Canvas.drawLines displaying disjointed segments [duplicate]

Answer 1

I just ran into this issue tonight. For anyone else facing this, the problem is that Android doesn't draw from point 1 to point 2, then point 2 to point 3, point 3 to point 4, etc. It will draw point 1 to 2, then point 3 to 4, etc. So you can also push the previous point twice into whatever data structure you use (I used Vector). So:

private Vector<Float> mPoints = new Vector<Float>();
private float mLastX = Float.NaN;
private float mLastY = Float.NaN;

public void addPoint(float x, float y) {
    if (mLastX == Float.NaN || mLastY == Float.NaN) {
        mLastX = x;
        mLastY = y;
    } else {
        mPoints.add(mLastX);
        mPoints.add(mLastY);
        mPoints.add(x);
        mPoints.add(y);

        mLastX = x;
        mLastY = y;
    }
}

Then just make sure to convert your mPoints to a float[] and pass that to canvas.drawLines().

Answer 2

What you get is exactly what is specified in the drawLines documentation.

One way of doing what you want would be to construct a Path from that data, and use drawPath rather than drawLines. Something like:

Path _path = new Path();
_path.moveTo(_data[0], _data[1]);
for (int i=2; i<_data.length; i+=2) {
  _path.lineTo(_data[i], _data[i+1]);
}

Then draw it with:

_canvas.drawPath(_path, _paint)

From the Path docs:

The Path class encapsulates compound (multiple contour) geometric paths consisting of straight line segments, quadratic curves, and cubic curves. It can be drawn with canvas.drawPath(path, paint), either filled or stroked (based on the paint's Style)

So you might have to change you're paint's style to get the right effect.