jfjoch_viewer: image is auto scaled at the beginning

viewer/image_viewer/JFJochImage.cpp

@@ -7,6 +7,7 @@
 #include <QScrollBar>
 #include <QWheelEvent>
 #include <QMouseEvent>
+#include <QTimer>
 
 JFJochImage::JFJochImage(QWidget *parent) : QGraphicsView(parent) {
     setDragMode(QGraphicsView::NoDrag); // Disable default drag mode
@@ -14,6 +15,8 @@ JFJochImage::JFJochImage(QWidget *parent) : QGraphicsView(parent) {
     setRenderHint(QPainter::Antialiasing); // Enable smooth rendering
     setRenderHint(QPainter::SmoothPixmapTransform);
 
+    setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);
+
     setFocusPolicy(Qt::ClickFocus);
     // Connect the horizontal scrollbar's valueChanged signal
     connect(horizontalScrollBar(), &QScrollBar::valueChanged, this, &JFJochImage::onScroll);
@@ -25,6 +28,16 @@ JFJochImage::JFJochImage(QWidget *parent) : QGraphicsView(parent) {
     color_scale.Select(ColorScaleEnum::Indigo);
 }
 
+void JFJochImage::showEvent(QShowEvent* event) {
+    QGraphicsView::showEvent(event);
+    // Defer fit until after this widget is laid out and has a real viewport size
+    QTimer::singleShot(0, this, [this](){
+        if (!initial_fit_done_) {
+            fitToViewShorterSideOnce();
+        }
+    });
+}
+
 void JFJochImage::onScroll(int value) {
     updateOverlay();
 }
@@ -100,6 +113,9 @@ void JFJochImage::wheelEvent(QWheelEvent *event) {
 
 void JFJochImage::resizeEvent(QResizeEvent *event) {
     QGraphicsView::resizeEvent(event);
+    if (!initial_fit_done_)
+        fitToViewShorterSideOnce();
+
     updateOverlay();
 }
 
@@ -695,36 +711,36 @@ void JFJochImage::CalcROI() {
     }
     emit roiCalculated(msg);
 }
+
 void JFJochImage::fitToViewShorterSideOnce() {
     if (initial_fit_done_)
         return;
     if (W == 0 || H == 0 || !viewport())
         return;
-   // Ensure scene rect matches the image bounds for correct fitting
+
+    // Guard against tiny or zero viewport (happens before layout settles)
+    const QSize vp = viewport()->size();
+    if (vp.width() < 8 || vp.height() < 8) {
+        // remember last tried size; resizeEvent/showEvent will retry
+        last_fit_viewport_ = vp;
+        return;
+    }
+
     if (scene())
         scene()->setSceneRect(QRectF(0, 0, static_cast<qreal>(W), static_cast<qreal>(H)));
 
-    // Temporarily anchor to the view center to avoid drift during fit
     const auto oldAnchor = transformationAnchor();
     setTransformationAnchor(QGraphicsView::AnchorViewCenter);
-
-    // Clear any prior transform before fitting
     setTransform(QTransform());
 
-    // Use Qt's fitter to maximize the image in the viewport with aspect preserved.
-    // This accounts for frame, scrollbars, DPR, and internal rounding.
     fitInView(QRectF(0, 0, static_cast<qreal>(W), static_cast<qreal>(H)), Qt::KeepAspectRatio);
 
-    // Cache the resulting uniform scale
-    scale_factor = transform().m11(); // m11 == m22 for uniform fit
-
-    // Center explicitly (fitInView already centers, but keep it explicit)
+    scale_factor = transform().m11();
     centerOn(QPointF(static_cast<qreal>(W) * 0.5, static_cast<qreal>(H) * 0.5));
-
-    // Restore anchor preference
     setTransformationAnchor(oldAnchor);
 
     initial_fit_done_ = true;
     last_fit_W_ = W;
     last_fit_H_ = H;
+    last_fit_viewport_ = vp;
 }

viewer/image_viewer/JFJochImage.h

@@ -19,6 +19,7 @@ class JFJochImage : public QGraphicsView {
     void writePixelLabels();
     void wheelEvent(QWheelEvent* event) override;
     void resizeEvent(QResizeEvent *event) override;
+    void showEvent(QShowEvent* event) override;
 
     void mousePressEvent(QMouseEvent *event) override;
     void mouseMoveEvent(QMouseEvent *event) override;
@@ -75,6 +76,7 @@ protected:
 
     // Perform initial fit-to-view (shorter direction), once per image size
     void fitToViewShorterSideOnce();
+    QSize last_fit_viewport_ = {};
 signals:
     void foregroundChanged(float v);
     void backgroundChanged(float v);