Export JPEG: a zoomable full-size preview, its buttons and the View menu's zoom keys (13.4b)

src/UI/JPEGExportSheet.h

@@ -1,7 +1,9 @@
 #pragma once
 #include "Document/ColorPalette.h"
 #include "IO/ImageExporter.h"
+#include <QAbstractScrollArea>
 #include <QWidget>
+#include <array>
 #include <atomic>
 #include <functional>
 #include <memory>
@@ -9,12 +11,58 @@
 
 class QLabel;
 class QProgressBar;
+class QShortcut;
 class QPushButton;
 class QSlider;
 class QTimer;
 class DialogColorSwatch;
 class EditorSession;
 
+// Swift's JPEGPreview: the encoded JPEG, fitted or zoomed, dragged.
+class JPEGPreview : public QAbstractScrollArea {
+    Q_OBJECT
+public:
+    static constexpr QSize frame{560, 330};
+    static constexpr std::array<double, 6> steps{0.25, 0.5, 1, 2, 4, 8};
+    // The zoom at which the whole image fits `frame`.
+    static double fitZoom(int width, int height, QSizeF frame, double displayScale);
+    // The next step past `zoom`: 1 in, −1 out.
+    static std::optional<double> step(double zoom, int direction);
+
+    // `pixels`: the export's size, which the image may undercut.
+    JPEGPreview(QSize pixels, std::function<void()> zoomChanged, QWidget *parent);
+    void setImage(const QImage &image, bool updating);
+    // None fits; 1 is a screen pixel a pixel.
+    std::optional<double> zoom() const { return m_zoom; }
+    void setZoom(std::optional<double> zoom);
+    double shownZoom() const;
+    void zoomBy(int direction);
+
+protected:
+    void paintEvent(QPaintEvent *event) override;
+    void resizeEvent(QResizeEvent *event) override;
+    void mousePressEvent(QMouseEvent *event) override;
+    void mouseMoveEvent(QMouseEvent *event) override;
+    void mouseReleaseEvent(QMouseEvent *event) override;
+    void mouseDoubleClickEvent(QMouseEvent *event) override;
+
+private:
+    QSizeF shownSize(double zoom) const;
+    void updateRanges();
+    void showCursor(bool grabbing);
+
+    const QSize m_pixels;
+    // Each change of zoom, for the sheet's buttons.
+    const std::function<void()> m_zoomChanged;
+    QImage m_image;
+    // The image shrunk to the size last drawn.
+    QImage m_reduced;
+    bool m_updating = false;
+    std::optional<double> m_zoom;
+    // A drag's press and the scroll it began from.
+    std::optional<std::pair<QPoint, QPoint>> m_drag;
+};
+
 // Swift's JPEGExportSheet: quality, matte and the encoded preview.
 class JPEGExportSheet : public QWidget {
     Q_OBJECT
@@ -25,12 +73,17 @@ public:
     JPEGExportSheet(ExportRaster raster, EditorSession &session, std::function<void(std::optional<QByteArray>)> finish, QWidget *parent = nullptr);
     ~JPEGExportSheet() override;
 
+protected:
+    // The zoom glyphs follow the theme.
+    void changeEvent(QEvent *event) override;
+
 private:
-    class Preview;
     void request();
     void encode();
     void setMatte(const PaletteColor &matte);
     void synchronize();
+    // The View menu's zoom keys, as remapped, zoom the preview.
+    void bindZoomKeys();
 
     const ExportRaster m_raster;
     EditorSession &m_session;
@@ -42,7 +95,7 @@ private:
     // The newest request's flag, Swift's task cancellation.
     std::shared_ptr<std::atomic_bool> m_cancelled;
     QTimer *const m_wait;
-    Preview *const m_preview;
+    JPEGPreview *const m_preview;
     QProgressBar *const m_spinner;
     QSlider *const m_quality;
     QLabel *const m_percent;
@@ -51,4 +104,9 @@ private:
     QLabel *const m_bytes;
     QLabel *const m_note;
     QPushButton *const m_export;
+    QPushButton *const m_fit;
+    QPushButton *const m_zoomIn;
+    QPushButton *const m_zoomOut;
+    // Fit, Actual Pixels, Zoom In and Zoom Out.
+    std::array<QShortcut *, 4> m_zoomKeys{};
 };