How To Create a Line Chart

Here is a short example on how to create and display a line chart.

images/howto_linechart.png

// obtain data series
double[] seriesA_y = randomData(20);
double[] seriesA_x = IntStream.range(0, 20).mapToDouble(i->i/19.0).toArray();
double[] seriesB_y = randomData(30);
double[] seriesB_x = randomData(30);
Arrays.sort(seriesB_x);
// create Lines objects, one solid the other dashed
Lines lineA = new Lines();
Lines lineB = new Lines();
lineB.setStrokePattern(0xf0f0);
// add line segments to A
for(int i=0; i<seriesA_y.length-1; i++){
   double x1=seriesA_x[i], x2=seriesA_x[i+1];
   double y1=seriesA_y[i], y2=seriesA_y[i+1];
   SegmentDetails segment = lineA.addSegment(x1, y1, x2, y2);
   segment.setColor(Color.RED);
}
// add line segments to B (the short way)
ArrayList<SegmentDetails> segmentsB = lineB.addLineStrip(seriesB_x, seriesB_y);
segmentsB.forEach(seg->seg.setColor(Color.BLUE));
// use a coordinate system for display
CoordSysRenderer coordsys = new CoordSysRenderer();
coordsys.setCoordinateView(-1,-1,1,1);
// set the content renderer of the coordinate system 
// we want to render Lines objects
LinesRenderer lineContent = new LinesRenderer();
lineContent.addItemToRender(lineA).addItemToRender(lineB);
coordsys.setContent(lineContent);

// display within a JFrame
JFrame frame = new JFrame();
boolean useOpenGL = true;
JPlotterCanvas canvas = useOpenGL ? new BlankCanvas() : new BlankCanvasFallback();
canvas.setRenderer(coordsys);
canvas.asComponent().setPreferredSize(new Dimension(700, 400));
canvas.asComponent().setBackground(Color.WHITE);
frame.getContentPane().add(canvas.asComponent());
frame.setTitle("linechart");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
canvas.addCleanupOnWindowClosingListener(frame);
// make visible on AWT event dispatch thread
SwingUtilities.invokeLater(()->{
   frame.pack();
   frame.setVisible(true);
});

If desired, we can also show the area under/over the curve. To do this we add the following lines.

images/howto_linechart_area.png

// (optional) area under curve with transparency
Triangles areaA = new Triangles();
areaA.setGlobalAlphaMultiplier(0.2);
// add area quads under each segment
for(SegmentDetails segment: lineA.getSegments()){
   Point2D pL=segment.p0, pR=segment.p1;
   if(Math.signum(pL.getY()) == Math.signum(pR.getY())){
      // points are on same side of x-axis
      ArrayList<TriangleDetails> quad = areaA.addQuad(
            pL.getX(), 0, pL.getX(), pL.getY(), 
            pR.getX(), pR.getY(), pR.getX(), 0);
      quad.forEach(tri->tri.setColor(Color.RED));
   } else {
      // segment intersects x-axis, need to find intersection
      double x0=pL.getX(),y0=pL.getY(), x2=pR.getX(), y2=pR.getY();
      double m = (y2-y0)/(x2-x0);
      // solving for x1 in (x1-x0)*m+y0 = 0 --> 1x = x0-y0/m;
      double x1 = x0-y0/m;
      areaA.addTriangle(x0, y0, x1, 0, x0, 0).setColor(Color.RED);
      areaA.addTriangle(x2, y2, x1, 0, x2, 0).setColor(Color.RED);
   }
}
// use a TriangleRenderer for the Triangles
TrianglesRenderer areaContent = new TrianglesRenderer();
areaContent.addItemToRender(areaA);
// append the line renderer to the triangle renderer and use as new content
coordsys.setContent(areaContent.withAppended(lineContent));
canvas.scheduleRepaint();