From 0df58af5628bbe684414cea5df68cc1f36f82269 Mon Sep 17 00:00:00 2001
From: Meenbeese <meenbeese@tutanota.com>
Date: Wed, 7 Aug 2024 16:48:50 -0400
Subject: [PATCH] Implement faster quadratic speed scrolling

---
 .../droidify/ui/appList/AppListFragment.kt    |  7 ++-
 .../java/com/looker/core/common/Scroller.kt   | 54 +++++++++++++++++++
 2 files changed, 60 insertions(+), 1 deletion(-)
 create mode 100644 core/common/src/main/java/com/looker/core/common/Scroller.kt

diff --git a/app/src/main/kotlin/com/looker/droidify/ui/appList/AppListFragment.kt b/app/src/main/kotlin/com/looker/droidify/ui/appList/AppListFragment.kt
index 00675b86..cb658649 100644
--- a/app/src/main/kotlin/com/looker/droidify/ui/appList/AppListFragment.kt
+++ b/app/src/main/kotlin/com/looker/droidify/ui/appList/AppListFragment.kt
@@ -14,6 +14,7 @@ import androidx.lifecycle.lifecycleScope
 import androidx.lifecycle.repeatOnLifecycle
 import androidx.recyclerview.widget.LinearLayoutManager
 import androidx.recyclerview.widget.RecyclerView
+import com.looker.core.common.Scroller
 import com.looker.core.common.R as CommonR
 import com.looker.core.common.R.string as stringRes
 import com.looker.core.common.extension.dp
@@ -104,7 +105,11 @@ class AppListFragment() : Fragment(), CursorOwner.Callback {
             } else {
                 text = ""
                 setIconResource(CommonR.drawable.arrow_up)
-                setOnClickListener { recyclerView.smoothScrollToPosition(0) }
+                setOnClickListener {
+                    val scroller = Scroller(requireContext())
+                    scroller.targetPosition = 0
+                    recyclerView.layoutManager?.startSmoothScroll(scroller)
+                }
                 alpha = 0f
                 isVisible = true
                 systemBarsMargin(16.dp)
diff --git a/core/common/src/main/java/com/looker/core/common/Scroller.kt b/core/common/src/main/java/com/looker/core/common/Scroller.kt
new file mode 100644
index 00000000..22abb836
--- /dev/null
+++ b/core/common/src/main/java/com/looker/core/common/Scroller.kt
@@ -0,0 +1,54 @@
+package com.looker.core.common
+
+import android.content.Context
+import android.util.DisplayMetrics
+import android.view.View
+import androidx.recyclerview.widget.LinearSmoothScroller
+import androidx.recyclerview.widget.RecyclerView
+import kotlin.math.abs
+
+/**
+ * A custom LinearSmoothScroller that increases the scrolling speed quadratically
+ * based on the distance already scrolled.
+ *
+ * @param context The context used to access resources.
+ */
+class Scroller(context: Context) : LinearSmoothScroller(context) {
+    private var distanceScrolled = 0
+
+    /**
+     * Calculates the speed per pixel based on the display metrics and the distance
+     * already scrolled. The speed increases quadratically over time.
+     *
+     * @param displayMetrics The display metrics used to calculate the speed.
+     * @return The speed per pixel.
+     */
+    override fun calculateSpeedPerPixel(displayMetrics: DisplayMetrics): Float {
+        return (10f / displayMetrics.densityDpi) / (1 + 0.001f * distanceScrolled * distanceScrolled)
+    }
+
+    /**
+     * Called when the target view is found. Resets the distance scrolled.
+     *
+     * @param targetView The target view.
+     * @param state The current state of RecyclerView.
+     * @param action The action to be performed.
+     */
+    override fun onTargetFound(targetView: View, state: RecyclerView.State, action: Action) {
+        super.onTargetFound(targetView, state, action)
+        distanceScrolled = 0
+    }
+
+    /**
+     * Called when seeking the target step. Accumulates the distance scrolled.
+     *
+     * @param dx The amount of horizontal scroll.
+     * @param dy The amount of vertical scroll.
+     * @param state The current state of RecyclerView.
+     * @param action The action to be performed.
+     */
+    override fun onSeekTargetStep(dx: Int, dy: Int, state: RecyclerView.State, action: Action) {
+        super.onSeekTargetStep(dx, dy, state, action)
+        distanceScrolled += abs(dy)
+    }
+}