Improve drag-and-drop in SenderPdfImageEditor

Replaced the old drag-and-drop implementation with a custom solution using mouse events for better control and precision. Added `_isDragging` state and dynamic cursor updates to enhance user feedback during drag operations.

Introduced grab offset calculations to ensure accurate field positioning relative to the pointer. Added `OnEditorMouseUp` to reset the drag state and `GetPageSize` to retrieve page dimensions, defaulting to A4 if unavailable.

Updated `envelope-editor.js` to include `pageNumber` in `getClickCoordsOnPdfPage` and removed the obsolete `getDropCoordsOnPage` function. Enhanced `EditorCoords` to include `PageNumber` for improved page identification.

EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Components/PdfEditor/SenderPdfImageEditor.razor

@@ -5,8 +5,11 @@
 @inject IJSRuntime JSRuntime
 
 <div class="pdf-editor-wrapper sender-image-editor sender-editor-pdf-viewer"
-     style="cursor: @(IsPlacementMode ? "crosshair" : "default");"
+     style="cursor: @(IsPlacementMode ? "crosshair" : (_isDragging ? "grabbing" : "default"));"
-     @onclick="HandleClickAsync">
+     @onclick="HandleClickAsync"
+     @onmousemove="OnEditorMouseMoveAsync"
+     @onmouseup="OnEditorMouseUp"
+     @onmouseleave="OnEditorMouseUp">
 @if (PageCount <= 0)
     {
         <div class="sender-image-editor__empty">@L("SenderEditor_NoPagesToDisplay", "Keine Seiten zur Anzeige verfügbar.")</div>
@@ -36,11 +39,7 @@
                      data-page-height-pt="@heightPt">
                     <div class="sender-image-editor__page-canvas"
                          data-editor-page-canvas="@pageNumber"
-                         ondragover="event.preventDefault(); if (event.dataTransfer) event.dataTransfer.dropEffect = 'move';"
+                         style="@( _isDragging ? "cursor:grabbing;" : string.Empty)">
-                         ondragenter="event.preventDefault();"
-                         @ondrop:preventDefault="true"
-                         @ondrop:stopPropagation="true"
-                         @ondrop="args => OnPageDropAsync(args, pageNumber, widthPt, heightPt)">
                         @if (!string.IsNullOrWhiteSpace(pagePreview?.ImageDataUrl))
                         {
                             <img class="sender-image-editor__page-image"
@@ -58,9 +57,8 @@
                             <div class="sender-image-editor__field"
                                  style="@GetFieldStyle(field, widthPt, heightPt)"
                                  title="@field.ReceiverName"
-                                 draggable="true"
+                                 @onmousedown="args => OnFieldMouseDownAsync(args, field)"
-                                 @onmousedown="() => OnFieldDragStart(field.Index)"
+                                 @onmousedown:preventDefault="true"
-                                 ondragstart="event.dataTransfer.setData('text/plain', 'field'); event.dataTransfer.effectAllowed = 'move';"
                                  @onclick:stopPropagation="true">
                                 <span class="sender-image-editor__field-label">@field.ReceiverName</span>
                                 <button type="button"
@@ -108,6 +106,9 @@
     public EventCallback<SenderPdfFieldMoveRequest> MoveField { get; set; }
 
     private int? _draggedFieldIndex;
+    private bool _isDragging;
+    private double _grabOffsetXPt;
+    private double _grabOffsetYPt;
 
     private static string GetFieldStyle(SenderPdfFieldOverlay field, double pageWidthPt, double pageHeightPt)
     {
@@ -131,39 +132,69 @@
             await EditorClick.InvokeAsync(args);
     }
 
-    private void OnFieldDragStart(int fieldIndex)
+    private async Task OnFieldMouseDownAsync(MouseEventArgs args, SenderPdfFieldOverlay field)
     {
-        _draggedFieldIndex = fieldIndex;
+        var coords = await JSRuntime.InvokeAsync<EditorCoords?>(
-    }
+            "envelopeEditor.getClickCoordsOnPdfPage",
-
-    private async Task OnPageDropAsync(DragEventArgs args, int pageNumber, double pageWidthPt, double pageHeightPt)
-    {
-        if (_draggedFieldIndex is null || !MoveField.HasDelegate)
-            return;
-
-        var coords = await JSRuntime.InvokeAsync<DropCoords?>(
-            "envelopeEditor.getDropCoordsOnPage",
             "sender-editor-pdf-viewer",
-            pageNumber,
             args.ClientX,
             args.ClientY);
 
         if (coords is null)
             return;
 
+        var pageNumber = coords.PageNumber;
+        var (pageWidthPt, pageHeightPt) = GetPageSize(pageNumber);
+        var pointerXPt = coords.NormX * pageWidthPt;
+        var pointerYPt = coords.NormY * pageHeightPt;
+
+        _draggedFieldIndex = field.Index;
+        _isDragging = true;
+        _grabOffsetXPt = pointerXPt - field.XPt;
+        _grabOffsetYPt = pointerYPt - field.YPt;
+    }
+
+    private async Task OnEditorMouseMoveAsync(MouseEventArgs args)
+    {
+        if (_draggedFieldIndex is null || !MoveField.HasDelegate)
+            return;
+
+        var coords = await JSRuntime.InvokeAsync<EditorCoords?>(
+            "envelopeEditor.getClickCoordsOnPdfPage",
+            "sender-editor-pdf-viewer",
+            args.ClientX,
+            args.ClientY);
+
+        if (coords is null)
+            return;
+
+        var pageNumber = coords.PageNumber;
+        var (pageWidthPt, pageHeightPt) = GetPageSize(pageNumber);
+
         const double sigWidthPt = 1.77 * 72;
         const double sigHeightPt = 1.96 * 72;
 
-        var xPt = coords.NormX * pageWidthPt;
+        var xPt = (coords.NormX * pageWidthPt) - _grabOffsetXPt;
-        var yPt = coords.NormY * pageHeightPt;
+        var yPt = (coords.NormY * pageHeightPt) - _grabOffsetYPt;
         xPt = Math.Max(0, Math.Min(xPt, pageWidthPt - sigWidthPt));
         yPt = Math.Max(0, Math.Min(yPt, pageHeightPt - sigHeightPt));
 
         await MoveField.InvokeAsync(new SenderPdfFieldMoveRequest(_draggedFieldIndex.Value, pageNumber, xPt, yPt));
-        _draggedFieldIndex = null;
     }
 
-    private sealed record DropCoords(double NormX, double NormY);
+    private void OnEditorMouseUp(MouseEventArgs _)
+    {
+        _draggedFieldIndex = null;
+        _isDragging = false;
+    }
+
+    private (double WidthPt, double HeightPt) GetPageSize(int pageNumber)
+    {
+        var page = Pages.FirstOrDefault(p => p.PageNumber == pageNumber);
+        return page is null ? (595.0, 842.0) : (page.WidthPt, page.HeightPt);
+    }
+
+    private sealed record EditorCoords(double NormX, double NormY, int PageIndex, int PageNumber);
 
     private string L(string key, string fallback)
     {

EnvelopeGenerator.Server/EnvelopeGenerator.Server/wwwroot/js/envelope-editor.js

@@ -90,33 +90,8 @@ window.envelopeEditor = {
         return {
             normX:     normX,
             normY:     normY,
-            pageIndex: targetIndex
+            pageIndex: targetIndex,
-        };
+            pageNumber: parseInt(targetPage.getAttribute('data-editor-page') || String(targetIndex + 1), 10)
-    },
-
-    getDropCoordsOnPage: function (viewerCssClass, pageNumber, clientX, clientY) {
-        const viewer = document.querySelector('.' + viewerCssClass);
-        if (!viewer) {
-            console.warn('[envelopeEditor] viewer not found for class:', viewerCssClass);
-            return null;
-        }
-
-        const page = viewer.querySelector('[data-editor-page="' + pageNumber + '"]');
-        if (!page) {
-            console.warn('[envelopeEditor] page not found:', pageNumber);
-            return null;
-        }
-
-        const rect = page.getBoundingClientRect();
-        const clampedX = Math.max(rect.left, Math.min(clientX, rect.right));
-        const clampedY = Math.max(rect.top, Math.min(clientY, rect.bottom));
-
-        const normX = (clampedX - rect.left) / rect.width;
-        const normY = (clampedY - rect.top) / rect.height;
-
-        return {
-            normX: normX,
-            normY: normY
         };
     }
 };