JFreeChart different colors in different regions for the same dataSeries

Question

In JFreeChart I'm trying to color different regions of an XY line chart/curve based on y value. I'm overriding the XYLineAndShapeRenderer's getItemPaint(int row, int col), however I'm not sure how it handles the coloring of the line between the xs since it's only getting itemPaint on the x (integer values).

final XYLineAndShapeRenderer renderer = new XYLineAndShapeRenderer() {
    @Override

    @Override
    public Paint getItemPaint(int row, int col) {
        System.out.println(col+","+dataset.getY(row, col));
        double y=dataset.getYValue(row, col);
        if(y<=3)return ColorUtil.hex2Rgb("#7DD2F7");
        if(y<=4)return ColorUtil.hex2Rgb("#9BCB3B");
        if(y<=5)return ColorUtil.hex2Rgb("#FFF100");
        if(y<=6)return ColorUtil.hex2Rgb("#FAA419");
        if(y<=10)return ColorUtil.hex2Rgb("#ED1B24");

        //getPlot().getDataset(col).
        return super.getItemPaint(row,col);
    }
}

GrahamA · Accepted Answer · 2012-08-15T11:33:05.623

It looks like the handling of the colouring between lines is implemented in drawFirstPassShape

The line colour appears to be based on the preceding point

enter image description here

This modification to your XYLineAndShapeRenderer uses a gradient fill to blend the line colour.

XYLineAndShapeRenderer renderer = new XYLineAndShapeRenderer(){
        @Override
        public Paint getItemPaint(int row, int col) {
            Paint cpaint = getItemColor(row, col);
            if (cpaint == null) {
                cpaint = super.getItemPaint(row, col);
            }
            return cpaint;
        }

    public Color getItemColor(int row, int col) {
        System.out.println(col + "," + dataset.getY(row, col));
        double y = dataset.getYValue(row, col);
        if(y<=3) return Color.black;
        if(y<=4) return Color.green;;
        if(y<=5) return Color.red;;
        if(y<=6) return Color.yellow;;
        if(y<=10) return Color.orange;;
        return null;
    }

    @Override
    protected void drawFirstPassShape(Graphics2D g2, int pass, int series,
        int item, Shape shape) {
        g2.setStroke(getItemStroke(series, item));
        Color c1 = getItemColor(series, item);
        Color c2 = getItemColor(series, item - 1);
        GradientPaint linePaint = new GradientPaint(0, 0, c1, 0, 300, c2);
        g2.setPaint(linePaint);
        g2.draw(shape);
    }
};

enter image description here

I've removed ColorUtil.hex2Rgb as I don't have access to that class/method. You may want to modify GradientPaint to take account of the distance/gradient between points.

JFreeChart different colors in different regions for the same dataSeries

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