Android: Rate limit refreshInputOverlay calls from sliders

Sliders can trigger change listeners very rapidly, so let's add some
rate limiting so dragging a slider doesn't cause the whole UI to lag.
(Now the input overlay looks laggy when dragging a slider, though.)

Source/Android/app/src/main/java/org/dolphinemu/dolphinemu/activities/EmulationActivity.kt

@@ -8,6 +8,8 @@ import android.graphics.Rect
 import android.net.Uri
 import android.os.Build
 import android.os.Bundle
+import android.os.Handler
+import android.os.Looper
 import android.util.SparseIntArray
 import android.view.KeyEvent
 import android.view.MenuItem
@@ -61,6 +63,7 @@ import org.dolphinemu.dolphinemu.ui.main.ThemeProvider
 import org.dolphinemu.dolphinemu.utils.AfterDirectoryInitializationRunner
 import org.dolphinemu.dolphinemu.utils.DirectoryInitialization
 import org.dolphinemu.dolphinemu.utils.FileBrowserHelper
+import org.dolphinemu.dolphinemu.utils.RateLimiter
 import org.dolphinemu.dolphinemu.utils.ThemeHelper
 import kotlin.math.roundToInt
 
@@ -88,6 +91,10 @@ class EmulationActivity : AppCompatActivity(), ThemeProvider {
 
     private lateinit var binding: ActivityEmulationBinding
 
+    private val refreshInputOverlayRateLimiter = RateLimiter(Handler(Looper.getMainLooper()), 100) {
+        emulationFragment?.refreshInputOverlay()
+    }
+
     private val requestChangeDisc = registerForActivityResult(
         ActivityResultContracts.GetContent()
     ) { uri: Uri? ->
@@ -729,7 +736,7 @@ class EmulationActivity : AppCompatActivity(), ThemeProvider {
                 addOnChangeListener { _: Slider?, value: Float, _: Boolean ->
                     dialogBinding.inputScaleValue.text = "${(value.toInt() + 50)}%"
                     IntSetting.MAIN_CONTROL_SCALE.setInt(settings, value.toInt())
-                    emulationFragment?.refreshInputOverlay()
+                    refreshInputOverlayRateLimiter.run()
                 }
             }
             inputScaleValue.text =
@@ -742,7 +749,7 @@ class EmulationActivity : AppCompatActivity(), ThemeProvider {
                 addOnChangeListener { _: Slider?, value: Float, _: Boolean ->
                     inputOpacityValue.text = value.toInt().toString() + "%"
                     IntSetting.MAIN_CONTROL_OPACITY.setInt(settings, value.toInt())
-                    emulationFragment?.refreshInputOverlay()
+                    refreshInputOverlayRateLimiter.run()
                 }
             }
             inputOpacityValue.text = inputOpacitySlider.value.toInt().toString() + "%"

Source/Android/app/src/main/java/org/dolphinemu/dolphinemu/utils/RateLimiter.kt

@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+package org.dolphinemu.dolphinemu.utils
+
+import android.os.Handler
+import android.os.SystemClock
+
+class RateLimiter(
+    private val handler: Handler,
+    private val delayBetweenRunsMs: Int,
+    private val runnable: Runnable
+)  {
+    private var nextAllowedRun = 0L
+    private var pendingRun = false
+
+    fun run() {
+        if (!pendingRun) {
+            val time = SystemClock.uptimeMillis()
+            if (time >= nextAllowedRun) {
+                runnable.run()
+                nextAllowedRun = time + delayBetweenRunsMs
+            } else {
+                pendingRun = true
+                handler.postAtTime({
+                    runnable.run()
+                    nextAllowedRun = SystemClock.uptimeMillis() + delayBetweenRunsMs
+                    pendingRun = false
+                }, nextAllowedRun)
+            }
+        }
+    }
+}