persistable sclass GSI extends AbstractHasHi15Color is G2Drawable, IPixelSet {

  int y1; // starting y coordinate

  int[] rowStarts; // where in xData each row starts

  int[] xData; // all x coordinates in a long list (x1, x2, x1, x2, ...)

  *(int *y1, int[] *rowStarts, int[] *xData) {}

  public int getHeight() { ret rowStarts.length; }

  int y2() { ret y1+rowStarts.length; }

  // bounds are calculated & cached transiently

  public simplyCached Rect bounds() {

    int x1 = Int.MAX_VALUE, x2 = 0;

    for (int i = 0; i < xData.length; i += 2) {

      x1 = min(x1, xData[i]);

      x2 = max(x2, xData[i+1]);

    }

    ret rectFromPoints(x1, y1, x2, y2());

  }

  public bool contains(Pt p) { ret contains(p.x, p.y); }

  public bool contains(int x, int y) {

    if (y < y1 || y >= y2()) false;

    int i1 = rowStart(y), i2 = rowEnd(y);

    for (int i = i1; i < i2; i += 2)

      if (x < xData[i+1])

        // found the right entry to check

        ret x >= xData[i];

    false;

  }

  int rowStart(int y) { ret rowStarts[y-y1]; }

  int rowEnd(int y) {

    ret y == y2()-1 ? rowStarts.length : rowStarts[y-y1+1];

  }

  public void drawOn(Graphics2D g) {

    g.setColor(color());

    int h = height();

    for y to h: {

      int i1 = rowStart(y-y1), i2 = rowEnd(y-y1);

      for (int i = i1; i < i2; i += 2) {

        int x1 = xData[i], x2 = xData[i+1];

        if (x1 < x2)

          g.drawLine(x1, y1+y, x2-1, y1+y);

      }

    }

  }

}