add option to toggle text layer visibility on debug builds

This is to ease debugging text layer on debug builds.

app/src/main/assets/viewer.css

@@ -1,3 +1,8 @@
+:root {
+    --text-layer-opacity: 0.2;
+    --text-layer-foreground: transparent;
+}
+
 html, body {
     height: 100%;
 }
@@ -34,13 +39,13 @@ canvas, .textLayer {
 .textLayer {
     text-align: initial;
     overflow: hidden;
-    opacity: 0.2;
+    opacity: var(--text-layer-opacity);
     line-height: 1;
 }
 
 .textLayer span,
 .textLayer br {
-    color: transparent;
+    color: var(--text-layer-foreground);
     position: absolute;
     white-space: pre;
     cursor: text;

app/src/main/assets/viewer.js

@@ -20,6 +20,8 @@ let useRender;
 const cache = [];
 const maxCached = 6;
 
+let isTextLayerVisible = false;
+
 function maybeRenderNextPage() {
     if (renderPending) {
         pageRendering = false;
@@ -209,6 +211,18 @@ function isTextSelected() {
     return window.getSelection().toString() !== "";
 }
 
+function toggleTextLayerVisibility() {
+    let textLayerForeground = "red";
+    let textLayerOpacity = 1;
+    if (isTextLayerVisible) {
+        textLayerForeground = "transparent";
+        textLayerOpacity = 0.2;
+    }
+    document.documentElement.style.setProperty("--text-layer-foreground", textLayerForeground);
+    document.documentElement.style.setProperty("--text-layer-opacity", textLayerOpacity.toString());
+    isTextLayerVisible = !isTextLayerVisible;
+}
+
 function loadDocument() {
     const pdfPassword = channel.getPassword();
     const loadingTask = pdfjsLib.getDocument({ url: "https://localhost/placeholder.pdf", password: pdfPassword });

app/src/main/java/app/grapheneos/pdfviewer/PdfViewer.java

@@ -51,6 +51,8 @@ import app.grapheneos.pdfviewer.viewModel.PasswordStatus;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.FileNotFoundException;
+import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.HashMap;
 import java.util.List;
 
@@ -618,15 +620,21 @@ public class PdfViewer extends AppCompatActivity implements LoaderManager.Loader
         super.onCreateOptionsMenu(menu);
         MenuInflater inflater = getMenuInflater();
         inflater.inflate(R.menu.pdf_viewer, menu);
+        if (BuildConfig.DEBUG) {
+            inflater.inflate(R.menu.pdf_viewer_debug, menu);
+        }
         return true;
     }
 
     @Override
     public boolean onPrepareOptionsMenu(@NonNull Menu menu) {
-        final int[] ids = {R.id.action_jump_to_page, R.id.action_next, R.id.action_previous,
-                R.id.action_first, R.id.action_last, R.id.action_rotate_clockwise,
-                R.id.action_rotate_counterclockwise, R.id.action_view_document_properties,
-                R.id.action_share, R.id.action_save_as};
+        final ArrayList<Integer> ids = new ArrayList<>(Arrays.asList(R.id.action_jump_to_page,
+                R.id.action_next, R.id.action_previous, R.id.action_first, R.id.action_last,
+                R.id.action_rotate_clockwise, R.id.action_rotate_counterclockwise,
+                R.id.action_view_document_properties, R.id.action_share, R.id.action_save_as));
+        if (BuildConfig.DEBUG) {
+            ids.add(R.id.debug_action_toggle_text_layer_visibility);
+        }
         if (mDocumentState < STATE_LOADED) {
             for (final int id : ids) {
                 final MenuItem item = menu.findItem(id);
@@ -691,6 +699,9 @@ public class PdfViewer extends AppCompatActivity implements LoaderManager.Loader
             return true;
         } else if (itemId == R.id.action_save_as) {
             saveDocument();
+        } else if (itemId == R.id.debug_action_toggle_text_layer_visibility) {
+            binding.webview.evaluateJavascript("toggleTextLayerVisibility()", null);
+            return true;
         }
 
         return super.onOptionsItemSelected(item);

app/src/main/res/menu/pdf_viewer_debug.xml

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="utf-8"?>
+<menu xmlns:app="http://schemas.android.com/apk/res-auto"
+    xmlns:android="http://schemas.android.com/apk/res/android">
+
+    <item
+        android:id="@+id/debug_action_toggle_text_layer_visibility"
+        android:title="@string/debug_action_toggle_text_layer_visibility"
+        app:showAsAction="never" />
+
+</menu>

app/src/main/res/values/strings.xml

@@ -14,6 +14,8 @@
     <string name="action_save_as">Save as</string>
     <string name="action_view_document_properties">Properties</string>
 
+    <string name="debug_action_toggle_text_layer_visibility">Toggle text layer visibility</string>
+
     <string name="document_properties_invalid_date">Invalid date</string>
     <string name="document_properties_retrieval_failed">Failed to obtain document metadata</string>