Fix initial cursor position in empty TextField when TextAlignment is …

…set explicitly (#1354)

After focusing on the textfield and before entering any text, now
blinking cursor will be positioned in accordance with TextAlignment.

Fixes https://youtrack.jetbrains.com/issue/COMPOSE-1360/
Fixes JetBrains/compose-multiplatform#2711
Fixes JetBrains/compose-multiplatform#3098
Fixes JetBrains/compose-multiplatform#4611

## Testing
Manual testing.

## Release Notes
<!--
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Sections:
- Highlights
- Known issues
- Breaking changes
- Features
- Fixes

Subsections:
- Multiple Platforms
- iOS
- Desktop
- Web
- Resources
- Gradle Plugin
-->
### Fixes - Multiple Platforms
- Fix initial cursor position in the empty `TextField` with explicitly
set `TextAlignment`.

## Google CLA
You need to sign the Google Contributor’s License Agreement at
https://cla.developers.google.com/.
This is needed since we synchronise most of the code with Google’s AOSP
repository. Signing this agreement allows us to synchronise code from
your Pull Requests as well.

---------

Co-authored-by: Ivan Matkov <ivan.matkov@jetbrains.com>

compose/ui/ui-text/src/skikoMain/kotlin/androidx/compose/ui/text/SkiaParagraph.skiko.kt

@@ -34,6 +34,7 @@ import androidx.compose.ui.text.platform.SkiaParagraphIntrinsics
 import androidx.compose.ui.text.platform.cursorHorizontalPosition
 import androidx.compose.ui.text.style.LineHeightStyle
 import androidx.compose.ui.text.style.ResolvedTextDirection
+import androidx.compose.ui.text.style.TextAlign
 import androidx.compose.ui.text.style.TextDecoration
 import androidx.compose.ui.unit.Constraints
 import androidx.compose.ui.unit.isUnspecified
@@ -256,7 +257,7 @@ internal class SkiaParagraph(
         val isRtl = paragraphIntrinsics.textDirection == ResolvedTextDirection.Rtl
         val isLtr = !isRtl
         return when {
-            prevBox == null && nextBox == null -> if (isRtl) width else 0f
+            prevBox == null && nextBox == null -> getAlignedStartingPosition(isRtl)
             prevBox == null -> nextBox!!.cursorHorizontalPosition(true)
             nextBox == null -> prevBox.cursorHorizontalPosition()
             nextBox.direction == prevBox.direction -> nextBox.cursorHorizontalPosition(true)
@@ -269,6 +270,16 @@ internal class SkiaParagraph(
         }
     }
 
+    private fun getAlignedStartingPosition(isRtl: Boolean): Float =
+        when (layouter.textStyle.textAlign) {
+            TextAlign.Left -> 0f
+            TextAlign.Right -> width
+            TextAlign.Center -> width / 2
+            TextAlign.Start -> if (isRtl) width else 0f
+            TextAlign.End -> if (isRtl) 0f else width
+            else -> 0f
+        }
+
     private var _lineMetrics: Array<LineMetrics>? = null
     private val lineMetrics: Array<LineMetrics>
         get() {

compose/ui/ui-text/src/skikoTest/kotlin/androidx/compose/ui/text/SkikoParagraphTest.kt

@@ -17,6 +17,8 @@
 package androidx.compose.ui.text
 
 import androidx.compose.ui.text.font.createFontFamilyResolver
+import androidx.compose.ui.text.style.TextAlign
+import androidx.compose.ui.text.style.TextDirection
 import androidx.compose.ui.unit.Constraints
 import androidx.compose.ui.unit.Density
 import kotlin.test.Ignore
@@ -28,6 +30,7 @@ import kotlin.test.assertFailsWith
 class SkikoParagraphTest {
     private val fontFamilyResolver = createFontFamilyResolver()
     private val defaultDensity = Density(density = 1f)
+    private val maxWidthConstraint = 1000
 
     @Test
     fun getWordBoundary_out_of_boundary_too_small() {
@@ -315,7 +318,8 @@ class SkikoParagraphTest {
     fun getWordBoundary_multichar() {
         // "ab 𐐔𐐯𐑅𐐨𐑉𐐯𐐻 cd" - example of multi-char code units
         //             | (offset=3)      | (offset=6)
-        val text = "ab \uD801\uDC14\uD801\uDC2F\uD801\uDC45\uD801\uDC28\uD801\uDC49\uD801\uDC2F\uD801\uDC3B cd"
+        val text =
+            "ab \uD801\uDC14\uD801\uDC2F\uD801\uDC45\uD801\uDC28\uD801\uDC49\uD801\uDC2F\uD801\uDC3B cd"
         val paragraph = simpleParagraph(text)
 
         assertEquals(
@@ -324,10 +328,60 @@ class SkikoParagraphTest {
         )
     }
 
-    private fun simpleParagraph(text: String) = Paragraph(
+    @Test
+    fun getHorizontalPosition_cursor_empty_textfield_ltr_start_alignment() {
+        val paragraph = simpleParagraph("", TextStyle(textAlign = TextAlign.Start, textDirection = TextDirection.Ltr))
+        val cursorHorizontalPosition: Float = paragraph.getHorizontalPosition(0, false)
+        assertEquals(0f, cursorHorizontalPosition)
+    }
+
+    @Test
+    fun getHorizontalPosition_cursor_empty_textfield_ltr_end_alignment() {
+        val paragraph = simpleParagraph("", TextStyle(textAlign = TextAlign.End, textDirection = TextDirection.Ltr))
+        val cursorHorizontalPosition = paragraph.getHorizontalPosition(0, false)
+        assertEquals(maxWidthConstraint.toFloat(), cursorHorizontalPosition)
+    }
+
+    @Test
+    fun getHorizontalPosition_cursor_empty_textfield_center_alignment() {
+        val paragraph = simpleParagraph("", TextStyle(textAlign = TextAlign.Center))
+        val cursorHorizontalPosition = paragraph.getHorizontalPosition(0, false)
+        assertEquals((maxWidthConstraint / 2).toFloat(), cursorHorizontalPosition)
+    }
+
+    @Test
+    fun getHorizontalPosition_cursor_empty_textfield_rtl_start_alignment() {
+        val paragraph = simpleParagraph("", TextStyle(textAlign = TextAlign.Start, textDirection = TextDirection.Rtl))
+        val cursorHorizontalPosition: Float = paragraph.getHorizontalPosition(0, false)
+        assertEquals(maxWidthConstraint.toFloat(), cursorHorizontalPosition)
+    }
+
+    @Test
+    fun getHorizontalPosition_cursor_empty_textfield_rtl_end_alignment() {
+        val paragraph = simpleParagraph("", TextStyle(textAlign = TextAlign.End, textDirection = TextDirection.Rtl))
+        val cursorHorizontalPosition = paragraph.getHorizontalPosition(0, false)
+        assertEquals(0f, cursorHorizontalPosition)
+    }
+
+    @Test
+    fun getHorizontalPosition_cursor_empty_textfield_left_alignment() {
+        val paragraph = simpleParagraph("", TextStyle(textAlign = TextAlign.Start))
+        val cursorHorizontalPosition: Float = paragraph.getHorizontalPosition(0, false)
+        assertEquals(0f, cursorHorizontalPosition)
+    }
+
+    @Test
+    fun getHorizontalPosition_cursor_empty_textfield_right_alignment() {
+        val paragraph = simpleParagraph("", TextStyle(textAlign = TextAlign.End))
+        val cursorHorizontalPosition = paragraph.getHorizontalPosition(0, false)
+        assertEquals(maxWidthConstraint.toFloat(), cursorHorizontalPosition)
+    }
+
+
+    private fun simpleParagraph(text: String, textStyle: TextStyle = TextStyle()) = Paragraph(
         text = text,
-        style = TextStyle(),
-        constraints = Constraints(maxWidth = 1000),
+        style = textStyle,
+        constraints = Constraints(maxWidth = maxWidthConstraint),
         density = defaultDensity,
         fontFamilyResolver = fontFamilyResolver
     )