如何绘制衰落路径 [英] How tro draw fading path

问题描述

如何绘制带有淡入淡出(不透明或较粗)线条的Path?像这样的东西.

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

我知道有LinearGradient着色器用于Paint，但不会沿Path弯曲 .

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

一种可能的解决方案是沿Path获取点，然后由我自己通过线段将其绘制出来.但是我也找不到任何方法.

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.

推荐答案

我想到了以下代码. mos重要的事情是

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);
        }
    }
}

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