app/renderer/canvas.js

@@ -109,14 +109,16 @@ class AnnotationCanvas {
   // ---- coordinate helpers ----
   // The focused-view crop region, in coordinates normalized to the full
   // image (0..1). Identity rect when focused view is off, matching
-  // core/raster.js applyFocusedView.
+  // core/raster.js applyFocusedView. panX/panY are 0..1 fractions of the
+  // available pan range (0 = left/bottom edge, 1 = right/top edge), so the
+  // slider's full range always pans the crop across the whole image
+  // regardless of zoom. Y is inverted so panY increases upward.
   viewRect() {
     const fv = this.focusedView;
     if (!fv || !fv.enabled || !(fv.zoom > 1)) return { x: 0, y: 0, w: 1, h: 1 };
     const w = 1 / fv.zoom, h = 1 / fv.zoom;
-    const cx = Math.min(Math.max(fv.panX ?? 0.5, w / 2), 1 - w / 2);
-    const cy = Math.min(Math.max(fv.panY ?? 0.5, h / 2), 1 - h / 2);
-    return { x: cx - w / 2, y: cy - h / 2, w, h };
+    const panX = fv.panX ?? 0.5, panY = fv.panY ?? 0.5;
+    return { x: panX * (1 - w), y: (1 - panY) * (1 - h), w, h };
   }
 
   toNorm(e) {

core/raster.js

@@ -392,13 +392,19 @@ function renderAnnotations(baseImg, annotations = []) {
   return img;
 }
 
-/** Apply focused view (zoom/pan crop, then scale back to original size). */
+/**
+ * Apply focused view (zoom/pan crop, then scale back to original size).
+ * panX/panY are 0..1 fractions of the available pan range, not absolute
+ * image positions: 0 puts the crop at the left/bottom edge, 1 at the
+ * right/top edge, 0.5 centers it. Y is inverted so panY increases upward.
+ */
 function applyFocusedView(img, fv) {
   if (!fv || !fv.enabled || !(fv.zoom > 1)) return img;
   const vw = img.width / fv.zoom, vh = img.height / fv.zoom;
-  const cx = Math.min(Math.max(fv.panX * img.width, vw / 2), img.width - vw / 2);
-  const cy = Math.min(Math.max(fv.panY * img.height, vh / 2), img.height - vh / 2);
-  const region = crop(img, cx - vw / 2, cy - vh / 2, vw, vh);
+  const panX = fv.panX ?? 0.5, panY = fv.panY ?? 0.5;
+  const cropX = panX * (img.width - vw);
+  const cropY = (1 - panY) * (img.height - vh);
+  const region = crop(img, cropX, cropY, vw, vh);
   return resize(region, img.width, img.height);
 }