[markdown][compose] IJPL-175966 Provide smoother animation

GitOrigin-RevId: 12880ed9794077b5f6ad185fe38c25113f1d53a2

platform/jewel/markdown/core/api-dump-unreviewed.txt

@@ -581,6 +581,7 @@ a:org.jetbrains.jewel.markdown.scrolling.ScrollingSynchronizer
 - pa:afterProcessing():V
 - pa:beforeProcessing():V
 - f:process(kotlin.jvm.functions.Function0):java.lang.Object
-- a:scrollToLine(I,kotlin.coroutines.Continuation):java.lang.Object
+- a:scrollToLine(I,androidx.compose.animation.core.AnimationSpec,kotlin.coroutines.Continuation):java.lang.Object
+- bs:scrollToLine$default(org.jetbrains.jewel.markdown.scrolling.ScrollingSynchronizer,I,androidx.compose.animation.core.AnimationSpec,kotlin.coroutines.Continuation,I,java.lang.Object):java.lang.Object
 f:org.jetbrains.jewel.markdown.scrolling.ScrollingSynchronizer$Companion
 - f:create(androidx.compose.foundation.gestures.ScrollableState):org.jetbrains.jewel.markdown.scrolling.ScrollingSynchronizer

platform/jewel/markdown/core/src/main/kotlin/org/jetbrains/jewel/markdown/scrolling/ScrollingSynchronizer.kt

@@ -2,6 +2,8 @@
 // Apache 2.0 license.
 package org.jetbrains.jewel.markdown.scrolling
 
+import androidx.compose.animation.core.AnimationSpec
+import androidx.compose.animation.core.SpringSpec
 import androidx.compose.foundation.ScrollState
 import androidx.compose.foundation.gestures.ScrollableState
 import androidx.compose.foundation.lazy.LazyListState
@@ -69,7 +71,7 @@ import org.jetbrains.jewel.markdown.processing.MarkdownProcessor
 @ExperimentalJewelApi
 public abstract class ScrollingSynchronizer {
     /** Scroll the preview to the position that match the given [sourceLine] the best. */
-    public abstract suspend fun scrollToLine(sourceLine: Int)
+    public abstract suspend fun scrollToLine(sourceLine: Int, animationSpec: AnimationSpec<Float> = SpringSpec())
 
     /**
      * Called when [MarkdownProcessor] processes the raw markdown text. The processing itself is passed as an [action].
@@ -146,7 +148,7 @@ public abstract class ScrollingSynchronizer {
         // so this map always keeps relevant information.
         private val blocks2TextOffsets = mutableMapOf<MarkdownBlock, List<Int>>()
 
-        override suspend fun scrollToLine(sourceLine: Int) {
+        override suspend fun scrollToLine(sourceLine: Int, animationSpec: AnimationSpec<Float>) {
             val block = findBestBlockForLine(sourceLine) ?: return
             val y = blocks2Top[block] ?: return
             if (y < 0) return
@@ -156,7 +158,7 @@ public abstract class ScrollingSynchronizer {
             // in this case scroll to the first line of the first block positioned after the line
             val lineIndexInBlock = maxOf(0, sourceLine - lineRange.start)
             val lineOffset = textOffsets?.get(lineIndexInBlock) ?: 0
-            scrollState.animateScrollTo(y + lineOffset)
+            scrollState.animateScrollTo(y + lineOffset, animationSpec)
         }
 
         private fun findBestBlockForLine(line: Int): MarkdownBlock? {

platform/jewel/markdown/core/src/test/kotlin/org/jetbrains/jewel/markdown/scrolling/ScrollingSynchronizerTest.kt

@@ -21,6 +21,7 @@ import androidx.compose.ui.text.style.TextAlign
 import androidx.compose.ui.unit.Density
 import androidx.compose.ui.unit.dp
 import androidx.compose.ui.unit.sp
+import java.util.Arrays
 import kotlin.time.Duration.Companion.milliseconds
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.launch
@@ -59,7 +60,6 @@ import org.jetbrains.jewel.ui.component.styling.TrackClickBehavior
 import org.junit.Assert.assertEquals
 import org.junit.Assert.assertTrue
 import org.junit.Test
-import java.util.Arrays
 
 @Suppress("LargeClass")
 class ScrollingSynchronizerTest {

plugins/markdown/compose/src/main/kotlin/com/intellij/markdown/compose/preview/MarkdownComposePanel.kt

@@ -1,6 +1,9 @@
 // Copyright 2000-2025 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
 package com.intellij.markdown.compose.preview
 
+import androidx.compose.animation.core.AnimationSpec
+import androidx.compose.animation.core.LinearEasing
+import androidx.compose.animation.core.TweenSpec
 import androidx.compose.foundation.*
 import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.fillMaxWidth
@@ -95,7 +98,11 @@ internal class MarkdownComposePanel(
   @OptIn(FlowPreview::class)
   @Suppress("FunctionName")
   @Composable
-  private fun MarkdownPreviewPanel(scrollState: ScrollState, scrollingSynchronizer: ScrollingSynchronizer?, blockRenderer: ScrollSyncMarkdownBlockRenderer) {
+  private fun MarkdownPreviewPanel(scrollState: ScrollState,
+                                   scrollingSynchronizer: ScrollingSynchronizer?,
+                                   blockRenderer: ScrollSyncMarkdownBlockRenderer,
+                                   animationSpec: AnimationSpec<Float> = TweenSpec(easing = LinearEasing)
+  ) {
     val request by updateHandler.requests.collectAsState(null)
     (request as? PreviewRequest.Update)?.let {
       if (scrollingSynchronizer != null) {
@@ -103,7 +110,7 @@ internal class MarkdownComposePanel(
         LaunchedEffect(Unit) {
           coroutineScope.launch {
             scrollToLineFlow.debounce(16.milliseconds).collect { scrollToLine ->
-              scrollingSynchronizer.scrollToLine(scrollToLine)
+              scrollingSynchronizer.scrollToLine(scrollToLine, animationSpec)
             }
           }
         }