Move the curve drawing curve by control points to Context2d.

canvas/src/commonMain/kotlin/org/jetbrains/letsPlot/core/canvas/Context2d.kt

@@ -60,6 +60,41 @@ interface Context2d {
  fun setTransform(m11: Double, m12: Double, m21: Double, m22: Double, dx: Double, dy: Double)
  fun setLineDash(lineDash: DoubleArray)
  fun measureText(str: String): Double
+
+ // https://github.com/d3/d3/blob/9364923ee2b35ec2eb80ffc4bdac12a7930097fc/src/svg/line.js#L236
+ fun bSplineInterpolation(points: List<Vec<*>>) {
+ fun lineDot4(a: List<Double>, b: List<Double>): Double {
+ // returns the dot product of the given four-element vectors
+ return a[0] * b[0] + a[1] * b[1] + a[2] * b[2] + a[3] * b[3]
+ }
+ // Matrix to transform basis (b-spline) control points to bezier control points.
+ val lineBasisBezier1 = listOf(0.0, 2.0 / 3.0, 1.0 / 3.0, 0.0)
+ val lineBasisBezier2 = listOf(0.0, 1.0 / 3.0, 2.0 / 3.0, 0.0)
+ val lineBasisBezier3 = listOf(0.0, 1.0 / 6.0, 2.0 / 3.0, 1.0 / 6.0)
+
+ val px = arrayListOf(points[0].x, points[0].x, points[0].x, points[1].x)
+ val py = arrayListOf(points[0].y, points[0].y, points[0].y, points[1].y)
+
+ moveTo(points[0].x, points[0].y)
+ lineTo(
+ lineDot4(lineBasisBezier3, px),
+ lineDot4(lineBasisBezier3, py)
+ )
+ for (i in 2..points.size) {
+ val curPoint = if (i < points.size) points[i] else points.last()
+ px.removeFirst(); px.add(curPoint.x)
+ py.removeFirst(); py.add(curPoint.y)
+ bezierCurveTo(
+ lineDot4(lineBasisBezier1, px),
+ lineDot4(lineBasisBezier1, py),
+ lineDot4(lineBasisBezier2, px),
+ lineDot4(lineBasisBezier2, py),
+ lineDot4(lineBasisBezier3, px),
+ lineDot4(lineBasisBezier3, py)
+ )
+ }
+ lineTo(points.last().x, points.last().y)
+ }
 }
 
 fun Context2d.drawImage(snapshot: Snapshot, p: Vec<*>) = drawImage(snapshot, p.x, p.y)

livemap/src/commonMain/kotlin/org/jetbrains/letsPlot/livemap/chart/path/PathRenderer.kt

@@ -230,36 +230,11 @@ open class PathRenderer : Renderer {
 
 class CurveRenderer : PathRenderer() {
  override fun drawPath(points: List<WorldPoint>, ctx: Context2d) {
- fun lineDot4(a: List<Double>, b: List<Double>): Double {
- // returns the dot product of the given four-element vectors
- return a[0] * b[0] + a[1] * b[1] + a[2] * b[2] + a[3] * b[3]
+ if (points.size < 3) {
+ // linear
+ super.drawPath(points, ctx)
+ } else {
+ ctx.bSplineInterpolation(points)
  }
- // Matrix to transform basis (b-spline) control points to bezier control points.
- val lineBasisBezier1 = listOf(0.0, 2.0 / 3.0, 1.0 / 3.0, 0.0)
- val lineBasisBezier2 = listOf(0.0, 1.0 / 3.0, 2.0 / 3.0, 0.0)
- val lineBasisBezier3 = listOf(0.0, 1.0 / 6.0, 2.0 / 3.0, 1.0 / 6.0)
-
- val px = arrayListOf(points[0].x, points[0].x, points[0].x, points[1].x)
- val py = arrayListOf(points[0].y, points[0].y, points[0].y, points[1].y)
-
- ctx.moveTo(points[0].x, points[0].y)
- ctx.lineTo(
- lineDot4(lineBasisBezier3, px),
- lineDot4(lineBasisBezier3, py)
- )
- for (i in 2..points.size) {
- val curPoint = if (i < points.size) points[i] else points.last()
- px.removeFirst(); px.add(curPoint.x)
- py.removeFirst(); py.add(curPoint.y)
- ctx.bezierCurveTo(
- lineDot4(lineBasisBezier1, px),
- lineDot4(lineBasisBezier1, py),
- lineDot4(lineBasisBezier2, px),
- lineDot4(lineBasisBezier2, py),
- lineDot4(lineBasisBezier3, px),
- lineDot4(lineBasisBezier3, py)
- )
- }
- ctx.lineTo(points.last().x, points.last().y)
  }
 }