ADDITIONAL SYSTEM INFORMATION :
Java 11.0.7
JavaFX 14.0.1

A DESCRIPTION OF THE PROBLEM :
When drawing a LineChart with a line (-fx-stroke-width) > 1px and non-negative Y axis there are no artifacts present. When the Y axis is changed to include negative values, clearly visible artifacts are created on the chart lines.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Create or set Y axis lower bound to a negative value.
Draw a line on a LineChart with a -fx-stroke-width of 20px (for example).


EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Rectangular form from origin to dest with a width as specified.
ACTUAL -
Expected result but with additional artifacts at point of origin.

---------- BEGIN SOURCE ----------
package demo.fxbug;

import javafx.application.Application;
import javafx.collections.ObservableList;
import javafx.scene.Scene;
import javafx.scene.chart.LineChart;
import javafx.scene.chart.NumberAxis;
import javafx.scene.chart.XYChart;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

/**
 * JavaFX App
 */
public class App extends Application {
    
    @Override
    public void start(Stage stage) {
        var xAxis = new NumberAxis();
        var yAxis = new NumberAxis(-10.0, 10, 1.0);
        var chart = new LineChart<Number, Number>(xAxis, yAxis);
        ObservableList<XYChart.Series<Number, Number>> barChartData = chart.getData();
        XYChart.Series<Number, Number> barSeries1 = new XYChart.Series<>();
        XYChart.Data<Number, Number> point1 = new XYChart.Data<>(100L, 0);
        XYChart.Data<Number, Number> point2 = new XYChart.Data<>(100L, 10);
        barSeries1.getData().addAll(point1, point2);
        barChartData.add(barSeries1);
        chart.setCreateSymbols(false);
        barSeries1.getNode().setStyle("-fx-stroke: rgba(0,0,0,1.0); -fx-stroke-width: 20px; -fx-stroke-line-cap: butt; ");

        var scene = new Scene(new StackPane(chart), 640, 480);
        stage.setScene(scene);
        stage.show();
    }

    public static void main(String[] args) {
        launch();
    }
    
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
None.

FREQUENCY : always