update thread lines

app/build.gradle

@@ -1,5 +1,6 @@
 plugins {
     id 'com.android.application'
+    id 'kotlin-android'
 }
 def flavor
 android {

app/src/main/java/app/fedilab/android/helper/RecyclerViewThreadLines.kt

@@ -0,0 +1,147 @@
+package app.fedilab.android.helper
+
+import android.content.Context
+import android.content.res.Resources
+import android.graphics.Canvas
+import android.graphics.DashPathEffect
+import android.graphics.Paint
+import android.graphics.Rect
+import android.view.View
+import androidx.core.content.res.ResourcesCompat
+import androidx.preference.PreferenceManager
+import androidx.recyclerview.widget.DividerItemDecoration
+import androidx.recyclerview.widget.RecyclerView
+import app.fedilab.android.R
+import app.fedilab.android.helper.RecyclerViewThreadLines.LineInfo
+import app.fedilab.android.client.mastodon.entities.Context as StatusContext
+
+class RecyclerViewThreadLines(context: Context, private val lineInfoList: List<LineInfo>) : DividerItemDecoration(context, VERTICAL) {
+    private val lineColors = threadLineColors.map { ResourcesCompat.getColor(context.resources, it, context.theme) }
+    private val dashPathEffect = DashPathEffect(floatArrayOf(3.dpToPx, 3.dpToPx), 0F)
+    private val borderColor = lineColors[0]
+    private val commonPaint = Paint().apply {
+        isDither = false
+        strokeWidth = 1.5F.dpToPx
+        strokeCap = Paint.Cap.BUTT
+        strokeJoin = Paint.Join.MITER
+        color = borderColor
+    }
+    private val maxLevel = lineColors.size
+    private val fontScale = PreferenceManager.getDefaultSharedPreferences(context).getFloat(context.getString(R.string.SET_FONT_SCALE), 1.1f).toInt()
+    private val baseMargin: Int = 6.dpToPx.toInt()
+    private val margin: Int = baseMargin * fontScale
+
+    override fun getItemOffsets(outRect: Rect, view: View, parent: RecyclerView, state: RecyclerView.State) {
+        val position = (view.layoutParams as RecyclerView.LayoutParams).viewLayoutPosition
+        val level = lineInfoList[position].level
+        val startMargin = margin * level + margin * fontScale
+        if (parent.layoutDirection == View.LAYOUT_DIRECTION_LTR) outRect.left = startMargin else outRect.right = startMargin
+    }
+
+    override fun onDraw(c: Canvas, parent: RecyclerView, state: RecyclerView.State) {
+        val childCount = parent.childCount
+        for (i in 0 until childCount) {
+            val view = parent.getChildAt(i)
+            val position = parent.getChildAdapterPosition(view)
+            val lineInfo = lineInfoList[position]
+            val level = lineInfo.level
+
+            for (j in 1..level) {
+                val lineMargin = margin * j + 3.dpToPx
+                val lineStart = if (parent.layoutDirection == View.LAYOUT_DIRECTION_LTR) lineMargin else c.width - lineMargin
+                var lineTop: Float = (view.top - baseMargin).toFloat()
+                if (j == 0) lineTop += view.height / 2
+                val paint = Paint(commonPaint)
+                paint.color = lineColors[j - 1]
+
+                // draw lines for below statuses
+                if (j != level && j >= lineInfo.fullLinesStart && j <= lineInfo.fullLinesEnd)
+                    c.drawLine(lineStart, lineTop, lineStart, view.bottom.toFloat(), paint)
+
+                // draw vertical line for current statuses
+                if (j == level) {
+                    // top the line starts at the middle of the above status
+                    if (i > 0) lineTop -= parent.getChildAt(i - 1).height / 2 - 1 // '- 1' is to prevent overlapping with above horizontal line
+
+                    // bottom of the line ends at the middle of the current status
+                    var lineBottom = view.bottom.toFloat() - view.height / 2
+
+                    // if below status has a full line for current level, extend the line to the bottom
+                    if (i < childCount - 1) {
+                        val nextLineInfo = lineInfoList[position + 1]
+                        if (level >= nextLineInfo.fullLinesStart && level <= nextLineInfo.fullLinesEnd) {
+                            lineBottom = view.bottom.toFloat()
+                        }
+                    }
+
+                    // if level is max, use a dashed line
+                    if (j == maxLevel) paint.pathEffect = dashPathEffect
+
+                    c.drawLine(lineStart, lineTop, lineStart, lineBottom, paint)
+                }
+
+                // draw horizontal line for current statuses
+                if (j == level) {
+                    lineTop = view.bottom.toFloat() - view.height / 2
+                    val lineEnd = lineStart + margin * 2
+                    c.drawLine(lineStart - 1, lineTop, lineEnd, lineTop, paint) // 'lineStart - 1' is to properly connect with the vertical line
+                }
+            }
+        }
+    }
+
+    data class LineInfo(var level: Int, var end: Boolean, var fullLinesStart: Int, var fullLinesEnd: Int)
+
+    private val Int.dpToPx: Float
+        get() = this * Resources.getSystem().displayMetrics.density
+
+    private val Float.dpToPx: Float
+        get() = this * Resources.getSystem().displayMetrics.density
+
+    companion object {
+        val threadLineColors = listOf(R.color.decoration_1, R.color.decoration_2, R.color.decoration_3, R.color.decoration_4, R.color.decoration_5)
+    }
+}
+
+fun getThreadDecorationInfo(fediContext: StatusContext, selectedStatusId: String): MutableList<LineInfo> {
+    val lineInfoList = mutableListOf<LineInfo>()
+    repeat(fediContext.ancestors.size) { lineInfoList.add(LineInfo(0, true, 0, 0)) }
+    lineInfoList.add(LineInfo(0, fediContext.descendants.isNotEmpty(), 0, 0))
+    val descendantsLineInfoList = List(fediContext.descendants.size) { LineInfo(0, false, 0, 0) }
+    for (i in fediContext.descendants.indices) {
+        fediContext.descendants[i].let { status ->
+            var level = 0
+            if (status.in_reply_to_id != null) {
+                if (status.in_reply_to_id == selectedStatusId)
+                    level = 1
+                else {
+                    var replyToId: String? = status.in_reply_to_id
+                    while (replyToId != null && level < RecyclerViewThreadLines.threadLineColors.size) {
+                        level += 1
+                        replyToId = fediContext.descendants.firstOrNull { it.id == replyToId }?.in_reply_to_id
+                    }
+                }
+            }
+            descendantsLineInfoList[i].level = level
+            val firstReply = fediContext.descendants.firstOrNull { it.in_reply_to_id == status.id }
+            if (firstReply == null) descendantsLineInfoList[i].end = true
+        }
+    }
+    for (i in descendantsLineInfoList.indices) {
+        var fullLinesStart = descendantsLineInfoList[i].level
+        var fullLinesEnd = descendantsLineInfoList[i].level
+        var fullLinesEndSet = false
+        for (j in i + 1 until descendantsLineInfoList.lastIndex) {
+            if (!fullLinesEndSet && descendantsLineInfoList[j].level < descendantsLineInfoList[i].level) {
+                fullLinesEnd = descendantsLineInfoList[j].level
+                fullLinesEndSet = true
+            }
+            fullLinesStart = descendantsLineInfoList[j].level.coerceAtMost(fullLinesStart)
+        }
+        descendantsLineInfoList[i].fullLinesStart = fullLinesStart
+        descendantsLineInfoList[i].fullLinesEnd = fullLinesEnd
+    }
+
+    lineInfoList.addAll(descendantsLineInfoList)
+    return lineInfoList
+}

app/src/main/java/app/fedilab/android/ui/fragment/timeline/FragmentMastodonContext.java

@@ -16,6 +16,7 @@ package app.fedilab.android.ui.fragment.timeline;
 
 import static app.fedilab.android.activities.ContextActivity.displayCW;
 import static app.fedilab.android.activities.ContextActivity.expand;
+import static app.fedilab.android.helper.RecyclerViewThreadLinesKt.getThreadDecorationInfo;
 
 import android.content.BroadcastReceiver;
 import android.content.Intent;
@@ -43,8 +44,9 @@ import app.fedilab.android.client.entities.Timeline;
 import app.fedilab.android.client.mastodon.entities.Context;
 import app.fedilab.android.client.mastodon.entities.Status;
 import app.fedilab.android.databinding.FragmentPaginationBinding;
-import app.fedilab.android.helper.DividerDecoration;
 import app.fedilab.android.helper.Helper;
+import app.fedilab.android.helper.RecyclerViewThreadLines;
+import app.fedilab.android.helper.RecyclerViewThreadLines.LineInfo;
 import app.fedilab.android.helper.SpannableHelper;
 import app.fedilab.android.helper.ThemeHelper;
 import app.fedilab.android.ui.drawer.StatusAdapter;
@@ -252,7 +254,8 @@ public class FragmentMastodonContext extends Fragment {
                 binding.recyclerView.removeItemDecorationAt(i);
             }
         }
-        binding.recyclerView.addItemDecoration(new DividerDecoration(requireActivity(), statuses));
+        List<LineInfo> threadDecorationInfo = getThreadDecorationInfo(context, focusedStatus.id);
+        binding.recyclerView.addItemDecoration(new RecyclerViewThreadLines(requireContext(), threadDecorationInfo));
         binding.swipeContainer.setRefreshing(false);
         binding.recyclerView.scrollToPosition(statusPosition);
     }

build.gradle

@@ -6,6 +6,7 @@ buildscript {
     }
     dependencies {
         classpath 'com.android.tools.build:gradle:7.0.4'
+        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:1.6.21"
 
         // NOTE: Do not place your application dependencies here; they belong
         // in the individual module build.gradle files