Set draw layer offset and init scale

src/app/application.js

@@ -1891,7 +1891,7 @@ export class App {
     // sync layer groups
     this.#stage.fitToContainer();
 
-    // view layer offset (done before scale)
+    // layer offset (done before scale)
     viewLayer.setOffset(layerGroup.getOffset());
 
     // get and apply flip flags
@@ -2006,13 +2006,28 @@ export class App {
     // sync layer groups
     this.#stage.fitToContainer();
 
+    // layer offset (done before scale)
+    drawLayer.setOffset(layerGroup.getOffset());
+
     // get and apply flip flags
     const flipFlags = this.#getViewFlipFlags(
       imageGeometry.getOrientation(),
       viewConfig.orientation);
     this.#applyFlipFlags(flipFlags, drawLayer);
 
-    drawLayer.setScale(layerGroup.getScale());
+    // do we have more than one layer
+    const noViewLayers = layerGroup.getNumberOfViewLayers() === 0;
+    // layer scale (done after possible flip)
+    if (!noViewLayers) {
+      // use zoom offset of base layer
+      const baseViewLayer = layerGroup.getBaseViewLayer();
+      drawLayer.initScale(
+        layerGroup.getScale(),
+        baseViewLayer.getAbsoluteZoomOffset()
+      );
+    } else {
+      drawLayer.setScale(layerGroup.getScale());
+    }
 
     // add possible existing data
     drawLayer.setAnnotationGroup(

src/gui/drawLayer.js

@@ -394,6 +394,36 @@ export class DrawLayer {
     this.#updateLabelScale(finalNewScale);
   }
 
+  /**
+   * Initialise the layer scale.
+   *
+   * @param {Scalar3D} newScale The scale as {x,y,z}.
+   * @param {Scalar2D} absoluteZoomOffset The zoom offset as {x,y}
+   *   without the fit scale (as provided by getAbsoluteZoomOffset).
+   */
+  initScale(newScale, absoluteZoomOffset) {
+    const orientedNewScale = this.#planeHelper.getTargetOrientedPositiveXYZ({
+      x: newScale.x * this.#flipScale.x,
+      y: newScale.y * this.#flipScale.y,
+      z: newScale.z * this.#flipScale.z,
+    });
+    const finalNewScale = {
+      x: this.#fitScale.x * orientedNewScale.x,
+      y: this.#fitScale.y * orientedNewScale.y
+    };
+    this.#konvaStage.scale(finalNewScale);
+
+    this.#zoomOffset = {
+      x: absoluteZoomOffset.x / this.#fitScale.x,
+      y: absoluteZoomOffset.y / this.#fitScale.y
+    };
+    const offset = this.#konvaStage.offset();
+    this.#konvaStage.offset({
+      x: offset.x + this.#zoomOffset.x,
+      y: offset.y + this.#zoomOffset.y
+    });
+  }
+
   /**
    * Set the layer offset.
    *