14.18 round 1: a starved PDF throws, an early zoom centres, inches round to even, tests tightened

src/IO/ImageExporter.cpp

@@ -258,7 +258,11 @@ try {
     content += pageWidth + " 0 0 " + pageHeight + " 0 0 cm /Im0 Do\nQ";
     // zlib's stream, without Qt's four-byte length.
     const auto stream = [](const QByteArray &dictionary, const QByteArray &bytes, bool deflate) {
-        const QByteArray body = deflate ? qCompress(bytes, 9).mid(4) : bytes;
+        const QByteArray compressed = deflate ? qCompress(bytes, 9) : QByteArray();
+        // qCompress says no memory with an empty array.
+        if (deflate && compressed.isEmpty())
+            throw ExportError(ExportError::Kind::render);
+        const QByteArray body = deflate ? compressed.mid(4) : bytes;
         return "<< " + dictionary + (deflate ? " /Filter /FlateDecode" : "") + " /Length " + QByteArray::number(body.size()) + " >>\nstream\n" + body
             + "\nendstream";
     };

src/UI/ExportAsSheet+Preview.cpp

@@ -51,8 +51,12 @@ void JPEGPreview::setImage(const QImage &image, QSize pixels, bool updating)
     m_image = image;
     m_updating = updating;
     if (pixels != m_pixels) {
+        // Swift's onAppear: a zoom set before the first image centres.
+        const bool first = m_pixels.isEmpty();
         m_pixels = pixels;
         updateRanges();
+        if (first && m_zoom)
+            scrollTo(QPointF(0.5, 0.5));
     }
     viewport()->update();
 }
@@ -82,20 +86,25 @@ void JPEGPreview::setZoom(std::optional<double> zoom)
     }
     m_zoom = zoom;
     updateRanges();
-    if (m_zoom) {
-        const QSizeF size = shownSize(*m_zoom);
-        const QSizeF shown(viewport()->size());
-        const double x = std::clamp(fraction.x() * size.width() - shown.width() / 2, 0.0, std::max(0.0, size.width() - shown.width()));
-        const double y = std::clamp(fraction.y() * size.height() - shown.height() / 2, 0.0, std::max(0.0, size.height() - shown.height()));
-        horizontalScrollBar()->setValue(int(std::lround(x)));
-        verticalScrollBar()->setValue(int(std::lround(y)));
-    }
+    if (m_zoom)
+        scrollTo(fraction);
     m_drag.reset();
     showCursor(false);
     viewport()->update();
     m_zoomChanged();
 }
 
+// Puts `fraction` of the image in the view's middle.
+void JPEGPreview::scrollTo(QPointF fraction)
+{
+    const QSizeF size = shownSize(m_zoom.value());
+    const QSizeF shown(viewport()->size());
+    const double x = std::clamp(fraction.x() * size.width() - shown.width() / 2, 0.0, std::max(0.0, size.width() - shown.width()));
+    const double y = std::clamp(fraction.y() * size.height() - shown.height() / 2, 0.0, std::max(0.0, size.height() - shown.height()));
+    horizontalScrollBar()->setValue(int(std::lround(x)));
+    verticalScrollBar()->setValue(int(std::lround(y)));
+}
+
 // The image's size on screen at `zoom`, in points.
 QSizeF JPEGPreview::shownSize(double zoom) const
 {

src/UI/ExportAsSheet.cpp

@@ -47,10 +47,18 @@ double startQuality()
     return number && std::isfinite(saved) ? std::clamp(saved, 0.0, 1.0) : JPEGOptions().quality;
 }
 
-// Swift's 0...2 decimals, trailing zeros dropped.
+// Swift's 0...2 decimals: its shortest digits, halves to even.
 QString inches(double value)
 {
-    QString shown = QLocale(QLocale::English, QLocale::UnitedStates).toString(value, 'f', 2);
+    const QString digits = QString::number(value, 'f', QLocale::FloatingPointShortest);
+    const qsizetype point = digits.indexOf(QLatin1Char('.'));
+    const QString fraction = point < 0 ? QString() : digits.mid(point + 1);
+    qint64 hundredths = digits.left(point < 0 ? digits.size() : point).toLongLong() * 100 + fraction.left(2).leftJustified(2, QLatin1Char('0')).toLongLong();
+    const QString rest = fraction.mid(2);
+    const int half = rest.isEmpty() ? -1 : QString(rest).compare(QStringLiteral("5").leftJustified(rest.size(), QLatin1Char('0')));
+    if (half > 0 || (half == 0 && hundredths % 2 == 1))
+        ++hundredths;
+    QString shown = QLocale(QLocale::English, QLocale::UnitedStates).toString(hundredths / 100.0, 'f', 2);
     while (shown.contains(QLatin1Char('.')) && (shown.endsWith(QLatin1Char('0')) || shown.endsWith(QLatin1Char('.'))))
         shown.chop(1);
     return shown;

src/UI/ExportAsSheet.h

@@ -54,6 +54,7 @@ protected:
 private:
     static QPixmap checkerboard(double ratio);
     QSizeF shownSize(double zoom) const;
+    void scrollTo(QPointF fraction);
     void updateRanges();
     void showCursor(bool grabbing);