Add chat filter pill fade out on slide close.

app/src/main/java/org/thoughtcrime/securesms/conversationlist/chatfilter/ConversationListFilterPullView.kt

@@ -103,6 +103,10 @@ class ConversationListFilterPullView @JvmOverloads constructor(
     } else {
       binding.filterText.translationY = 0f
     }
+
+    if (state == FilterPullState.CLOSE_APEX) {
+      binding.filterText.alpha = FilterLerp.getPillCloseApexAlphaLerp(progress)
+    }
   }
 
   fun onUserDragFinished() {

app/src/main/java/org/thoughtcrime/securesms/conversationlist/chatfilter/FilterLerp.kt

@@ -3,6 +3,7 @@ package org.thoughtcrime.securesms.conversationlist.chatfilter
 import android.animation.FloatEvaluator
 import androidx.annotation.FloatRange
 import org.signal.core.util.dp
+import org.thoughtcrime.securesms.util.Util
 
 /**
  * Centralized location for filter view linear interpolations.
@@ -37,6 +38,11 @@ object FilterLerp {
     Point(1f, FILTER_APEX * 0.55f)
   )
 
+  private val PILL_CLOSE_APEX_ALPHA_LERP = getFn(
+    Point(0.35f * FILTER_APEX / 100, 0f),
+    Point(0.7f * FILTER_APEX / 100, 1f)
+  )
+
   private fun helpTextAlphaLerp(@FloatRange(from = 0.0, to = 1.0) startFraction: Float) = getFn(
     Point(startFraction, 0f),
     Point(1f, 1f)
@@ -46,6 +52,10 @@ object FilterLerp {
     return getLerp(fraction, helpTextAlphaLerp(startFraction))
   }
 
+  fun getPillCloseApexAlphaLerp(fraction: Float): Float {
+    return Util.clamp(getLerp(fraction, PILL_CLOSE_APEX_ALPHA_LERP), 0f, 1f)
+  }
+
   /**
    * Get the LERP for the "Filter enabled" pill.
    */