Make pin pointer rotated

app/src/main/java/ru/spbu/depnav/ui/component/PinPointer.kt

@@ -47,9 +47,12 @@ import ovh.plrapps.mapcompose.utils.AngleDegree
 import ovh.plrapps.mapcompose.utils.Point
 import ru.spbu.depnav.data.model.Marker
 import ru.spbu.depnav.utils.map.LineSegment
+import ru.spbu.depnav.utils.map.bottom
+import ru.spbu.depnav.utils.map.centroid
 import ru.spbu.depnav.utils.map.contains
 import ru.spbu.depnav.utils.map.left
 import ru.spbu.depnav.utils.map.rectangularVisibleArea
+import ru.spbu.depnav.utils.map.right
 import ru.spbu.depnav.utils.map.rotation
 import ru.spbu.depnav.utils.map.top
 
@@ -153,51 +156,22 @@ private data class PinPointerPose(
     }
 }
 
-private const val EPSILON = 1e-5
-
 private fun calculatePointerPose(visibleArea: VisibleArea, pin: Point): PinPointerPose {
-    val topBorder = visibleArea.top()
-    val leftBorder = visibleArea.left()
-
-    val horizontalFraction = topBorder.fractionOfClosestPointTo(pin)
-    val verticalFraction = leftBorder.fractionOfClosestPointTo(pin)
+    val centroidPinSegment = LineSegment(visibleArea.centroid(), pin)
+    val direction = centroidPinSegment.slope() - 90
 
-    return when {
-        // Corners
-        horizontalFraction < EPSILON && verticalFraction < EPSILON -> {
-            val direction = LineSegment(topBorder.p1, pin).slope() - 90
-            PinPointerPose(PinPointerPose.Side.TOP, 0.0, direction)
-        }
-        horizontalFraction > 1.0 - EPSILON && verticalFraction < EPSILON -> {
-            val direction = LineSegment(topBorder.p2, pin).slope() - 90
-            PinPointerPose(PinPointerPose.Side.TOP, 1.0, direction)
-        }
-        horizontalFraction < EPSILON && verticalFraction > 1.0 - EPSILON -> {
-            val direction = LineSegment(leftBorder.p2, pin).slope() - 90
-            PinPointerPose(PinPointerPose.Side.BOTTOM, 0.0, direction)
-        }
-        horizontalFraction > 1.0 - EPSILON && verticalFraction > 1.0 - EPSILON -> {
-            val direction = LineSegment(with(visibleArea) { Point(p3x, p3y) }, pin).slope() - 90
-            PinPointerPose(PinPointerPose.Side.BOTTOM, 1.0, direction)
-        }
-        // Sides
-        horizontalFraction < EPSILON -> {
-            val direction = (topBorder.slope() - 180) - 90
-            PinPointerPose(PinPointerPose.Side.LEFT, verticalFraction, direction)
-        }
-        horizontalFraction > 1.0 - EPSILON -> {
-            val direction = topBorder.slope() - 90
-            PinPointerPose(PinPointerPose.Side.RIGHT, verticalFraction, direction)
-        }
-        verticalFraction < EPSILON -> {
-            val direction = (leftBorder.slope() - 180) - 90
-            PinPointerPose(PinPointerPose.Side.TOP, horizontalFraction, direction)
-        }
-        verticalFraction > 1.0 - EPSILON -> {
-            val direction = leftBorder.slope() - 90
-            PinPointerPose(PinPointerPose.Side.BOTTOM, horizontalFraction, direction)
-        }
-        // Pin is inside the area
-        else -> throw IllegalArgumentException("Pin lies inside the visible area")
+    visibleArea.top().fractionOfIntersectionWith(centroidPinSegment)?.let { fraction ->
+        return PinPointerPose(PinPointerPose.Side.TOP, fraction, direction)
+    }
+    visibleArea.right().fractionOfIntersectionWith(centroidPinSegment)?.let { fraction ->
+        return PinPointerPose(PinPointerPose.Side.RIGHT, fraction, direction)
     }
+    visibleArea.bottom().fractionOfIntersectionWith(centroidPinSegment)?.let { fraction ->
+        return PinPointerPose(PinPointerPose.Side.BOTTOM, fraction, direction)
+    }
+    visibleArea.left().fractionOfIntersectionWith(centroidPinSegment)?.let { fraction ->
+        return PinPointerPose(PinPointerPose.Side.LEFT, fraction, direction)
+    }
+
+    throw IllegalArgumentException("Pin lies inside the visible area")
 }

app/src/main/java/ru/spbu/depnav/utils/map/LineSegment.kt

@@ -40,10 +40,27 @@ data class LineSegment(val p1: Point, val p2: Point) {
     fun containsProjectionOf(p: Point) = fractionOfProjectionOf(p) in 0.0..1.0
 
     /**
-     * Returns the fraction from the start of this segment to its point that is the closest to the
-     * specified point.
+     * Returns the fraction from the start of this segment to its intersection point with the other
+     * segment if such point exists, or null otherwise.
      */
-    fun fractionOfClosestPointTo(p: Point) = fractionOfProjectionOf(p).coerceIn(0.0, 1.0)
+    fun fractionOfIntersectionWith(l: LineSegment): Double? {
+        // See https://en.wikipedia.org/wiki/Line%E2%80%93line_intersection#Given_two_points_on_each_line_segment
+        val denominator = (p1.x - p2.x) * (l.p1.y - l.p2.y) - (p1.y - p2.y) * (l.p1.x - l.p2.x)
+
+        val numerator1 = (p1.x - l.p1.x) * (l.p1.y - l.p2.y) - (p1.y - l.p1.y) * (l.p1.x - l.p2.x)
+        val t1 = numerator1 / denominator
+        if (t1 < 0 || t1 > 1) {
+            return null
+        }
+
+        val numerator2 = (p1.x - p2.x) * (p1.y - l.p1.y) - (p1.y - p2.y) * (p1.x - l.p1.x)
+        val t2 = -(numerator2 / denominator)
+        if (t2 < 0 || t2 > 1) {
+            return null
+        }
+
+        return t1
+    }
 
     private fun fractionOfProjectionOf(p: Point): Double {
         val vecP1ToP2 = Point(p2.x - p1.x, p2.y - p1.y)

app/src/main/java/ru/spbu/depnav/utils/map/VisibleArea.kt

@@ -94,16 +94,31 @@ fun MapState.rectangularVisibleArea(
     return VisibleArea(p1x, p1y, p2x, p2y, p3x, p3y, p4x, p4y)
 }
 
+/**
+ * Centroid of the area.
+ */
+fun VisibleArea.centroid() = Point((p1x + p3x) / 2, (p1y + p3y) / 2)
+
 /**
  * Top border of the area.
  */
 fun VisibleArea.top() = LineSegment(Point(p1x, p1y), Point(p2x, p2y))
 
+/**
+ * Bottom border of the area.
+ */
+fun VisibleArea.bottom() = LineSegment(Point(p4x, p4y), Point(p3x, p3y))
+
 /**
  * Left border of the area.
  */
 fun VisibleArea.left() = LineSegment(Point(p1x, p1y), Point(p4x, p4y))
 
+/**
+ * Right border of the area.
+ */
+fun VisibleArea.right() = LineSegment(Point(p2x, p2y), Point(p3x, p3y))
+
 /**
  * Returns true if the provided point lies inside this area, or false otherwise.
  *