GrapheneOS · amusergrieve · Apr 4, 2025
diff --git a/app/src/main/java/app/grapheneos/pdfviewer/PdfViewer.java b/app/src/main/java/app/grapheneos/pdfviewer/PdfViewer.java
@@ -50,6 +50,7 @@
 import app.grapheneos.pdfviewer.databinding.PdfviewerBinding;
 import app.grapheneos.pdfviewer.fragment.DocumentPropertiesFragment;
 import app.grapheneos.pdfviewer.fragment.JumpToPageFragment;
+import app.grapheneos.pdfviewer.fragment.SetZoomFragment;
 import app.grapheneos.pdfviewer.fragment.PasswordPromptFragment;
 import app.grapheneos.pdfviewer.ktx.ViewKt;
 import app.grapheneos.pdfviewer.loader.DocumentPropertiesAsyncTaskLoader;
@@ -443,12 +444,12 @@ public boolean onTapUp() {
 
                     @Override
                     public void onZoom(float scaleFactor, float focusX, float focusY) {
-                        zoom(scaleFactor, focusX, focusY, false);
+                        onZoomPage(scaleFactor, focusX, focusY, false);
                     }
 
                     @Override
                     public void onZoomEnd() {
-                        zoomEnd();
+                        onZoomPageEnd();
                     }
                 });
 
@@ -643,15 +644,15 @@ private void shareDocument() {
         }
     }
 
-    private void zoom(float scaleFactor, float focusX, float focusY, boolean end) {
+    public void onZoomPage(float scaleFactor, float focusX, float focusY, boolean end) {
         mZoomRatio = Math.min(Math.max(mZoomRatio * scaleFactor, MIN_ZOOM_RATIO), MAX_ZOOM_RATIO);
         mZoomFocusX = focusX;
         mZoomFocusY = focusY;
         renderPage(end ? 1 : 2);
         invalidateOptionsMenu();
     }
 
-    private void zoomEnd() {
+    public void onZoomPageEnd() {
         renderPage(1);
     }
 
@@ -721,7 +722,7 @@ public boolean onPrepareOptionsMenu(@NonNull Menu menu) {
                 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,
-                R.id.action_outline));
+                R.id.action_outline, R.id.action_set_zoom));
         if (BuildConfig.DEBUG) {
             ids.add(R.id.debug_action_toggle_text_layer_visibility);
             ids.add(R.id.debug_action_crash_webview);
@@ -750,6 +751,7 @@ public boolean onPrepareOptionsMenu(@NonNull Menu menu) {
         enableDisableMenuItem(menu.findItem(R.id.action_next), mPage < mNumPages);
         enableDisableMenuItem(menu.findItem(R.id.action_previous), mPage > 1);
         enableDisableMenuItem(menu.findItem(R.id.action_save_as), mUri != null);
+        enableDisableMenuItem(menu.findItem(R.id.action_set_zoom), mUri != null);
         enableDisableMenuItem(menu.findItem(R.id.action_view_document_properties),
                 mDocumentProperties != null);
 
@@ -807,6 +809,13 @@ public boolean onOptionsItemSelected(MenuItem item) {
             new JumpToPageFragment()
                 .show(getSupportFragmentManager(), JumpToPageFragment.TAG);
             return true;
+        } else if (itemId == R.id.action_set_zoom) {
+            SetZoomFragment zoomFragment = new SetZoomFragment(mZoomRatio, MIN_ZOOM_RATIO, MAX_ZOOM_RATIO);
+            // TODO: horizontally center the zooming focus.
+            //  Need to get the coordinates of viewport top-center.
+            // zoomFragment.setZoomFocusX((float) binding.webview.getWidth() / 2);
+            zoomFragment.show(getSupportFragmentManager(), SetZoomFragment.TAG);
+            return true;
         } else if (itemId == R.id.action_share) {
             shareDocument();
             return true;

diff --git a/app/src/main/java/app/grapheneos/pdfviewer/fragment/SetZoomFragment.kt b/app/src/main/java/app/grapheneos/pdfviewer/fragment/SetZoomFragment.kt
@@ -0,0 +1,125 @@
+package app.grapheneos.pdfviewer.fragment
+
+import android.app.Dialog
+import android.content.DialogInterface
+import android.os.Bundle
+import android.view.Gravity
+import android.widget.FrameLayout
+import android.widget.LinearLayout
+import android.widget.SeekBar
+import android.widget.TextView
+import androidx.core.view.marginTop
+import androidx.fragment.app.DialogFragment
+import app.grapheneos.pdfviewer.PdfViewer
+import com.google.android.material.dialog.MaterialAlertDialogBuilder
+import kotlin.math.ln
+import kotlin.math.pow
+
+class SetZoomFragment(
+    private var mCurrentViewerZoomRatio: Double,
+    private var mMinZoomRatio: Double,
+    private var mMaxZoomRatio: Double,
+) : DialogFragment() {
+
+    companion object {
+        const val TAG = "SetZoomFragment"
+        private const val STATE_SEEKBAR_CUR = "seekbar_cur"
+        private const val STATE_SEEKBAR_MIN = "seekbar_min"
+        private const val STATE_SEEKBAR_MAX = "seekbar_max"
+        private const val STATE_VIEWER_CUR = "viewer_cur"
+        private const val STATE_VIEWER_MIN = "viewer_min"
+        private const val STATE_VIEWER_MAX = "viewer_max"
+        private const val STATE_ZOOM_FOCUSX = "viewer_zoom_focusx"
+        private const val STATE_ZOOM_FOCUSY = "viewer_zoom_focusy"
+        private const val SEEKBAR_RESOLUTION = 1024
+    }
+
+    private val mSeekBar: SeekBar by lazy { SeekBar(requireActivity()) }
+    private val mZoomLevelText: TextView by lazy { TextView(requireActivity()) }
+
+    private var mZoomFocusX: Float = 0.0f
+    public fun setZoomFocusX(value: Float) {mZoomFocusX = value}
+    private var mZoomFocusY: Float = 0.0f
+    public fun setZoomFocusY(value: Float) {mZoomFocusY = value}
+
+    private fun progressToZoom(progress: Int): Double {
+        val progressClip = progress.coerceAtLeast(0).coerceAtMost(SEEKBAR_RESOLUTION);
+        return mMinZoomRatio * (mMaxZoomRatio / mMinZoomRatio).pow(progressClip.toDouble() / SEEKBAR_RESOLUTION)
+    }
+
+    private fun zoomToProgress(zoom: Double): Int {
+        val zoomClip = zoom.coerceAtLeast(mMinZoomRatio).coerceAtMost(mMaxZoomRatio);
+        return (SEEKBAR_RESOLUTION * ln(zoomClip / mMinZoomRatio) / ln(mMaxZoomRatio / mMinZoomRatio)).toInt()
+    }
+
+    fun refreshZoomText(progress: Int) {
+        mZoomLevelText.text = "${(progressToZoom(progress) * 100).toInt()}%"
+    }
+
+    override fun onCreateDialog(savedInstanceState: Bundle?): Dialog {
+
+        val viewerActivity: PdfViewer = (requireActivity() as PdfViewer)
+
+        if (savedInstanceState != null) {
+            val progress = savedInstanceState.getInt(STATE_SEEKBAR_CUR)
+            mSeekBar.setMin(savedInstanceState.getInt(STATE_SEEKBAR_MIN))
+            mSeekBar.setMax(savedInstanceState.getInt(STATE_SEEKBAR_MAX))
+            mSeekBar.progress = progress
+            refreshZoomText(progress)
+            mCurrentViewerZoomRatio = savedInstanceState.getDouble(STATE_VIEWER_CUR)
+            mMinZoomRatio = savedInstanceState.getDouble(STATE_VIEWER_MIN)
+            mMaxZoomRatio = savedInstanceState.getDouble(STATE_VIEWER_MAX)
+            mZoomFocusX = savedInstanceState.getFloat(STATE_ZOOM_FOCUSX)
+            mZoomFocusY = savedInstanceState.getFloat(STATE_ZOOM_FOCUSY)
+        } else {
+            mSeekBar.setMin(0)
+            mSeekBar.setMax(SEEKBAR_RESOLUTION)
+            val progress = zoomToProgress(mCurrentViewerZoomRatio)
+            mSeekBar.setProgress(progress)
+            refreshZoomText(progress)
+        }
+        mSeekBar.setOnSeekBarChangeListener(object : SeekBar.OnSeekBarChangeListener {
+            override fun onProgressChanged(seekBar: SeekBar?, progress: Int, fromUser: Boolean) {
+                refreshZoomText(progress)
+            }
+
+            override fun onStartTrackingTouch(seekBar: SeekBar?) {}
+            override fun onStopTrackingTouch(seekBar: SeekBar?) {}
+        })
+        val layout = LinearLayout(requireActivity())
+        layout.orientation = LinearLayout.VERTICAL
+        layout.gravity = Gravity.CENTER
+        val textParams = LinearLayout.LayoutParams(
+            LinearLayout.LayoutParams.WRAP_CONTENT,
+            LinearLayout.LayoutParams.WRAP_CONTENT,
+        )
+        textParams.setMargins(0, 24, 0, 0) // Margin above the text
+        layout.addView(mZoomLevelText, textParams)
+        layout.addView(
+            mSeekBar, LinearLayout.LayoutParams(
+                LinearLayout.LayoutParams.MATCH_PARENT,
+                LinearLayout.LayoutParams.WRAP_CONTENT,
+            )
+        )
+        return MaterialAlertDialogBuilder(requireActivity())
+            .setView(layout)
+            .setPositiveButton(android.R.string.ok) { _: DialogInterface?, _: Int ->
+                mSeekBar.clearFocus()
+                val zoom = progressToZoom(mSeekBar.progress)
+                viewerActivity.onZoomPage((zoom / mCurrentViewerZoomRatio).toFloat(), mZoomFocusX, mZoomFocusY, true)
+            }
+            .setNegativeButton(android.R.string.cancel, null)
+            .create()
+    }
+
+    override fun onSaveInstanceState(outState: Bundle) {
+        outState.putInt(STATE_SEEKBAR_CUR, mSeekBar.progress)
+        outState.putInt(STATE_SEEKBAR_MIN, mSeekBar.min)
+        outState.putInt(STATE_SEEKBAR_MAX, mSeekBar.max)
+        outState.putDouble(STATE_VIEWER_CUR, mCurrentViewerZoomRatio)
+        outState.putDouble(STATE_VIEWER_MIN, mMinZoomRatio)
+        outState.putDouble(STATE_VIEWER_MAX, mMaxZoomRatio)
+        outState.putFloat(STATE_ZOOM_FOCUSX, mZoomFocusX)
+        outState.putFloat(STATE_ZOOM_FOCUSY, mZoomFocusY)
+    }
+}
diff --git a/app/src/main/res/drawable/ic_zoom_in_24dp.xml b/app/src/main/res/drawable/ic_zoom_in_24dp.xml
@@ -0,0 +1,12 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="24dp"
+    android:height="24dp"
+    android:viewportWidth="24"
+    android:viewportHeight="24">
+    <path
+        android:fillColor="?attr/colorControlNormal"
+        android:pathData="M12.43 9.18h-1.438V7.754a0.83 0.83 0 0 0 -0.832 -0.828 0.826 0.826 0 0 0 -0.816 0.828V9.18H7.906a0.844 0.844 0 0 0 -0.828 0.828c0.012 0.46 0.383 0.832 0.828 0.832h1.438v1.426c0 0.457 0.37 0.828 0.816 0.828a0.83 0.83 0 0 0 0.832 -0.828V10.84h1.438a0.827 0.827 0 0 0 0.816 -0.832 0.826 0.826 0 0 0 -0.816 -0.828m0 0" />
+    <path
+        android:fillColor="?attr/colorControlNormal"
+        android:pathData="M19.773 17.059l-3.68 -3.692c-0.046 -0.05 -0.109 -0.097 -0.171 -0.148a6.4 6.4 0 0 0 0.828 -3.172c0 -3.617 -2.945 -6.555 -6.566 -6.555a6.56 6.56 0 0 0 -6.555 6.555c0 3.617 2.937 6.566 6.555 6.566a6.5 6.5 0 0 0 2.828 -0.644c0.058 0.101 0.133 0.187 0.222 0.273l3.68 3.68c0.793 0.781 2.082 0.781 2.86 0a2.02 2.02 0 0 0 0 -2.863m-9.59 -2.973a4.037 4.037 0 0 1 -4.027 -4.04 4.034 4.034 0 0 1 4.028 -4.026c2.23 0 4.039 1.808 4.039 4.027a4.04 4.04 0 0 1 -4.04 4.039m0 0" />
+</vector>
diff --git a/app/src/main/res/menu/pdf_viewer.xml b/app/src/main/res/menu/pdf_viewer.xml
@@ -43,6 +43,12 @@
         android:title="@string/action_jump_to_page"
         app:showAsAction="ifRoom" />
 
+    <item
+        android:id="@+id/action_set_zoom"
+        android:icon="@drawable/ic_zoom_in_24dp"
+        android:title="@string/action_set_zoom"
+        app:showAsAction="ifRoom" />
+
     <item
         android:id="@+id/action_rotate_clockwise"
         android:icon="@drawable/ic_rotate_right_24dp"

diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
@@ -8,6 +8,7 @@
     <string name="action_first">First page</string>
     <string name="action_last">Last page</string>
     <string name="action_jump_to_page">Jump to page</string>
+    <string name="action_set_zoom">Zoom</string>
     <string name="action_rotate_clockwise">Rotate clockwise</string>
     <string name="action_rotate_counterclockwise">Rotate counterclockwise</string>
     <string name="action_share">Share</string>