How tro draw fading path

问题

How can I draw Path with fading (opacity or thicknes) line? Something like this.

I know there is LinearGradient shader for Paint, but it won't bend along the Path.

One possible solution might be to get points along the Path and just draw it by myself through the segments`. But I coouldn't find any method for that either.

回答1:

I came up with the following code. The mos important thing is PathMeasure's getPosTan() method.

if (getGesturePath() != null) {
    final short steps = 150;
    final byte stepDistance = 5;
    final byte maxTrailRadius = 15;
    pathMeasure.setPath(getGesturePath(), false);
    final float pathLength = pathMeasure.getLength();
    for (short i = 1; i <= steps; i++) {
        final float distance = pathLength - i * stepDistance;
        if (distance >= 0) {
            final float trailRadius = maxTrailRadius * (1 - (float) i / steps);
            pathMeasure.getPosTan(distance, pathPos, null);
            final float x = pathPos[0] + RandomUtils.nextFloat(0, 2 * trailRadius) - trailRadius;
            final float y = pathPos[1] + RandomUtils.nextFloat(0, 2 * trailRadius) - trailRadius;
            paint.setShader(new RadialGradient(
                    x,
                    y,
                    trailRadius > 0 ? trailRadius : Float.MIN_VALUE,
                    ColorUtils.setAlphaComponent(Color.GREEN, random.nextInt(0xff)),
                    Color.TRANSPARENT,
                    Shader.TileMode.CLAMP
            ));
            canvas.drawCircle(x, y, trailRadius, paint);
        }
    }
}

来源：https://stackoverflow.com/questions/40396584/how-tro-draw-fading-path