Is there a straightforward way to measure the distance between a point and a VectorDrawable group?

Question

In my Android App I want to know the distance between the point where the user clicks and a specific VectorDrawable group.

I want the distance to a group like blue in the VectorDrawable:

<vector android:height="24dp" android:viewportHeight="1052.3622"
    android:viewportWidth="744.0945" android:width="24dp" xmlns:android="http://schemas.android.com/apk/res/android">
    <path android:fillColor="#ff0000"
        android:name="blue"
        android:pathData="M182.9,349.5m-74.7,0a74.7,74.7 0,1 1,149.3 0a74.7,74.7 0,1 1,-149.3 0"
        android:strokeAlpha="1" android:strokeColor="#000000" android:strokeWidth="4.23501825"/>
    <path android:fillColor="#00ff00"
        android:name="red"
        android:pathData="M474.3,392.4a84.3,102.9 0,1 0,168.6 0a84.3,102.9 0,1 0,-168.6 0z"
        android:strokeAlpha="1" android:strokeColor="#000000" android:strokeWidth="5"/>>
</vector>

Is there a straightforward way to calculate this distance in Android?

Answer 1

I am not sure easy method to solve the issue exists but this can be done like this:

Parse vector XML so you have all those variables in runtime. Parsing is not covered here, let's assume you have following data structure that we will work with later:

private static class VectorData {
    private int width = 24;
    private int height = 24;
    private double viewportHeight = 1052.3622;
    private double viewportWidth = 744.0945;
    private String path = "M182.9,349.5m-74.7,0a74.7,74.7 0,1 1,149.3 0a74.7,74.7 0,1 1,-149.3 0";

    private double scaleVectorX(Context context) {
        return dpToPx(context, width) / viewportWidth;
    }

    private double scaleVectorY(Context context) {
        return dpToPx(context, height) / viewportHeight;
    }

    private static float dpToPx(Context context, float dp) {
        return dp * context.getResources().getDisplayMetrics().density;
    }
}

as you see all fields are hardcoded for simplicity.

Next step is to parse vector path data converting it to android.graphics.Path:

android.graphics.Path path = android.util.PathParser.createPathFromPathData(vectorData.path);

android.util.PathParser is not included, but you can find source here: https://android.googlesource.com/platform/frameworks/base/+/17e64ffd852f8fe23b8e2e2ff1b62ee742af17a6/core/java/android/util/PathParser.java. Not sure how legal it is to copy and use it though.

Having path we will need to find N its points (coordinates). More points - more precise result will be and slower processing:

final Collection<Point> points = getPoints(path, iv.getX(), iv.getY(), vectorData);

private static class Point {
    private float x;
    private float y;

    Point(float x, float y) {
        this.x = x;
        this.y = y;
    }

    @Override
    public String toString() {
        return "Point{" +
                "x=" + x +
                ", y=" + y +
                '}';
    }
}

private Collection<Point> getPoints(Path path, float viewX, float viewY, VectorData vectorData) {
    Collection<Point> points = new ArrayList<>();
    PathMeasure pm = new PathMeasure(path, false);
    float length = pm.getLength();
    float distance = 0f;
    int size = N;
    float speed = length / size;
    int counter = 0;
    float[] aCoordinates = new float[2];

    while ((distance < length) && (counter < size)) {
        // get point from the path
        pm.getPosTan(distance, aCoordinates, null);
        float pathX = aCoordinates[0];
        float pathY = aCoordinates[1];

        float x = (float) (vectorData.scaleVectorX(this) * pathX) + viewX;
        float y = (float) (vectorData.scaleVectorY(this) * pathY) + viewY;

        points.add(new Point(x, y));
        counter++;
        distance = distance + speed;
    }

    return points;
} 

path - is our path that we get before, iv - is vector container (ImageView, for example), we need it in order to adjust points coordinates. vectorData - is structure that we got before parsing our vector.

Now we need to define region to handle case where path is closed and we want to treat click inside path as 0 distance:

final Region region = new Region();
RectF rectF = new RectF();
path.computeBounds(rectF, true);
region.setPath(path, new Region((int) rectF.left, (int) rectF.top, (int) rectF.right, (int) rectF.bottom));

In order to calculate min distance following method should be used:

private int getMinDistance(float eventX, float eventY, Collection<Point> pathPoints, Region pathRegion, VectorData vectorData) {
    int minDistance = Integer.MAX_VALUE;

    boolean contains = pathRegion.contains((int) (eventX / vectorData.scaleVectorX(this)), (int) (eventY / vectorData.scaleVectorY(this)));

    if (contains) {
        minDistance = 0;
    } else {
        for (Point point : pathPoints) {
            int distance = getDistanceBetweenPoints((int) eventX, (int) eventY, (int) point.x, (int) point.y);
            if (distance < minDistance) {
                minDistance = distance;
            }
        }
    }
    return minDistance;
}

private int getDistanceBetweenPoints(int x, int y, int x1, int y1) {
    return (int) Math.sqrt((x1 - x) * (x1 - x) + (y1 - y) * (y1 - y));
}