Add support and demo for the stroke-dashoffset attribute

Author: IKupriyanov-HORIS

demo/plot/compose-desktop/src/main/kotlin/demo/plot/various/StrokeDashCompose.kt

@@ -0,0 +1,37 @@
+/*
+ * Copyright (c) 2024 JetBrains s.r.o.
+ * Use of this source code is governed by the MIT license that can be found in the LICENSE file.
+ */
+
+package demo.plot.various
+
+import androidx.compose.foundation.layout.*
+import androidx.compose.material.MaterialTheme
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.unit.dp
+import androidx.compose.ui.window.Window
+import androidx.compose.ui.window.application
+import org.jetbrains.letsPlot.skia.compose.PlotPanel
+import plotSpec.StrokeDashSpec
+
+@OptIn(ExperimentalLayoutApi::class)
+fun main() = application {
+    Window(onCloseRequest = ::exitApplication, title = "StrokeDash (Compose Desktop)") {
+        MaterialTheme {
+            FlowRow(
+                modifier = Modifier.fillMaxSize().padding(start = 10.dp, top = 10.dp, end = 10.dp, bottom = 10.dp),
+            ) {
+                StrokeDashSpec().createFigureList().forEach { figure ->
+                    Column {
+                        PlotPanel(
+                            figure = figure,
+                            modifier = Modifier.size(610.dp)
+                        ) { computationMessages ->
+                            computationMessages.forEach { println("[DEMO APP MESSAGE] $it") }
+                        }
+                    }
+                }
+            }
+        }
+    }
+}

demo/plot/shared/src/main/kotlin/plotSpec/StrokeDashSpec.kt

@@ -0,0 +1,21 @@
+/*
+ * Copyright (c) 2024 JetBrains s.r.o.
+ * Use of this source code is governed by the MIT license that can be found in the LICENSE file.
+ */
+
+package plotSpec
+
+import org.jetbrains.letsPlot.Figure
+import org.jetbrains.letsPlot.geom.geomSegment
+import org.jetbrains.letsPlot.ggplot
+
+class StrokeDashSpec : PlotDemoSpec {
+    override fun createFigureList(): List<Figure> {
+        return listOf(
+            ggplot()
+                    + geomSegment(x=0, y=20, xend = 100, yend=20, linetype = listOf(5, listOf(10, 5)))
+                    + geomSegment(x=0, y=10, xend = 100, yend=10, linetype = listOf(0, listOf(10, 5)))
+                    + geomSegment(x=0, y=0, xend = 100, yend=0),
+        )
+    }
+}

platf-skia/src/commonMain/kotlin/org/jetbrains/letsPlot/skia/mapping/svg/attr/SvgShapeMapping.kt

@@ -18,6 +18,7 @@ internal abstract class SvgShapeMapping<TargetT : Figure> : SvgAttrMapping<Targe
             SvgShape.STROKE.name -> target.stroke = toColor(value)
             SvgShape.STROKE_OPACITY.name -> target.strokeOpacity = value!!.asFloat
             SvgShape.STROKE_WIDTH.name -> target.strokeWidth = value!!.asFloat
+            SvgShape.STROKE_DASHOFFSET.name -> target.strokeDashOffset = value?.asFloat ?: 0f
             SvgConstants.SVG_STROKE_DASHARRAY_ATTRIBUTE -> {
                 val strokeDashArray = (value as String).split(",").map(String::toFloat)
                 target.strokeDashArray = strokeDashArray

platf-skia/src/commonMain/kotlin/org/jetbrains/letsPlot/skia/shape/Figure.kt

@@ -13,6 +13,7 @@ internal abstract class Figure : Element() {
     var strokeWidth: Float by visualProp(1f)
     var strokeOpacity: Float by visualProp(1f)
     var strokeDashArray: List<Float>? by visualProp(null)
+    var strokeDashOffset: Float by visualProp(0f)
     var strokeMiter: Float? by visualProp(null) // not mandatory, default works fine
 
     var fill: Color4f? by visualProp(null)
@@ -30,6 +31,13 @@ internal abstract class Figure : Element() {
         Figure::strokeMiter,
         managed = true
     ) {
-        return@computedProp strokePaint(stroke, strokeWidth, strokeOpacity, strokeDashArray, strokeMiter)
+        return@computedProp strokePaint(
+            stroke = stroke,
+            strokeWidth = strokeWidth,
+            strokeOpacity = strokeOpacity,
+            strokeDashArray = strokeDashArray,
+            strokeDashOffset = strokeDashOffset,
+            strokeMiter = strokeMiter
+        )
     }
 }

platf-skia/src/commonMain/kotlin/org/jetbrains/letsPlot/skia/shape/Util.kt

@@ -157,7 +157,8 @@ fun strokePaint(
     strokeWidth: Float = 1f,
     strokeOpacity: Float = 1f,
     strokeDashArray: List<Float>? = null,
-    strokeMiter: Float? = null // not mandatory, default works fine
+    strokeDashOffset: Float = 0f, // not mandatory, default works fine
+    strokeMiter: Float? = null
 ) : Paint? {
     if (stroke == null) return null
     if (strokeOpacity == 0f) return null
@@ -173,7 +174,7 @@ fun strokePaint(
     paint.color4f = stroke.withA(strokeOpacity)
     paint.strokeWidth = strokeWidth
     strokeMiter?.let { paint.strokeMiter = it }
-    strokeDashArray?.let { paint.pathEffect = makeDash(it.toFloatArray(), 0.0f) }
+    strokeDashArray?.let { paint.pathEffect = makeDash(it.toFloatArray(), strokeDashOffset) }
     return paint
 }