Extract the Skiko text backend into the ui-skiko module

Move the Skia-backed implementation of ui-text into ui-skiko, leaving
ui-text's nonAndroidMain Skia-free, mirroring the graphics extraction.
ui-text keeps expect/actual delegators resolving a registered
ComposeUiTextImplementation; the org.jetbrains.skia paragraph, font and
text-paint code lives in ui-skiko.

- Paragraph building, intrinsics, char helpers and the font subsystem
  (FontFamilyResolver, font loading, PlatformFont) relocate to ui-skiko.
- The font subsystem is ui-text's own public API with per-platform
  loadTypeface actuals, so the unavoidable public Skia-typed surface
  stays in ui-text's skikoMain compat layer (Skia-free nonAndroidMain ->
  Skia skikoMain -> platform leaves); only the implementation moves.
- ComposeUiSkikoRuntime.registerSkikoComposeImplementation() now wires
  both the graphics and text implementations (plus the temporary
  SkikoGraphicsCompat bridge).

API baselines are regenerated in a later commit.

Author: MatkovIvan

…roidx/compose/ui/text/CharHelpers.jvm.kt …roidx/compose/ui/text/CharHelpers.jvm.ktcompose/ui/ui-text/src/desktopMain/kotlin/androidx/compose/ui/text/CharHelpers.jvm.kt renamed to compose/ui/ui-skiko/src/desktopMain/kotlin/androidx/compose/ui/text/CharHelpers.jvm.kt compose/ui/ui-text/src/desktopMain/kotlin/androidx/compose/ui/text/CharHelpers.jvm.kt renamed to compose/ui/ui-skiko/src/desktopMain/kotlin/androidx/compose/ui/text/CharHelpers.jvm.kt

@@ -15,11 +15,6 @@
  */
 package androidx.compose.ui.text
 
-
-/**
- * Get strong (R, L or AL) direction type.
- * See https://www.unicode.org/reports/tr9/
- */
 internal actual fun CodePoint.strongDirectionType(): StrongDirectionType =
     when (getDirectionality()) {
         CharDirectionality.LEFT_TO_RIGHT -> StrongDirectionType.Ltr
@@ -29,6 +24,7 @@ internal actual fun CodePoint.strongDirectionType(): StrongDirectionType =
 
         else -> StrongDirectionType.None
     }
+
 internal actual fun CodePoint.isNeutralDirection(): Boolean =
     when (getDirectionality()) {
         CharDirectionality.OTHER_NEUTRALS,
@@ -41,8 +37,5 @@ internal actual fun CodePoint.isNeutralDirection(): Boolean =
 internal actual fun CodePoint.isNonSpacingMark(): Boolean =
     getDirectionality() == CharDirectionality.NONSPACING_MARK
 
-/**
- * Get the Unicode directionality of a character.
- */
 private fun CodePoint.getDirectionality(): CharDirectionality =
     CharDirectionality.valueOf(Character.getDirectionality(this).toInt())

…xt/platform/ParagraphLayouter.desktop.kt …xt/platform/ParagraphLayouter.desktop.ktcompose/ui/ui-text/src/desktopMain/kotlin/androidx/compose/ui/text/platform/ParagraphLayouter.desktop.kt renamed to compose/ui/ui-skiko/src/desktopMain/kotlin/androidx/compose/ui/text/platform/ParagraphLayouter.desktop.kt compose/ui/ui-text/src/desktopMain/kotlin/androidx/compose/ui/text/platform/ParagraphLayouter.desktop.kt renamed to compose/ui/ui-skiko/src/desktopMain/kotlin/androidx/compose/ui/text/platform/ParagraphLayouter.desktop.kt

@@ -0,0 +1,48 @@
+/*
+ * Copyright 2026 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package androidx.compose.ui.platform
+
+import androidx.compose.ui.InternalComposeUiApi
+import androidx.compose.ui.graphics.ComposeUiGraphicsImplementationRegistry
+import androidx.compose.ui.graphics.PlatformRenderEffect
+import androidx.compose.ui.graphics.SkikoGraphicsCompat
+import androidx.compose.ui.graphics.SkikoGraphicsCompatRegistry
+import androidx.compose.ui.graphics.SkikoGraphicsImplementation
+import androidx.compose.ui.graphics.skiaImageFilter
+import androidx.compose.ui.text.ComposeUiTextImplementationRegistry
+import androidx.compose.ui.text.SkikoTextImplementation
+import org.jetbrains.skia.ImageFilter
+
+@OptIn(InternalComposeUiApi::class)
+@Suppress("DEPRECATION")
+@InternalComposeUiApi
+fun registerSkikoComposeImplementation() {
+    ComposeUiGraphicsImplementationRegistry.register(SkikoGraphicsImplementation)
+    ComposeUiTextImplementationRegistry.register(SkikoTextImplementation)
+    SkikoGraphicsCompatRegistry.register(SkikoGraphicsCompatImpl)
+}
+
+/**
+ * Temporary bridge backing the deprecated Skia-returning members that cannot be relocated to this
+ * module (see [SkikoGraphicsCompat]). Delegates to the proper `skiaImageFilter` extension.
+ */
+@OptIn(InternalComposeUiApi::class)
+@Suppress("DEPRECATION")
+private object SkikoGraphicsCompatImpl : SkikoGraphicsCompat {
+    override fun imageFilter(renderEffect: PlatformRenderEffect): ImageFilter =
+        renderEffect.skiaImageFilter
+}

…ext/platform/ParagraphLayouter.native.kt …ext/platform/ParagraphLayouter.native.ktcompose/ui/ui-text/src/nativeMain/kotlin/androidx/compose/ui/text/platform/ParagraphLayouter.native.kt renamed to compose/ui/ui-skiko/src/nativeMain/kotlin/androidx/compose/ui/text/platform/ParagraphLayouter.native.kt compose/ui/ui-text/src/nativeMain/kotlin/androidx/compose/ui/text/platform/ParagraphLayouter.native.kt renamed to compose/ui/ui-skiko/src/nativeMain/kotlin/androidx/compose/ui/text/platform/ParagraphLayouter.native.kt

@@ -0,0 +1,30 @@
+/*
+ * Copyright 2026 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+@file:OptIn(InternalComposeUiApi::class)
+
+package androidx.compose.ui.text
+
+import androidx.compose.ui.InternalComposeUiApi
+import org.jetbrains.skia.Font as SkFont
+
+/**
+ * Access to the default Skia font behind a paragraph implementation. Kept here (in :ui-skiko) so the
+ * skia type does not leak back into the skia-free ui-text `nonAndroidMain`. Primarily for tests.
+ */
+@InternalComposeUiApi
+val ComposeUiParagraphImplementation.skiaDefaultFont: SkFont
+    get() = (this as PlatformParagraphImpl).defaultFont

compose/ui/ui-skiko/src/nonAndroidMain/kotlin/androidx/compose/ui/platform/ComposeUiSkikoRuntime.nonAndroid.kt

@@ -14,9 +14,12 @@
  * limitations under the License.
  */
 
+@file:OptIn(InternalComposeUiApi::class)
+
 package androidx.compose.ui.text
 
 import org.jetbrains.skia.Rect as SkRect
+import androidx.compose.ui.InternalComposeUiApi
 import androidx.compose.ui.geometry.Offset
 import androidx.compose.ui.geometry.Rect
 import androidx.compose.ui.geometry.Size
@@ -30,8 +33,8 @@ import androidx.compose.ui.graphics.asComposePath
 import androidx.compose.ui.graphics.drawscope.DrawStyle
 import androidx.compose.ui.graphics.skiaCanvas
 import androidx.compose.ui.graphics.toComposeRect
-import androidx.compose.ui.text.internal.requirePrecondition
-import androidx.compose.ui.text.platform.SkiaParagraphIntrinsics
+import androidx.compose.ui.text.platform.PlatformParagraphIntrinsicsImpl
+import androidx.compose.ui.text.platform.requireParagraphPrecondition
 import androidx.compose.ui.text.platform.cursorHorizontalPosition
 import androidx.compose.ui.text.style.LineHeightStyle
 import androidx.compose.ui.text.style.ResolvedTextDirection
@@ -51,12 +54,12 @@ import org.jetbrains.skia.paragraph.RectWidthMode
 import org.jetbrains.skia.paragraph.TextBox
 import org.jetbrains.skia.paragraph.Paragraph as SkParagraph
 
-internal class SkiaParagraph(
-    private val paragraphIntrinsics: SkiaParagraphIntrinsics,
+internal class PlatformParagraphImpl(
+    private val paragraphIntrinsics: PlatformParagraphIntrinsicsImpl,
     val maxLines: Int,
     private val overflow: TextOverflow,
     val constraints: Constraints
-) : Paragraph {
+) : ComposeUiParagraphImplementation {
     private val layouter = paragraphIntrinsics.layouter().apply {
         setParagraphStyle(maxLines, ellipsis)
     }
@@ -77,11 +80,11 @@ internal class SkiaParagraph(
         }
 
     init {
-        requirePrecondition(constraints.minHeight == 0 && constraints.minWidth == 0) {
+        requireParagraphPrecondition(constraints.minHeight == 0 && constraints.minWidth == 0) {
             "Setting Constraints.minWidth and Constraints.minHeight is not supported, " +
                 "these should be the default zero values instead."
         }
-        requirePrecondition(maxLines >= 1) { "maxLines should be greater than 0" }
+        requireParagraphPrecondition(maxLines >= 1) { "maxLines should be greater than 0" }
 
         // Size is not known until layout is complete but to apply it, we need to re-create
         // skia's paragraph :'(
@@ -160,7 +163,7 @@ internal class SkiaParagraph(
             }
 
     override fun getPathForRange(start: Int, end: Int): Path {
-        requirePrecondition(start in 0..end && end <= text.length) {
+        requireParagraphPrecondition(start in 0..end && end <= text.length) {
             "start($start) or end($end) is out of range [0..${text.length}]," +
                 " or start > end!"
         }
@@ -184,7 +187,7 @@ internal class SkiaParagraph(
         val line = lineMetricsForOffset(offset)!!
 
         // workaround for https://bugs.chromium.org/p/skia/issues/detail?id=11321 :(
-        // Otherwise it shows a big cursor on a new empty line https://youtrack.jetbrains.com/issue/CMP-1895
+        // Otherwise it shows a big cursor on a new empty line https://github.com/JetBrains/compose-jb/issues/1895
         val isNewEmptyLine = offset - 1 == line.startIndex && offset == text.length
         val metrics = defaultFont.metrics
 
@@ -229,13 +232,13 @@ internal class SkiaParagraph(
             floor((line.baseline + line.descent).toFloat())
         } ?: 0f
 
-    internal fun getLineAscent(lineIndex: Int): Float =
+    override fun getLineAscent(lineIndex: Int): Float =
         -(lineMetrics.getOrNull(lineIndex)?.ascent?.toFloat() ?: 0f)
 
     override fun getLineBaseline(lineIndex: Int): Float =
         lineMetrics.getOrNull(lineIndex)?.baseline?.toFloat() ?: 0f
 
-    internal fun getLineDescent(lineIndex: Int): Float =
+    override fun getLineDescent(lineIndex: Int): Float =
         lineMetrics.getOrNull(lineIndex)?.descent?.toFloat() ?: 0f
 
     private fun lineMetricsForOffset(offset: Int): LineMetrics? =
@@ -440,8 +443,8 @@ internal class SkiaParagraph(
 
             if (isNonSpacingMark) {
                 // Find the boundaries of the complex character
-                val precedingBreak = text.findPrecedingBreak(glyphPosition)
-                val followingBreak = text.findFollowingBreak(glyphPosition)
+                val precedingBreak = findSkikoPrecedingBreak(text, glyphPosition)
+                val followingBreak = findSkikoFollowingBreak(text, glyphPosition)
 
                 // If we're inside a complex character, jump to the end of it
                 if (precedingBreak != glyphPosition && followingBreak != glyphPosition) {
@@ -541,7 +544,7 @@ internal class SkiaParagraph(
     }
 
     override fun getBoundingBox(offset: Int): Rect {
-        requirePrecondition(offset in text.indices) {
+        requireParagraphPrecondition(offset in text.indices) {
             "offset($offset) is out of bounds [0,${text.length})"
         }
         val box = getBoxForwardByOffset(offset) ?: getBoxBackwardByOffset(offset, text.length)!!
@@ -661,7 +664,7 @@ internal class SkiaParagraph(
      */
     @Suppress("NOTHING_TO_INLINE")
     private inline fun checkOffsetIsValid(offset: Int) {
-        requirePrecondition(offset in 0..text.length) {
+        requireParagraphPrecondition(offset in 0..text.length) {
             "offset($offset) is out of bounds [0,${text.length}]"
         }
     }
@@ -673,6 +676,7 @@ private fun LineMetrics.trimFirstAscent(
 ): LineMetrics {
     if (textStyle.lineHeight.isUnspecified) return this
     val style = textStyle.lineHeightStyle ?: LineHeightStyle.Default
+    @Suppress("INVISIBLE_REFERENCE") // FIXME: Make [isTrimFirstLineTop] public
     val ascent = if (style.trim.isTrimFirstLineTop()) {
         -fontMetrics.ascent.toDouble()
     } else {
@@ -687,6 +691,7 @@ private fun LineMetrics.trimLastDescent(
 ): LineMetrics {
     if (textStyle.lineHeight.isUnspecified) return this
     val style = textStyle.lineHeightStyle ?: LineHeightStyle.Default
+    @Suppress("INVISIBLE_REFERENCE") // FIXME: Make [isTrimLastLineBottom] public
     val descent = if (style.trim.isTrimLastLineBottom()) {
         fontMetrics.descent.toDouble()
     } else {
@@ -725,7 +730,7 @@ private fun LineMetrics.copy(
     lineNumber = lineNumber
 )
 
-private fun Paragraph.numberOfLinesThatFitMaxHeight(maxHeight: Int): Int {
+private fun PlatformParagraphImpl.numberOfLinesThatFitMaxHeight(maxHeight: Int): Int {
     for (lineIndex in 0 until lineCount) {
         if (getLineBottom(lineIndex) > maxHeight) return lineIndex
     }

compose/ui/ui-skiko/src/nonAndroidMain/kotlin/androidx/compose/ui/text/ParagraphDefaultFontAccess.nonAndroid.kt

@@ -20,16 +20,16 @@ import kotlin.experimental.ExperimentalNativeApi
 import kotlin.jvm.JvmInline
 import org.jetbrains.skia.BreakIterator
 
-internal actual fun String.findPrecedingBreak(index: Int): Int {
-    val it = BreakIterator.makeCharacterInstance()
-    it.setText(this)
-    return it.preceding(index)
+internal fun findSkikoPrecedingBreak(text: String, index: Int): Int {
+    val iterator = BreakIterator.makeCharacterInstance()
+    iterator.setText(text)
+    return iterator.preceding(index)
 }
 
-internal actual fun String.findFollowingBreak(index: Int): Int {
-    val it = BreakIterator.makeCharacterInstance()
-    it.setText(this)
-    return it.following(index)
+internal fun findSkikoFollowingBreak(text: String, index: Int): Int {
+    val iterator = BreakIterator.makeCharacterInstance()
+    iterator.setText(text)
+    return iterator.following(index)
 }
 
 /**
@@ -44,42 +44,24 @@ internal value class StrongDirectionType private constructor(val value: Int) {
     }
 }
 
-// TODO Remove once it's available in common stdlib https://youtrack.jetbrains.com/issue/KT-23251
 internal typealias CodePoint = Int
 
-/**
- * Converts a surrogate pair to a unicode code point.
- */
 @OptIn(ExperimentalNativeApi::class)
 private fun Char.Companion.toCodePoint(high: Char, low: Char): CodePoint =
     (((high - MIN_HIGH_SURROGATE) shl 10) or (low - MIN_LOW_SURROGATE)) + MIN_SUPPLEMENTARY_CODE_POINT
 
-/**
- * The minimum value of a supplementary code point, `\u0x10000`.
- */
 private const val MIN_SUPPLEMENTARY_CODE_POINT: Int = 0x10000
-
-/**
- * The maximum value of a Unicode code point.
- */
 private const val MAX_CODE_POINT = 0X10FFFF
 
 internal fun CodePoint.charCount(): Int = if (this >= MIN_SUPPLEMENTARY_CODE_POINT) 2 else 1
 
-/**
- * Checks if the codepoint specified is a supplementary codepoint or not.
- */
 internal fun CodePoint.isSupplementaryCodePoint(): Boolean =
     this in MIN_SUPPLEMENTARY_CODE_POINT..MAX_CODE_POINT
 
 internal expect fun CodePoint.strongDirectionType(): StrongDirectionType
 internal expect fun CodePoint.isNeutralDirection(): Boolean
 internal expect fun CodePoint.isNonSpacingMark(): Boolean
 
-/**
- * Determine direction based on the first strong directional character.
- * Only considers the characters outside isolate pairs.
- */
 internal fun CharSequence.firstStrongDirectionType(): StrongDirectionType {
     for (codePoint in codePointsOutsideDirectionalIsolate) {
         return when (val strongDirectionType = codePoint.strongDirectionType()) {
@@ -90,16 +72,7 @@ internal fun CharSequence.firstStrongDirectionType(): StrongDirectionType {
     return StrongDirectionType.None
 }
 
-/**
- * U+2066 LEFT-TO-RIGHT ISOLATE (LRI)
- * U+2067 RIGHT-TO-LEFT ISOLATE (RLI)
- * U+2068 FIRST STRONG ISOLATE (FSI)
- */
 private val PUSH_DIRECTIONAL_ISOLATE_RANGE: IntRange = 0x2066..0x2068
-
-/**
- * U+2069 POP DIRECTIONAL ISOLATE (PDI)
- */
 private const val POP_DIRECTIONAL_ISOLATE_CODE_POINT: Int = 0x2069
 
 private val CharSequence.codePointsOutsideDirectionalIsolate get() = sequence {
@@ -126,9 +99,6 @@ internal val CharSequence.codePoints get() = sequence {
     }
 }
 
-/**
- * Returns the character (Unicode code point) at the specified index.
- */
 internal fun CharSequence.codePointAt(index: Int): CodePoint {
     val high = this[index]
     if (high.isHighSurrogate() && index + 1 < this.length) {
@@ -140,9 +110,6 @@ internal fun CharSequence.codePointAt(index: Int): CodePoint {
     return high.code
 }
 
-/**
- * Returns the character (Unicode code point) before the specified index.
- */
 internal fun CharSequence.codePointBefore(index: Int): CodePoint {
     val low = this[index]
     if (low.isLowSurrogate() && index - 1 >= 0) {