Add flag for caching text truncation

Reviewed By: adityasharat

Differential Revision: D75162864

fbshipit-source-id: 92f0d918326e84e146172769977acdd2f73c38fe

Author: astreet

litho-rendercore-text/src/main/java/com/facebook/rendercore/text/RichTextPrimitive.kt

@@ -16,6 +16,7 @@
 
 package com.facebook.rendercore.text
 
+import android.graphics.Rect
 import androidx.core.util.component1
 import androidx.core.util.component2
 import com.facebook.rendercore.RenderCoreConfig
@@ -36,10 +37,12 @@ fun RichTextPrimitive(
     id: Long,
     text: CharSequence,
     style: TextStyle,
-    usePerformantTruncation: Boolean = RenderCoreConfig.usePerformantTruncation
+    usePerformantTruncation: Boolean = RenderCoreConfig.usePerformantTruncation,
+    useTruncationCaching: Boolean = RenderCoreConfig.useTruncationCaching,
 ): Primitive {
   return Primitive(
-      layoutBehavior = RichTextLayoutBehavior(text, style, usePerformantTruncation),
+      layoutBehavior =
+          RichTextLayoutBehavior(text, style, usePerformantTruncation, useTruncationCaching),
       mountBehavior =
           MountBehavior(
               id = id,
@@ -50,8 +53,8 @@ fun RichTextPrimitive(
                   ) { c ->
                     RCTextView(c)
                   }) {
-                bindWithLayoutData<TextLayout>(Unit) { content, textLayout ->
-                  content.mount(textLayout)
+                bindWithLayoutData<RichTextLayoutData>(Unit) { content, layoutData ->
+                  content.mount(layoutData.textLayout)
                   onUnbind { content.unmount() }
                 }
               })
@@ -60,9 +63,26 @@ fun RichTextPrimitive(
 private class RichTextLayoutBehavior(
     val text: CharSequence,
     val style: TextStyle,
-    val usePerformantTruncation: Boolean
+    val usePerformantTruncation: Boolean,
+    val useTruncationCaching: Boolean,
 ) : LayoutBehavior {
   override fun LayoutScope.layout(sizeConstraints: SizeConstraints): PrimitiveLayoutResult {
+    val previousRichTextLayoutData = previousLayoutData as? RichTextLayoutData
+    if (useTruncationCaching &&
+        previousRichTextLayoutData != null &&
+        canReuseTextLayout(previousRichTextLayoutData, text, style, sizeConstraints)) {
+      return PrimitiveLayoutResult(
+          width = max(previousRichTextLayoutData.size.width(), sizeConstraints.minWidth),
+          height = max(previousRichTextLayoutData.size.height(), sizeConstraints.minHeight),
+          // TODO: This should copy the textLayout with new clickable spans
+          layoutData =
+              RichTextLayoutData(
+                  previousRichTextLayoutData.textLayout,
+                  previousRichTextLayoutData.size,
+                  style,
+                  sizeConstraints))
+    }
+
     val (size, textLayout) =
         layout(
             androidContext,
@@ -71,14 +91,55 @@ private class RichTextLayoutBehavior(
             text,
             style,
             usePerformantTruncation)
-
     return PrimitiveLayoutResult(
         width = max(size.width(), sizeConstraints.minWidth),
         height = max(size.height(), sizeConstraints.minHeight),
-        layoutData = textLayout)
+        layoutData = RichTextLayoutData(textLayout, size, style, sizeConstraints))
+  }
+
+  private fun canReuseTextLayout(
+      previousLayoutData: RichTextLayoutData,
+      text: CharSequence,
+      style: TextStyle,
+      sizeConstraints: SizeConstraints
+  ): Boolean {
+    return previousLayoutData.textLayout.isExplicitlyTruncated &&
+        previousLayoutData.sizeConstraints == sizeConstraints &&
+        hasEquivalentStyle(style, previousLayoutData.style) &&
+        hasEquivalentTruncatedText(previousLayoutData.textLayout, text, style)
+  }
+
+  // TODO: this should be moved to TextStyle and emcompass all properties
+  fun hasEquivalentStyle(style1: TextStyle, style2: TextStyle): Boolean {
+    return style1.textSize == style2.textSize &&
+        style1.textColor == style2.textColor &&
+        style1.textDirection == style2.textDirection &&
+        style1.textStyle == style2.textStyle &&
+        style1.truncationStyle == style2.truncationStyle
+  }
+
+  private fun hasEquivalentTruncatedText(
+      textLayout: TextLayout,
+      text: CharSequence,
+      style: TextStyle
+  ): Boolean {
+    if (!textLayout.isExplicitlyTruncated) {
+      return false
+    }
+    val textLayoutText = textLayout.layout.text
+    val suffix = style.customEllipsisText ?: ""
+    return textLayoutText.endsWith(suffix) &&
+        text.startsWith(textLayoutText.subSequence(0, textLayoutText.length - suffix.length))
   }
 }
 
+private class RichTextLayoutData(
+    val textLayout: TextLayout,
+    val size: Rect,
+    val style: TextStyle,
+    val sizeConstraints: SizeConstraints
+)
+
 object RichTextPrimitiveConfig {
   val canPreallocation: Boolean = true
   val poolSize: Int = 10

litho-rendercore/src/main/java/com/facebook/rendercore/RenderCoreConfig.kt

@@ -50,4 +50,7 @@ object RenderCoreConfig {
 
   /** Flag to use getOffsetForAdvance in TextMeasurementUtils to prevent ANRs. */
   @JvmField var usePerformantTruncation: Boolean = false
+
+  /** Flag to re-use compatible TextLayouts in truncation scenarios. */
+  @JvmField var useTruncationCaching: Boolean = false
 }

litho-widget/src/main/java/com/facebook/litho/widget/RichText.kt

@@ -29,15 +29,21 @@ class RichText(
     val text: CharSequence,
     val textStyle: TextStyle? = null,
     private val style: Style? = null,
-    private val usePerformantTruncation: Boolean = RenderCoreConfig.usePerformantTruncation
+    private val usePerformantTruncation: Boolean = RenderCoreConfig.usePerformantTruncation,
+    private val useTruncationCaching: Boolean = RenderCoreConfig.useTruncationCaching
 ) : PrimitiveComponent() {
   override fun PrimitiveComponentScope.render(): LithoPrimitive {
     val resolvedTextStyle =
         useCached(textStyle) {
           textStyle ?: TextStyle.createDefaultConfiguredTextStyle(androidContext)
         }
     return LithoPrimitive(
-        RichTextPrimitive(createPrimitiveId(), text, resolvedTextStyle, usePerformantTruncation),
+        RichTextPrimitive(
+            createPrimitiveId(),
+            text,
+            resolvedTextStyle,
+            usePerformantTruncation,
+            useTruncationCaching),
         style = style)
   }
 }