android - 如果有点，如何设置区域并找到特定区域？

Question

我有所有的点来画一条线并在画布上正确显示这些点。但是现在我想在用户触摸时在该现有线上画另一条线。我的问题是，如何找到用户触摸该线的内部或线外？

Answer 1

I have a suggestion.

This is a thought based on Google Maps and Polylines but could should easily be adapted to a Canvas 2DLine situation too, I think.

Use this method to calculate the distance between two LatLng points:

/** distance in meters **/
private float distFrom(double lat1, double lng1, double lat2, double lng2) {
    double earthRadius = 3958.75;
    double dLat = Math.toRadians(lat2 - lat1);
    double dLng = Math.toRadians(lng2 - lng1);
    double a = Math.sin(dLat / 2) * Math.sin(dLat / 2)
            + Math.cos(Math.toRadians(lat1))
            * Math.cos(Math.toRadians(lat2)) * Math.sin(dLng / 2)
            * Math.sin(dLng / 2);
    double c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
    double dist = earthRadius * c;

    int meterConversion = 1609;

    return (float) (dist * meterConversion);
}

When user clicks the canvas (for simplicity just imagine it has only one line):

• lineLength = Compute distance between the points (full length of the line)
• endToClickLength1 = Calculate distance from the click position to endpoint 1 of the line
• endToClickLength2 = Calculate distance from the click position to endpoint 2 of the line

Now, if endToClickLength1 + endToClickLength2 = lineLength (+/- acceptedError), then the user has clicked the line.

The acceptedError is needed to widen the boundary for when a lines is clicked a bit.

Do this for all the drawn lines to tell if one of the lines have been clicked.