Tapping on an image opens pinch-to-zoom view

app/build.gradle

@@ -74,4 +74,5 @@ dependencies {
     implementation 'com.mikepenz:aboutlibraries:7.1.0'
     implementation 'com.github.di72nn.wallabag-api-wrapper:api-wrapper:v2.0.0-beta.6'
     implementation 'org.slf4j:slf4j-android:1.7.36'
+    implementation 'io.github.panpf.zoomimage:zoomimage-view:1.4.0'
 }

app/src/main/AndroidManifest.xml

@@ -55,6 +55,9 @@
             android:name="fr.gaulupeau.apps.Poche.ui.ReadArticleActivity"
             android:hardwareAccelerated="true"
             android:configChanges="keyboardHidden|orientation|screenSize"/>
+        <activity
+            android:name="fr.gaulupeau.apps.Poche.ui.ImageViewActivity"
+            android:theme="@style/Theme.AppCompat.NoActionBar" />
         <activity
             android:name="fr.gaulupeau.apps.Poche.ui.ManageArticleTagsActivity"
             android:label="@string/manageTags_title" />

app/src/main/assets/image-zoom-handler.js

@@ -0,0 +1,10 @@
+document.addEventListener("DOMContentLoaded", function() {
+    document.addEventListener("click", function(e) {
+        var target = e.target;
+        if (target.tagName === "IMG" && target.src) {
+            e.preventDefault();
+            e.stopPropagation();
+            hostImageController.onImageClicked(target.src);
+        }
+    }, true);
+});

app/src/main/java/fr/gaulupeau/apps/Poche/ui/ImageViewActivity.java

@@ -0,0 +1,136 @@
+package fr.gaulupeau.apps.Poche.ui;
+
+import android.graphics.Bitmap;
+import android.graphics.BitmapFactory;
+import android.os.Bundle;
+import android.util.Log;
+import android.view.View;
+import android.widget.ProgressBar;
+
+import androidx.appcompat.app.AppCompatActivity;
+
+import com.github.panpf.zoomimage.ZoomImageView;
+
+import java.io.ByteArrayOutputStream;
+import java.io.File;
+import java.io.InputStream;
+import java.net.URL;
+
+import fr.gaulupeau.apps.InThePoche.R;
+import fr.gaulupeau.apps.Poche.network.ImageCacheUtils;
+
+public class ImageViewActivity extends AppCompatActivity {
+
+    public static final String EXTRA_IMAGE_URL = "ImageViewActivity.imageUrl";
+    public static final String EXTRA_ARTICLE_ID = "ImageViewActivity.articleId";
+
+    private static final String TAG = ImageViewActivity.class.getSimpleName();
+
+    @Override
+    protected void onCreate(Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+        setContentView(R.layout.activity_image_view);
+
+        ZoomImageView photoView = findViewById(R.id.photoView);
+        ProgressBar progressBar = findViewById(R.id.progressBar);
+
+        String imageUrl = getIntent().getStringExtra(EXTRA_IMAGE_URL);
+        long articleId = getIntent().getLongExtra(EXTRA_ARTICLE_ID, -1);
+
+        if (imageUrl == null || imageUrl.isEmpty()) {
+            Log.w(TAG, "onCreate() no image URL");
+            finish();
+            return;
+        }
+
+        photoView.setOnClickListener(v -> finish());
+
+        new Thread(() -> {
+            Bitmap bitmap = loadBitmap(imageUrl, articleId);
+            runOnUiThread(() -> {
+                progressBar.setVisibility(View.GONE);
+                if (bitmap != null) {
+                    photoView.setImageBitmap(bitmap);
+                } else {
+                    Log.w(TAG, "onCreate() failed to load image");
+                    finish();
+                }
+            });
+        }).start();
+    }
+
+    private Bitmap loadBitmap(String imageUrl, long articleId) {
+        // Try loading from local cache first
+        if (articleId >= 0) {
+            try {
+                File file = ImageCacheUtils.getCachedImageFile(imageUrl, articleId);
+                if (file != null) {
+                    Bitmap bitmap = decodeFileScaled(file.getAbsolutePath());
+                    if (bitmap != null) return bitmap;
+                }
+            } catch (Exception e) {
+                Log.w(TAG, "loadBitmap() cache load failed", e);
+            }
+        }
+
+        // Try loading from file:// URL (cached images served to WebView)
+        if (imageUrl.startsWith("file://")) {
+            try {
+                String path = imageUrl.substring("file://".length());
+                Bitmap bitmap = decodeFileScaled(path);
+                if (bitmap != null) return bitmap;
+            } catch (Exception e) {
+                Log.w(TAG, "loadBitmap() file URL load failed", e);
+            }
+        }
+
+        // Fall back to loading from network
+        try {
+            URL url = new URL(imageUrl);
+            try (InputStream is = url.openStream()) {
+                ByteArrayOutputStream buffer = new ByteArrayOutputStream();
+                byte[] chunk = new byte[8192];
+                int n;
+                while ((n = is.read(chunk)) != -1) {
+                    buffer.write(chunk, 0, n);
+                }
+                return decodeBytesScaled(buffer.toByteArray());
+            }
+        } catch (Exception e) {
+            Log.w(TAG, "loadBitmap() remote load failed", e);
+        }
+
+        return null;
+    }
+
+    // Canvas hardware-accelerated draw limit is ~100MB; cap at 4096px (64MB @ ARGB_8888).
+    private static final int MAX_BITMAP_DIMENSION = 4096;
+
+    private static Bitmap decodeFileScaled(String path) {
+        BitmapFactory.Options options = new BitmapFactory.Options();
+        options.inJustDecodeBounds = true;
+        BitmapFactory.decodeFile(path, options);
+        options.inSampleSize = computeSampleSize(options.outWidth, options.outHeight);
+        options.inJustDecodeBounds = false;
+        return BitmapFactory.decodeFile(path, options);
+    }
+
+    private static Bitmap decodeBytesScaled(byte[] data) {
+        BitmapFactory.Options options = new BitmapFactory.Options();
+        options.inJustDecodeBounds = true;
+        BitmapFactory.decodeByteArray(data, 0, data.length, options);
+        options.inSampleSize = computeSampleSize(options.outWidth, options.outHeight);
+        options.inJustDecodeBounds = false;
+        return BitmapFactory.decodeByteArray(data, 0, data.length, options);
+    }
+
+    private static int computeSampleSize(int width, int height) {
+        int sampleSize = 1;
+        while (width > 0 && height > 0
+                && (width / sampleSize > MAX_BITMAP_DIMENSION
+                || height / sampleSize > MAX_BITMAP_DIMENSION)) {
+            sampleSize *= 2;
+        }
+        return sampleSize;
+    }
+}

app/src/main/java/fr/gaulupeau/apps/Poche/ui/ReadArticleActivity.java

@@ -22,6 +22,7 @@
 import android.webkit.WebChromeClient;
 import android.webkit.WebSettings;
 import android.webkit.WebView;
+import android.webkit.JavascriptInterface;
 import android.webkit.WebViewClient;
 import android.widget.Button;
 import android.widget.FrameLayout;
@@ -642,6 +643,7 @@ private void initWebView() {
 
         initTtsController();
         initAnnotationController();
+        initImageController();
 
         webViewContent.setWebChromeClient(new WebChromeClient() {
             private View customView;
@@ -800,6 +802,22 @@ private void initTtsController() {
         webViewContent.addJavascriptInterface(jsTtsController, "hostWebViewTextController");
     }
 
+    private void initImageController() {
+        webViewContent.addJavascriptInterface(new Object() {
+            @SuppressWarnings("unused")
+            @JavascriptInterface
+            public void onImageClicked(String imageUrl) {
+                Log.d(TAG, "onImageClicked() url: " + imageUrl);
+                Intent intent = new Intent(ReadArticleActivity.this, ImageViewActivity.class);
+                intent.putExtra(ImageViewActivity.EXTRA_IMAGE_URL, imageUrl);
+                if (article != null) {
+                    intent.putExtra(ImageViewActivity.EXTRA_ARTICLE_ID, article.getArticleId().longValue());
+                }
+                startActivity(intent);
+            }
+        }, "hostImageController");
+    }
+
     private void initAnnotationController() {
         if (!annotationsEnabled) return;
 
@@ -918,6 +936,8 @@ private String getHtmlBase() {
     private String getExtraHead() {
         String extra = "";
 
+        extra += "\n\t\t<script src=\"image-zoom-handler.js\"></script>";
+
         if (annotationsEnabled) {
             extra += "\n" +
                     "\t\t<script src=\"annotator.min.js\"></script>" +

app/src/main/res/layout/activity_image_view.xml

@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="utf-8"?>
+<FrameLayout
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    android:background="#000000">
+
+    <com.github.panpf.zoomimage.ZoomImageView
+        android:id="@+id/photoView"
+        android:layout_width="match_parent"
+        android:layout_height="match_parent" />
+
+    <ProgressBar
+        android:id="@+id/progressBar"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_gravity="center"
+        android:indeterminateTint="@android:color/white" />
+
+</FrameLayout>