feat: support for textVariableAnchorOffset (does not work yet) (#149)

lib/maplibre-compose/src/androidMain/kotlin/dev/sargunv/maplibrecompose/core/layer/SymbolLayer.kt

@@ -23,6 +23,7 @@ import dev.sargunv.maplibrecompose.core.expression.TextJustify
 import dev.sargunv.maplibrecompose.core.expression.TextPitchAlignment
 import dev.sargunv.maplibrecompose.core.expression.TextRotationAlignment
 import dev.sargunv.maplibrecompose.core.expression.TextTransform
+import dev.sargunv.maplibrecompose.core.expression.TextVariableAnchorOffsetValue
 import dev.sargunv.maplibrecompose.core.expression.TextWritingMode
 import dev.sargunv.maplibrecompose.core.expression.TranslateAnchor
 import dev.sargunv.maplibrecompose.core.source.Source
@@ -198,7 +199,9 @@ internal actual class SymbolLayer actual constructor(id: String, source: Source)
     impl.setProperties(PropertyFactory.textVariableAnchor(variableAnchor.toMLNExpression()))
   }
 
-  actual fun setTextVariableAnchorOffset(variableAnchorOffset: Expression<ListValue<*>>) {
+  actual fun setTextVariableAnchorOffset(
+    variableAnchorOffset: Expression<TextVariableAnchorOffsetValue>
+  ) {
     impl.setProperties(
       PropertyFactory.textVariableAnchorOffset(variableAnchorOffset.toMLNExpression())
     )

lib/maplibre-compose/src/commonMain/kotlin/dev/sargunv/maplibrecompose/compose/layer/SymbolLayer.kt

@@ -41,6 +41,7 @@ import dev.sargunv.maplibrecompose.core.expression.TextPitchAlignment
 import dev.sargunv.maplibrecompose.core.expression.TextRotationAlignment
 import dev.sargunv.maplibrecompose.core.expression.TextTransform
 import dev.sargunv.maplibrecompose.core.expression.TextUnitValue
+import dev.sargunv.maplibrecompose.core.expression.TextVariableAnchorOffsetValue
 import dev.sargunv.maplibrecompose.core.expression.TextWritingMode
 import dev.sargunv.maplibrecompose.core.expression.TranslateAnchor
 import dev.sargunv.maplibrecompose.core.expression.ZeroPadding
@@ -452,7 +453,7 @@ public fun SymbolLayer(
   textOffset: Expression<TextOffsetValue> = textOffset(0f.em, 0f.em),
   textVariableAnchor: Expression<ListValue<EnumValue<SymbolAnchor>>> = nil(),
   textRadialOffset: Expression<TextUnitValue> = const(0f.em),
-  textVariableAnchorOffset: Expression<ListValue<*>> = nil(), // TODO proper type
+  textVariableAnchorOffset: Expression<TextVariableAnchorOffsetValue> = nil(),
 
   // text collision
   textPadding: Expression<DpValue> = const(2.dp),

lib/maplibre-compose/src/commonMain/kotlin/dev/sargunv/maplibrecompose/core/expression/ExpressionValue.kt

@@ -83,16 +83,31 @@ public sealed interface ColorValue : ExpressionValue, InterpolateableValue<Color
 
 /**
  * Represents an [Expression] that resolves to a map value (corresponds to a JSON object). See
- * [ExpressionsDsl.literal].
+ * [ExpressionsDsl.const].
  */
 public sealed interface MapValue<out T : ExpressionValue> : ExpressionValue
 
 /**
  * Represents an [Expression] that resolves to a list value (corresponds to a JSON array). See
- * [ExpressionsDsl.literal].
+ * [ExpressionsDsl.const].
  */
 public sealed interface ListValue<out T : ExpressionValue> : ExpressionValue
 
+/**
+ * Represents an [Expression] that resolves to a list value (corresponds to a JSON array) of
+ * alternating types.
+ */
+public sealed interface TupleListValue<out T1 : ExpressionValue, out T2 : ExpressionValue> :
+  ListValue<ExpressionValue>
+
+/**
+ * Represents an [Expression] that resolves to an alternating list of [SymbolAnchor] and
+ * [OffsetValue].
+ *
+ * See [SymbolLayer][dev.sargunv.maplibrecompose.compose.layer.SymbolLayer].
+ */
+public typealias TextVariableAnchorOffsetValue = TupleListValue<SymbolAnchor, OffsetValue>
+
 /**
  * Represents an [Expression] that resolves to a list of numbers.
  *

lib/maplibre-compose/src/commonMain/kotlin/dev/sargunv/maplibrecompose/core/expression/ExpressionsDsl.kt

@@ -70,16 +70,40 @@ public object ExpressionsDsl {
   public fun const(padding: PaddingValues.Absolute): Expression<PaddingValue> =
     Expression.ofPadding(padding)
 
+  internal fun literal(list: List<Any?>): Expression<ListValue<*>> =
+    Expression.ofList(listOf("literal", list)).cast()
+
   /** Creates a literal expression for a list of strings. */
   @JvmName("constStringList")
-  public fun const(list: List<String>): Expression<ListValue<StringValue>> =
-    Expression.ofList(listOf("literal", list)).cast()
+  public fun const(list: List<String>): Expression<ListValue<StringValue>> = literal(list).cast()
 
   /** Creates a literal expression for a list of numbers. */
   @JvmName("constNumberList")
-  public fun const(list: List<Number>): Expression<VectorValue<FloatValue>> =
-    Expression.ofList(listOf("literal", list)).cast()
+  public fun const(list: List<Number>): Expression<VectorValue<FloatValue>> = literal(list).cast()
+
+  /**
+   * Creates a literal expression for [TextVariableAnchorOffsetValue], used by
+   * [SymbolLayer][dev.sargunv.maplibrecompose.compose.layer.SymbolLayer]'s
+   * `textVariableAnchorOffset` parameter.
+   *
+   * The offset is measured in a multipler of the text size (EM). It's in [Offset] instead of
+   * [textOffset] because of technical limitations in MapLibre.
+   */
+  public fun textVariableAnchorOffset(
+    vararg pairs: Pair<SymbolAnchor, Offset>
+  ): Expression<TextVariableAnchorOffsetValue> {
+    return literal(
+        buildList {
+          pairs.forEach { (anchor, offset) ->
+            add(anchor.stringConst)
+            add(offset)
+          }
+        }
+      )
+      .cast()
+  }
 
+  /** Creates a literal expression for 2D [TextUnit] offset. */
   public fun textOffset(x: TextUnit, y: TextUnit): Expression<TextOffsetValue> {
     require(x.type == y.type) { "x and y must have the same TextUnitType" }
 

lib/maplibre-compose/src/commonMain/kotlin/dev/sargunv/maplibrecompose/core/layer/SymbolLayer.kt

@@ -23,6 +23,7 @@ import dev.sargunv.maplibrecompose.core.expression.TextJustify
 import dev.sargunv.maplibrecompose.core.expression.TextPitchAlignment
 import dev.sargunv.maplibrecompose.core.expression.TextRotationAlignment
 import dev.sargunv.maplibrecompose.core.expression.TextTransform
+import dev.sargunv.maplibrecompose.core.expression.TextVariableAnchorOffsetValue
 import dev.sargunv.maplibrecompose.core.expression.TextWritingMode
 import dev.sargunv.maplibrecompose.core.expression.TranslateAnchor
 import dev.sargunv.maplibrecompose.core.source.Source
@@ -109,7 +110,7 @@ internal expect class SymbolLayer(id: String, source: Source) : FeatureLayer {
 
   fun setTextVariableAnchor(variableAnchor: Expression<ListValue<EnumValue<SymbolAnchor>>>)
 
-  @JsOnlyApi fun setTextVariableAnchorOffset(variableAnchorOffset: Expression<ListValue<*>>)
+  fun setTextVariableAnchorOffset(variableAnchorOffset: Expression<TextVariableAnchorOffsetValue>)
 
   fun setTextAnchor(anchor: Expression<EnumValue<SymbolAnchor>>)
 

lib/maplibre-compose/src/iosMain/kotlin/dev/sargunv/maplibrecompose/core/layer/SymbolLayer.kt

@@ -24,6 +24,7 @@ import dev.sargunv.maplibrecompose.core.expression.TextJustify
 import dev.sargunv.maplibrecompose.core.expression.TextPitchAlignment
 import dev.sargunv.maplibrecompose.core.expression.TextRotationAlignment
 import dev.sargunv.maplibrecompose.core.expression.TextTransform
+import dev.sargunv.maplibrecompose.core.expression.TextVariableAnchorOffsetValue
 import dev.sargunv.maplibrecompose.core.expression.TextWritingMode
 import dev.sargunv.maplibrecompose.core.expression.TranslateAnchor
 import dev.sargunv.maplibrecompose.core.source.Source
@@ -203,7 +204,9 @@ internal actual class SymbolLayer actual constructor(id: String, source: Source)
     impl.textVariableAnchor = variableAnchor.toNSExpression()
   }
 
-  actual fun setTextVariableAnchorOffset(variableAnchorOffset: Expression<ListValue<*>>) {
+  actual fun setTextVariableAnchorOffset(
+    variableAnchorOffset: Expression<TextVariableAnchorOffsetValue>
+  ) {
     impl.textVariableAnchorOffset = variableAnchorOffset.toNSExpression()
   }