_LEGEND_H
+
+#include <memory>
+#include <vector>
+#include <QGraphicsRectItem>
+
+class QGraphicsSceneMouseEvent;
+
+class Legend : public QGraphicsRectItem {
+public:
+	Legend(QGraphicsWidget *chart, const std::vector<QString> &names);
+	void hover(QPointF pos);
+	void resize(); // called when the chart size changes.
+private:
+	// Each entry is a text besides a rectangle showing the color
+	struct Entry {
+		std::unique_ptr<QGraphicsRectItem> rect;
+		std::unique_ptr<QGraphicsSimpleTextItem> text;
+		QPointF pos;
+		double width;
+		Entry(const QString &name, int idx, int numBins, QGraphicsItem *parent);
+	};
+	QGraphicsWidget *chart;
+	int displayedItems;
+	double width;
+	double height;
+	int fontHeight;
+	std::vector<Entry> entries;
+	void updatePosition();
+	void hide();
+};
+
+#endif