[orx-fcurve] Fix bug in Segment2D.tForX

orx-fcurve/src/commonMain/kotlin/FCurve.kt

@@ -11,6 +11,9 @@ import kotlin.math.abs
  * Find the (first) t value for a given [x] value
  */
 private fun Segment2D.tForX(x: Double): Double {
+    if (x == start.x) return 0.0
+    if (x == end.x) return 1.0
+
     if (linear) {
         return (x - start.x) / (end.x - start.x)
     } else {
@@ -155,7 +158,7 @@ data class FCurve(val segments: List<Segment2D>) {
         if (segments.isEmpty()) {
             return Pair(0.0, null)
         }
-        if (t < segments.first().start.x) {
+        if (t <= segments.first().start.x) {
             val segment = segments.first()
             return Pair(segment.start.y, segment)
         } else if (t > segments.last().end.x) {

orx-fcurve/src/commonTest/kotlin/TestEFCurve.kt

@@ -1,4 +1,5 @@
 import org.openrndr.extra.fcurve.efcurve
+import org.openrndr.extra.fcurve.fcurve
 import kotlin.test.Test
 import kotlin.test.assertEquals
 
@@ -30,4 +31,11 @@ class TestEFCurve {
         assertEquals("M0 L1.0, ${0.0} L1.0, ${1.0}", efcurve("M0 (L1.0, {it})[2]"))
         assertEquals("M0 L1.0, ${0.0} L1.0, ${1.0} L1.0, ${0.0} L1.0, ${1.0} L1.0, ${0.0} L1.0, ${1.0}", efcurve("M0 ((L1.0, {it})[2])[3]"))
     }
+
+    @Test
+    fun testContinuity() {
+        val fc = fcurve("Q1 25% 3 100 Q1 25% 3 0 Q1 25% 3 100 Q1 25% 3 0")
+        val s = fc.sampler()
+        assertEquals(0.0,  s(6.0))
+    }
 }