Add configurable PDF viewer options and improve rendering

Introduced `PdfViewerOptions` class to centralize PDF viewer
settings such as scaling, HiDPI support, zoom transitions,
and rendering delays. Bound these options to `appsettings.json`
for dynamic configuration.

Injected `PdfViewerOptions` into `EnvelopeViewer.razor` and
updated `OnInitializedAsync` to pass settings to JavaScript.
Replaced hardcoded values in `pdf-viewer.js` with configurable
options, improving maintainability and flexibility.

Enhanced rendering logic to respect HiDPI settings, maximum
DPR, and smooth zoom transitions. Improved thumbnail rendering
with configurable delays to optimize performance.

EnvelopeGenerator.ReceiverUI/Options/PdfViewerOptions.cs

@@ -0,0 +1,64 @@
+namespace EnvelopeGenerator.ReceiverUI.Options;
+
+public class PdfViewerOptions
+{
+    public const string SectionName = "PdfViewer";
+
+    /// <summary>
+    /// Base scale for thumbnail rendering (0.2 - 1.5 recommended)
+    /// Higher values = better quality but slower rendering
+    /// Default: 0.75
+    /// </summary>
+    public double ThumbnailBaseScale { get; set; } = 0.75;
+
+    /// <summary>
+    /// Enable HiDPI/Retina support for thumbnails
+    /// Default: true
+    /// </summary>
+    public bool ThumbnailEnableHiDPI { get; set; } = true;
+
+    /// <summary>
+    /// Maximum device pixel ratio multiplier for thumbnails (1.0 - 3.0)
+    /// Caps DPR to avoid excessive memory usage on 4K+ displays
+    /// Default: 2.0
+    /// </summary>
+    public double ThumbnailMaxDPR { get; set; } = 2.0;
+
+    /// <summary>
+    /// Enable HiDPI/Retina support for main PDF canvas
+    /// Default: true
+    /// </summary>
+    public bool MainCanvasEnableHiDPI { get; set; } = true;
+
+    /// <summary>
+    /// Maximum device pixel ratio multiplier for main canvas (1.0 - 3.0)
+    /// Default: 2.0
+    /// </summary>
+    public double MainCanvasMaxDPR { get; set; } = 2.0;
+
+    /// <summary>
+    /// Enable smooth zoom transition (fade effect)
+    /// Default: true
+    /// </summary>
+    public bool EnableSmoothZoom { get; set; } = true;
+
+    /// <summary>
+    /// Zoom transition duration in milliseconds (50 - 500)
+    /// Default: 150
+    /// </summary>
+    public int ZoomTransitionDuration { get; set; } = 150;
+
+    /// <summary>
+    /// Opacity during rendering (0.0 - 1.0)
+    /// Lower values = more visible fade effect
+    /// Default: 0.85
+    /// </summary>
+    public double RenderingOpacity { get; set; } = 0.85;
+
+    /// <summary>
+    /// Delay between thumbnail renders in milliseconds (10 - 200)
+    /// Higher values = less browser stress, slower initial load
+    /// Default: 50
+    /// </summary>
+    public int ThumbnailRenderDelay { get; set; } = 50;
+}

EnvelopeGenerator.ReceiverUI/Pages/EnvelopeViewer.razor

@@ -6,6 +6,7 @@
 @inject DocumentService DocumentService
 @inject NavigationManager Navigation
 @inject IOptions<ApiOptions> AppOptions
+@inject IOptions<PdfViewerOptions> PdfViewerOptions
 @inject IJSRuntime JSRuntime
 @inject AnnotationService AnnotService
 @implements IAsyncDisposable
@@ -236,6 +237,21 @@ protected override async Task OnInitializedAsync() {
             
             try {
                 _dotNetRef = DotNetObjectReference.Create(this);
+                
+                // Send quality options to JavaScript
+                var options = PdfViewerOptions.Value;
+                await JSRuntime.InvokeVoidAsync("pdfViewer.setQualityOptions", new
+                {
+                    options.ThumbnailBaseScale,
+                    options.ThumbnailEnableHiDPI,
+                    options.ThumbnailMaxDPR,
+                    options.MainCanvasEnableHiDPI,
+                    options.MainCanvasMaxDPR,
+                    options.EnableSmoothZoom,
+                    options.ZoomTransitionDuration,
+                    options.RenderingOpacity
+                });
+                
                 var success = await JSRuntime.InvokeAsync<bool>("pdfViewer.initialize", "pdf-canvas", _pdfDataUrl, _dotNetRef);
                 
                 if (success) {
@@ -337,13 +353,15 @@ protected override async Task OnInitializedAsync() {
 
     async Task RenderThumbnailsAsync() {
         try {
+            var delay = PdfViewerOptions.Value.ThumbnailRenderDelay;
+            
             // Sequential rendering to avoid overwhelming the browser
             for (int i = 1; i <= _totalPages; i++) {
                 await JSRuntime.InvokeVoidAsync("pdfViewer.renderThumbnail", i, $"thumb-canvas-{i}");
                 
-                // Small delay between renders to keep UI responsive
+                // Configurable delay between renders
                 if (i < _totalPages) {
-                    await Task.Delay(50);
+                    await Task.Delay(delay);
                 }
             }
         } catch (Exception ex) {

EnvelopeGenerator.ReceiverUI/Program.cs

@@ -14,6 +14,8 @@ builder.RootComponents.Add<HeadOutlet>("head::after");
 builder.Services.AddScoped(sp => new HttpClient { BaseAddress = new Uri(builder.HostEnvironment.BaseAddress) });
 builder.Services.Configure<ApiOptions>(opts =>
 builder.Configuration.GetSection(ApiOptions.SectionName).Bind(opts));
+builder.Services.Configure<PdfViewerOptions>(opts =>
+builder.Configuration.GetSection(PdfViewerOptions.SectionName).Bind(opts));
 builder.Services.AddScoped<EnvelopeGenerator.ReceiverUI.Services.DocumentService>();
 builder.Services.AddScoped<EnvelopeGenerator.ReceiverUI.Services.AuthService>();
 builder.Services.AddScoped<EnvelopeGenerator.ReceiverUI.Services.AnnotationService>();

EnvelopeGenerator.ReceiverUI/wwwroot/appsettings.json

@@ -2,5 +2,16 @@
   "Api": {
     "BaseUrl": "",
     "ForceToUseFakeDocument": false
+  },
+  "PdfViewer": {
+    "ThumbnailBaseScale": 0.75,
+    "ThumbnailEnableHiDPI": true,
+    "ThumbnailMaxDPR": 2.0,
+    "MainCanvasEnableHiDPI": true,
+    "MainCanvasMaxDPR": 2.0,
+    "EnableSmoothZoom": true,
+    "ZoomTransitionDuration": 900,
+    "RenderingOpacity": 0.85,
+    "ThumbnailRenderDelay": 50
   }
 }

EnvelopeGenerator.ReceiverUI/wwwroot/js/pdf-viewer.js

@@ -11,6 +11,27 @@ window.pdfViewer = {
     currentRenderTask: null,
     dotNetReference: null,
     wheelEventAttached: false,
+    
+    // Quality options (configurable from appsettings.json)
+    qualityOptions: {
+        thumbnailBaseScale: 0.75,
+        thumbnailEnableHiDPI: true,
+        thumbnailMaxDPR: 2.0,
+        mainCanvasEnableHiDPI: true,
+        mainCanvasMaxDPR: 2.0,
+        enableSmoothZoom: true,
+        zoomTransitionDuration: 150,
+        renderingOpacity: 0.85
+    },
+
+    setQualityOptions(options) {
+        this.qualityOptions = { ...this.qualityOptions, ...options };
+        console.log('PDF Viewer quality options updated:', this.qualityOptions);
+        
+        // Apply CSS variables for dynamic styling
+        document.documentElement.style.setProperty('--zoom-transition-duration', `${options.zoomTransitionDuration}ms`);
+        document.documentElement.style.setProperty('--rendering-opacity', options.renderingOpacity);
+    },
 
     async initialize(canvasId, pdfDataUrl, dotNetRef) {
         try {
@@ -98,8 +119,10 @@ window.pdfViewer = {
     async renderPage(num) {
         this.pageRendering = true;
         
-        // Add rendering class for smooth transition
+        // Add rendering class for smooth transition (if enabled)
-        this.canvas.classList.add('rendering');
+        if (this.qualityOptions.enableSmoothZoom) {
+            this.canvas.classList.add('rendering');
+        }
 
         try {
             // Get scroll container
@@ -120,9 +143,11 @@ window.pdfViewer = {
 
             const page = await this.pdfDoc.getPage(num);
             
-            // HiDPI support for main canvas
+            // HiDPI support for main canvas (configurable)
-            const dpr = window.devicePixelRatio || 1;
+            const dpr = this.qualityOptions.mainCanvasEnableHiDPI 
-            const viewport = page.getViewport({ scale: this.scale * Math.min(dpr, 2) });
+                ? Math.min(window.devicePixelRatio || 1, this.qualityOptions.mainCanvasMaxDPR)
+                : 1.0;
+            const viewport = page.getViewport({ scale: this.scale * dpr });
 
             // Set internal canvas resolution (high quality)
             this.canvas.width = viewport.width;
@@ -161,7 +186,9 @@ window.pdfViewer = {
             }
 
             // Remove rendering class after completion
-            this.canvas.classList.remove('rendering');
+            if (this.qualityOptions.enableSmoothZoom) {
+                this.canvas.classList.remove('rendering');
+            }
             
             this.currentRenderTask = null;
             this.pageRendering = false;
@@ -275,10 +302,12 @@ window.pdfViewer = {
 
             const page = await this.pdfDoc.getPage(pageNum);
             
-            // High-quality rendering with HiDPI support
+            // High-quality rendering with HiDPI support (configurable)
-            const dpr = window.devicePixelRatio || 1;
+            const dpr = this.qualityOptions.thumbnailEnableHiDPI 
-            const baseScale = 0.75; // Increased base scale for better quality
+                ? Math.min(window.devicePixelRatio || 1, this.qualityOptions.thumbnailMaxDPR)
-            const scale = baseScale * Math.min(dpr, 2); // Cap at 2x for performance
+                : 1.0;
+            const baseScale = this.qualityOptions.thumbnailBaseScale;
+            const scale = baseScale * dpr;
             
             const viewport = page.getViewport({ scale: scale });