Improve spoiler performance by stopping animation when backgrounded.

app/src/main/java/org/thoughtcrime/securesms/components/spoiler/SpoilerRendererDelegate.kt

@@ -10,19 +10,26 @@ import android.view.View.OnAttachStateChangeListener
 import android.view.animation.LinearInterpolator
 import android.widget.TextView
 import androidx.core.content.ContextCompat
+import androidx.lifecycle.DefaultLifecycleObserver
+import androidx.lifecycle.LifecycleOwner
 import org.signal.core.util.dp
 import org.thoughtcrime.securesms.R
 import org.thoughtcrime.securesms.components.spoiler.SpoilerAnnotation.SpoilerClickableSpan
+import org.thoughtcrime.securesms.util.getLifecycle
 
 /**
  * Performs initial calculation on how to render spoilers and then delegates to actually drawing the spoiler sparkles.
  */
-class SpoilerRendererDelegate @JvmOverloads constructor(private val view: TextView, private val renderForComposing: Boolean = false) {
+class SpoilerRendererDelegate @JvmOverloads constructor(
+  private val view: TextView,
+  private val renderForComposing: Boolean = false
+) {
 
   private val renderer: SpoilerRenderer
   private val spoilerDrawable: SpoilerDrawable
   private var animatorRunning = false
   private var textColor: Int
+  private var canAnimate = false
 
   private val cachedAnnotations = HashMap<Int, Map<Annotation, SpoilerClickableSpan?>>()
   private val cachedMeasurements = HashMap<Int, SpanMeasurements>()
@@ -50,7 +57,18 @@ class SpoilerRendererDelegate @JvmOverloads constructor(private val view: TextVi
 
     view.addOnAttachStateChangeListener(object : OnAttachStateChangeListener {
       override fun onViewDetachedFromWindow(v: View) = stopAnimating()
-      override fun onViewAttachedToWindow(v: View) = Unit
+      override fun onViewAttachedToWindow(v: View) {
+        view.getLifecycle().addObserver(object : DefaultLifecycleObserver {
+          override fun onResume(owner: LifecycleOwner) {
+            canAnimate = true
+          }
+
+          override fun onPause(owner: LifecycleOwner) {
+            canAnimate = false
+            stopAnimating()
+          }
+        })
+      }
     })
   }
 
@@ -63,6 +81,10 @@ class SpoilerRendererDelegate @JvmOverloads constructor(private val view: TextVi
   }
 
   fun draw(canvas: Canvas, text: Spanned, layout: Layout) {
+    if (!canAnimate) {
+      return
+    }
+
     var hasSpoilersToRender = false
     val annotations: Map<Annotation, SpoilerClickableSpan?> = cachedAnnotations.getFromCache(text) { SpoilerAnnotation.getSpoilerAndClickAnnotations(text) }