How to make line with rounded (smooth) corners with AndroidPlot

android, androidplot

Solution

You can use Path.cubicTo() method. It draws a line using cubic spline algorithm which results in the smoothing effect you want.

Checkout the answer to a similar question here, where a guy is talking about cubic splines. There is a short algorithm showing how to calculate input parameters for `Path.cubicTo()` method. You can play with divider values to achieve required smoothness. For example, in the picture below I divided by 5 instead of 3. Hope this helps.

I have spent some time and implemented a `SplineLineAndPointFormatter` class, which does the stuff you need in androidplot library. It uses same technics. Here is how androidplot example applications looks like. You just need to use it instead of `LineAndPointFormatter`.

Here is code example and the class I wrote.

f1 = new SplineLineAndPointFormatter(color.getColor(), null, 
      Color.argb(60, color.getRed(), color.getGreen(), color.getBlue()), null);
plot.addSeries(series1, f1);

Here is the class doing the magic. It is based on version 0.6.1 of androidplot library.

package com.androidplot.xy;

import android.graphics.Canvas;
import android.graphics.Path;
import android.graphics.PointF;
import android.graphics.RectF;

import com.androidplot.ui.SeriesRenderer;
import com.androidplot.util.ValPixConverter;

public class SplineLineAndPointFormatter extends LineAndPointFormatter {

    public SplineLineAndPointFormatter() { }

    public SplineLineAndPointFormatter(Integer lineColor, Integer vertexColor, Integer fillColor) {
        super(lineColor, vertexColor, fillColor, null);
    }

    public SplineLineAndPointFormatter(Integer lineColor, Integer vertexColor, Integer fillColor, FillDirection fillDir) {
        super(lineColor, vertexColor, fillColor, null, fillDir);
    }

    @Override
    public Class<? extends SeriesRenderer> getRendererClass() {
        return SplineLineAndPointRenderer.class;
    }

    @Override
    public SeriesRenderer getRendererInstance(XYPlot plot) {
        return new SplineLineAndPointRenderer(plot);
    }

    public static class SplineLineAndPointRenderer extends LineAndPointRenderer<BezierLineAndPointFormatter> {

        static class Point {
            public float x, y, dx, dy;
            public Point(PointF pf) { x = pf.x; y = pf.y; }
        }

        private Point prev, point, next;
        private int pointsCounter;

        public SplineLineAndPointRenderer(XYPlot plot) {
            super(plot);
        }

        @Override
        protected void appendToPath(Path path, final PointF thisPoint, PointF lastPoint) {
            pointsCounter--;

            if (point == null) {
                point = new Point(thisPoint);
                point.dx = ((point.x - prev.x) / 5);
                point.dy = ((point.y - prev.y) / 5);
                return;

            } else if (next == null) {
                next = new Point(thisPoint);
            } else {
                prev = point;
                point = next;
                next = new Point(thisPoint);
            }

            point.dx = ((next.x - prev.x) / 5);
            point.dy = ((next.y - prev.y) / 5);
            path.cubicTo(prev.x + prev.dx, prev.y + prev.dy, point.x - point.dx, point.y - point.dy, point.x, point.y);

            if (pointsCounter == 1) { // last point
                next.dx = ((next.x - point.x) / 5);
                next.dy = ((next.y - point.y) / 5);
                path.cubicTo(point.x + point.dx, point.y + point.dy, next.x - next.dx, next.y - next.dy, next.x, next.y);
            }

        }

        @Override
        protected void drawSeries(Canvas canvas, RectF plotArea, XYSeries series, LineAndPointFormatter formatter) {

            Number y = series.getY(0);
            Number x = series.getX(0);
            if (x == null || y == null) throw new IllegalArgumentException("no null values in xyseries permitted");

            XYPlot p = getPlot();
            PointF thisPoint = ValPixConverter.valToPix(x, y, plotArea,
                    p.getCalculatedMinX(), p.getCalculatedMaxX(), p.getCalculatedMinY(), p.getCalculatedMaxY());

            prev = new Point(thisPoint);
            point = next = null;
            pointsCounter = series.size();

            super.drawSeries(canvas, plotArea, series, formatter);
        }
    }
}

Problem

Original source

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