scene: Render background dynamically

Previously, the scene background was rendered into a pixmap. This had two drawbacks:
  - It uses a lot of memory (and this gets worse quickly when the scene is large).
  - The pre-rendered pixmap was rasterized. Zooming in made the grid appear pixelated.

Fixes #59

qschematic/CMakeLists.txt

@@ -65,6 +65,7 @@ function(setup_target_common target)
                 wire_system/wire.hpp
                 wire_system/point.hpp
                 wire_system/net.hpp
+                background.hpp
                 netlist.hpp
                 netlist_writer_json.hpp
                 netlistgenerator.hpp
@@ -102,6 +103,7 @@ function(setup_target_common target)
             wire_system/wire.cpp
             wire_system/point.cpp
             wire_system/net.cpp
+            background.cpp
             scene.cpp
             settings.cpp
             utils.cpp

qschematic/background.cpp

@@ -0,0 +1,83 @@
+#include "background.hpp"
+
+#include <QPen>
+#include <QBrush>
+#include <QPainter>
+#include <QStyleOptionGraphicsItem>
+
+using namespace QSchematic;
+
+Background::Background(QGraphicsItem* parent) :
+    QGraphicsRectItem(parent)
+{
+    setFlag(QGraphicsItem::ItemUsesExtendedStyleOption, true);  // For QStyleOptionGraphicsItem::exposedRect
+}
+
+void
+Background::setSettings(const Settings& settings)
+{
+    m_settings = settings;
+}
+
+void
+Background::paint(QPainter* painter, const QStyleOptionGraphicsItem* option, QWidget* widget)
+{
+    // ToDo: Use QStyleOptionGraphicsItem::exposedRect
+
+    // Background pen
+    QPen backgroundPen;
+    backgroundPen.setStyle(Qt::NoPen);
+
+    // Background brush
+    QBrush backgroundBrush;
+    backgroundBrush.setStyle(Qt::SolidPattern);
+    backgroundBrush.setColor(Qt::white);
+
+    // Grid pen
+    QPen gridPen;
+    gridPen.setStyle(Qt::SolidLine);
+    gridPen.setColor(Qt::gray);
+    gridPen.setCapStyle(Qt::RoundCap);
+    gridPen.setWidth(m_settings.gridPointSize);
+
+    // Grid brush
+    QBrush gridBrush;
+    gridBrush.setStyle(Qt::NoBrush);
+
+    // Get the rects
+    //
+    // sr = scene rect
+    // ep = exposed rect
+    const QRectF sr = rect();
+    const QRectF er = (option ? option->exposedRect : rect());
+
+    painter->save();
+    painter->setRenderHint(QPainter::Antialiasing, m_settings.antialiasing);
+
+    // Draw background
+    painter->setPen(backgroundPen);
+    painter->setBrush(backgroundBrush);
+    painter->drawRect(rect());
+
+    // Draw the grid if supposed to
+    if (m_settings.showGrid && (m_settings.gridSize > 0)) {
+        qreal left = int(rect().left()) - (int(rect().left()) % m_settings.gridSize);
+        qreal top = int(rect().top()) - (int(rect().top()) % m_settings.gridSize);
+
+        painter->setPen(gridPen);
+        painter->setBrush(gridBrush);
+        for (qreal x = left; x < sr.right(); x += m_settings.gridSize) {
+            for (qreal y = top; y < sr.bottom(); y += m_settings.gridSize)
+                painter->drawPoint(x, y);
+        }
+    }
+
+    // Mark the origin if supposed to
+    if (m_settings.debug) {
+        painter->setPen(Qt::NoPen);
+        painter->setBrush(QBrush(Qt::red));
+        painter->drawEllipse(-6, -6, 12, 12);
+    }
+
+    painter->restore();
+}

qschematic/background.hpp

@@ -0,0 +1,29 @@
+#pragma once
+
+#include "settings.hpp"
+
+#include <QGraphicsRectItem>
+
+namespace QSchematic
+{
+
+    class Background :
+        public QGraphicsRectItem
+    {
+    public:
+        explicit
+        Background(QGraphicsItem* parent = nullptr);
+
+        ~Background() override = default;
+
+        void
+        setSettings(const Settings& settings);
+
+        void
+        paint(QPainter* painter, const QStyleOptionGraphicsItem* option, QWidget* widget) override;
+
+    private:
+        Settings m_settings;
+    };
+
+}

qschematic/scene.cpp

@@ -9,6 +9,7 @@
 #include <QTimer>
 
 #include "scene.hpp"
+#include "background.hpp"
 #include "commands/item_move.hpp"
 #include "commands/item_add.hpp"
 #include "commands/item_remove.hpp"
@@ -54,13 +55,16 @@ Scene::Scene(QObject* parent) :
         _popup->setPos(_lastMousePos + QPointF{ 5, 5 });
     });
 
-    // Stuff
-    connect(this, &QGraphicsScene::sceneRectChanged, [this]{
-        renderCachedBackground();
+    // Background
+    setupBackground();
+    connect(this, &QGraphicsScene::sceneRectChanged, [this](const QRectF rect){
+        if (_background) {
+            // Adjust scene rect (make it smaller) because otherwise the scene resizes automatically to a larger size to accomodate
+            // the background rect and we end up in an infinite loop.
+            // ToDo
+            //_background->setRect(rect.adjusted(10, 10, -10, -10));
+        }
     });
-
-    // Prepare the background
-    renderCachedBackground();
 }
 
 Scene::~Scene()
@@ -170,6 +174,10 @@ Scene::from_container(const gpds::container& container)
 void
 Scene::setSettings(const Settings& settings)
 {
+    // Update background
+    if (_background)
+        _background->setSettings(settings);
+
     // Update settings of all items
     for (auto& item : items())
         item->setSettings(settings);
@@ -181,7 +189,6 @@ Scene::setSettings(const Settings& settings)
     _settings = settings;
 
     // Redraw
-    renderCachedBackground();
     update();
 }
 
@@ -273,8 +280,11 @@ Scene::clear()
     // Now that all the top-level items are safeguarded we can call the underlying scene's clear()
     QGraphicsScene::clear();
 
-    // NO longer dirty
+    // No longer dirty
     clearIsDirty();
+
+    // Setup the background again
+    setupBackground();
 }
 
 bool
@@ -933,14 +943,6 @@ Scene::dropEvent(QGraphicsSceneDragDropEvent* event)
     }
 }
 
-void
-Scene::drawBackground(QPainter* painter, const QRectF& rect)
-{
-    const QPointF& pixmapTopleft = rect.topLeft() - sceneRect().topLeft();
-
-    painter->drawPixmap(rect, _backgroundPixmap, QRectF(pixmapTopleft.x(), pixmapTopleft.y(), rect.width(), rect.height()));
-}
-
 QVector2D
 Scene::itemsMoveSnap(const std::shared_ptr<Items::Item>& items, const QVector2D& moveBy) const
 {
@@ -949,73 +951,14 @@ Scene::itemsMoveSnap(const std::shared_ptr<Items::Item>& items, const QVector2D&
     return moveBy;
 }
 
-QPixmap
-Scene::renderBackground(const QRect& rect) const
-{
-    // Create pixmap
-    QPixmap pixmap(rect.width(), rect.height());
-
-    // Grid pen
-    QPen gridPen;
-    gridPen.setStyle(Qt::SolidLine);
-    gridPen.setColor(Qt::gray);
-    gridPen.setCapStyle(Qt::RoundCap);
-    gridPen.setWidth(_settings.gridPointSize);
-
-    // Grid brush
-    QBrush gridBrush;
-    gridBrush.setStyle(Qt::NoBrush);
-
-    // Create a painter
-    QPainter painter(&pixmap);
-    painter.setRenderHint(QPainter::Antialiasing, _settings.antialiasing);
-
-    // Draw background
-    pixmap.fill(Qt::white);
-
-    // Draw the grid if supposed to
-    if (_settings.showGrid && (_settings.gridSize > 0)) {
-        qreal left = int(rect.left()) - (int(rect.left()) % _settings.gridSize);
-        qreal top = int(rect.top()) - (int(rect.top()) % _settings.gridSize);
-
-        // Create a list of points
-        QVector<QPointF> points;
-        for (qreal x = left; x < rect.right(); x += _settings.gridSize) {
-            for (qreal y = top; y < rect.bottom(); y += _settings.gridSize)
-                points.append(QPointF(x,y));
-        }
-
-        // Draw the actual grid points
-        painter.setPen(gridPen);
-        painter.setBrush(gridBrush);
-        painter.drawPoints(points.data(), points.size());
-    }
-
-    // Mark the origin if supposed to
-    if (_settings.debug) {
-        painter.setPen(Qt::NoPen);
-        painter.setBrush(QBrush(Qt::red));
-        painter.drawEllipse(-6, -6, 12, 12);
-    }
-
-    painter.end();
-
-    return pixmap;
-}
-
 void
-Scene::renderCachedBackground()
+Scene::setupBackground()
 {
-    // Create the pixmap
-    const QRect& rect = sceneRect().toRect();
-    if (rect.isNull() || !rect.isValid())
-        return;
-
-    // Render background
-    _backgroundPixmap = std::move(renderBackground(rect));
-
-    // Update
-    update();
+    _background = new Background(nullptr);
+    _background->setRect(sceneRect());
+    _background->setZValue(z_value_background);
+    _background->setSettings(_settings);
+    QGraphicsScene::addItem(_background);
 }
 
 void

qschematic/scene.hpp

@@ -25,6 +25,8 @@ namespace QSchematic
         class WireNet;
     }
 
+    class Background;
+
     /**
      * The QSchematic Scene.
      *
@@ -41,6 +43,8 @@ namespace QSchematic
     public:
         static constexpr const char* gpds_name = "qschematic";
 
+        qreal z_value_background = -10'000;
+
         enum Mode {
             NormalMode,
             WireMode,
@@ -210,7 +214,6 @@ namespace QSchematic
         void dragMoveEvent(QGraphicsSceneDragDropEvent* event) override;
         void dragLeaveEvent(QGraphicsSceneDragDropEvent* event) override;
         void dropEvent(QGraphicsSceneDragDropEvent* event) override;
-        void drawBackground(QPainter* painter, const QRectF& rect) override;
 
         /**
          * This gets called just before the item is actually being moved by moveBy. Subclasses may
@@ -221,21 +224,11 @@ namespace QSchematic
         QVector2D
         itemsMoveSnap(const std::shared_ptr<Items::Item>& item, const QVector2D& moveBy) const;
 
-        /**
-         * Renders the background.
-         *
-         * @param rect The scene rectangle. This is guaranteed to be non-null & valid.
-         */
-        [[nodiscard]]
-        virtual
-        QPixmap
-        renderBackground(const QRect& rect) const;
-
     private Q_SLOTS:
         void wirePointMoved(wire& rawWire, int index);
 
     private:
-        void renderCachedBackground();
+        void setupBackground();
         void setupNewItem(Items::Item& item);
         void updateNodeConnections(const Items::Node* node);
         void generateConnections();
@@ -272,7 +265,6 @@ namespace QSchematic
         // ItemUtils::ItemsCustodian<Item> _items;
         // ItemUtils::ItemsCustodian<WireNet> m_nets;
 
-        QPixmap _backgroundPixmap;
         std::function<std::shared_ptr<Items::Wire>()> _wireFactory;
         int _mode = NormalMode;
         std::shared_ptr<Items::Wire> _newWire;
@@ -287,6 +279,7 @@ namespace QSchematic
         std::shared_ptr<Items::Item> _highlightedItem = nullptr;
         QTimer* _popupTimer = nullptr;
         std::shared_ptr<QGraphicsProxyWidget> _popup;
+        Background* _background = nullptr;
     };
 
 }