demo/src/jvmMain/kotlin/Main.kt

@@ -12,6 +12,7 @@ import androidx.compose.ui.window.application
 import centre.sciprog.maps.GeodeticMapCoordinates
 import centre.sciprog.maps.MapViewPoint
 import centre.sciprog.maps.compose.*
+import centre.sciprog.maps.toDegrees
 import io.ktor.client.HttpClient
 import io.ktor.client.engine.cio.CIO
 import kotlinx.coroutines.delay
@@ -47,18 +48,27 @@ fun App() {
 
         var centerCoordinates by remember { mutableStateOf<GeodeticMapCoordinates?>(null) }
 
+        val pointOne = 55.568548 to 37.568604
+        var pointTwo by remember { mutableStateOf(55.929444 to 37.518434) }
+        val pointThree = 60.929444 to 37.518434
 
         MapView(
             mapTileProvider = mapTileProvider,
             initialViewPoint = viewPoint,
             config = MapViewConfig(
                 inferViewBoxFromFeatures = true,
-                onViewChange = { centerCoordinates = focus }
+                onViewChange = { centerCoordinates = focus },
+                onDrag = { start, end ->
+                    if (start.focus.latitude.toDegrees() in (pointTwo.first - 0.05)..(pointTwo.first + 0.05) &&
+                        start.focus.longitude.toDegrees() in (pointTwo.second - 0.05)..(pointTwo.second + 0.05)
+                    ) {
+                        pointTwo = pointTwo.first + (end.focus.latitude - start.focus.latitude).toDegrees() to
+                                pointTwo.second + (end.focus.longitude - start.focus.longitude).toDegrees()
+                        false
+                    } else true
+                }
             )
         ) {
-            val pointOne = 55.568548 to 37.568604
-            val pointTwo = 55.929444 to 37.518434
-            val pointThree = 60.929444 to 37.518434
 
             image(pointOne, Icons.Filled.Home)
 
@@ -75,7 +85,7 @@ fun App() {
                 )
             }
 
-            line(pointOne, pointTwo)
+            line(pointOne, pointTwo, id = "Line")
             text(pointOne, "Home")
 
             centerCoordinates?.let {

maps-kt-compose/src/commonMain/kotlin/centre/sciprog/maps/compose/MapView.kt

@@ -17,6 +17,7 @@ data class MapViewConfig(
     val onClick: MapViewPoint.() -> Unit = {},
     val onViewChange: MapViewPoint.() -> Unit = {},
     val onSelect: (GmcBox) -> Unit = {},
+    val onDrag: (MapViewPoint, MapViewPoint) -> Boolean = { _, _ -> true },
     val zoomOnSelect: Boolean = true
 )
 
@@ -49,15 +50,16 @@ fun MapView(
     )
 }
 
-internal fun GmcBox.getComputeViewPoint(mapTileProvider: MapTileProvider): (canvasSize: DpSize) -> MapViewPoint = { canvasSize ->
-    val zoom = log2(
-        min(
-            canvasSize.width.value / width,
-            canvasSize.height.value / height
-        ) * PI / mapTileProvider.tileSize
-    )
-    MapViewPoint(center, zoom)
-}
+internal fun GmcBox.getComputeViewPoint(mapTileProvider: MapTileProvider): (canvasSize: DpSize) -> MapViewPoint =
+    { canvasSize ->
+        val zoom = log2(
+            min(
+                canvasSize.width.value / width,
+                canvasSize.height.value / height
+            ) * PI / mapTileProvider.tileSize
+        )
+        MapViewPoint(center, zoom)
+    }
 
 @Composable
 fun MapView(

maps-kt-compose/src/jvmMain/kotlin/centre/sciprog/maps/compose/MapViewJvm.kt

@@ -131,7 +131,7 @@ actual fun MapView(
                                     rect.bottomRight.toDpOffset().toGeodetic()
                                 )
                                 config.onSelect(gmcBox)
-                                if(config.zoomOnSelect) {
+                                if (config.zoomOnSelect) {
                                     val newViewPoint = gmcBox.getComputeViewPoint(mapTileProvider).invoke(canvasSize)
 
                                     config.onViewChange(newViewPoint)
@@ -144,6 +144,14 @@ actual fun MapView(
                             val dpPos = DpOffset(dragStart.x.toDp(), dragStart.y.toDp())
                             config.onClick(MapViewPoint(dpPos.toGeodetic(), viewPoint.zoom))
                             drag(change.id) { dragChange ->
+                                val dpStartPos =
+                                    DpOffset(dragChange.previousPosition.x.toDp(), dragChange.previousPosition.y.toDp())
+                                val dpEndPos = DpOffset(dragChange.position.x.toDp(), dragChange.position.y.toDp())
+                                if (!config.onDrag(
+                                        MapViewPoint(dpStartPos.toGeodetic(), viewPoint.zoom),
+                                        MapViewPoint(dpEndPos.toGeodetic(), viewPoint.zoom)
+                                    )
+                                ) return@drag
                                 val dragAmount = dragChange.position - dragChange.previousPosition
                                 val newViewPoint = viewPoint.move(
                                     -dragAmount.x.toDp().value / tileScale,

maps-kt-core/src/commonMain/kotlin/centre/sciprog/maps/Utils.kt

@@ -0,0 +1,7 @@
+package centre.sciprog.maps
+
+import kotlin.math.PI
+
+fun Double.toDegrees() = this * 180 / PI
+
+fun Double.toRadians() = this * PI / 180