14.20: the Navigator minimap from 300%

src/UI/NavigatorMinimap.h

@@ -0,0 +1,50 @@
+#pragma once
+#include "Document/EditorSession.h"
+#include <QTimer>
+#include <QWidget>
+
+// Swift's NavigatorMinimap: the document in small, from 300%.
+class NavigatorMinimap : public QWidget {
+    Q_OBJECT
+public:
+    static constexpr double zoomShown = 3;
+    // The most room the document takes, in points.
+    static constexpr QSizeF largest{126, 90};
+    // Pixels on the picture's longer side.
+    static constexpr int picturePixels = 300;
+    // Swift's AppStorage key; off until View › Navigator.
+    static constexpr const char *visibleKey = "navigator.visible";
+    static bool visibleSetting();
+    static void setVisibleSetting(bool visible);
+    // Fitted inside `largest`, its proportions kept, rounded.
+    static QSizeF sizeFor(QSizeF document);
+
+    // What the picture comes from: layers, not the selection.
+    struct RenderKey {
+        QUuid documentID;
+        QSizeF size;
+        std::vector<ImageLayer> layers;
+        int revision = 0;
+        RenderKey(const std::optional<CanvasDocument> &document, int revision);
+        friend bool operator==(const RenderKey &, const RenderKey &) = default;
+    };
+
+    explicit NavigatorMinimap(EditorSession &session, QWidget *parent = nullptr);
+    void synchronize();
+    const QImage &picture() const { return m_picture; }
+
+protected:
+    void paintEvent(QPaintEvent *event) override;
+    void mousePressEvent(QMouseEvent *event) override;
+    void mouseMoveEvent(QMouseEvent *event) override;
+
+private:
+    void render();
+    void centre(QPointF point);
+
+    EditorSession &m_session;
+    QImage m_picture;
+    std::optional<RenderKey> m_key;
+    // Edits settle first: the picture redraws once, afterwards.
+    QTimer *const m_wait;
+};