1、外阴影
外阴影Path：根据图形Path偏移量offsetX，offsetY获得；
描边外阴影，图片的透明没有阴影；
外阴影Paint : 高斯模糊值sigmaX，sigmaY， 填充颜色值
sigmaX,sigmaY，前端过来数据以后有2倍关系；？
透明度为0，外阴影没有；
link : https : //fiddle.skia.org/c/c64f77aa06a1634ef2f6833248e5bf86

 void draw(SkCanvas *canvas){
    //基础数据
    const int offsetX = 10;
    const int offsetY = 10;
    const int sigmaX = 10;
    const int sigmaY = 10;
    SkPoint rectPts[] = {{64, 48}, {192, 160}};
    SkRect rect;
    rect.set(rectPts[0], rectPts[1]);
    SkPath path;
    path.addRect(rect);

    //-----------------------------------------
    //外阴影绘制
    SkPath dropShadowPath = path;
    SkPaint dropShadowPaint;
    dropShadowPaint.setAntiAlias(true);
    dropShadowPaint.setStyle(SkPaint::kStrokeAndFill_Style);
    dropShadowPaint.setColor(SK_ColorBLUE);
    dropShadowPaint.setImageFilter(SkImageFilters::Blur(sigmaX, sigmaY, nullptr, nullptr));
    SkMatrix mat;
    mat.postTranslate(offsetX, offsetY);
    dropShadowPath.transform(mat);
    canvas->drawPath(dropShadowPath, dropShadowPaint);

    //---------------------------------------

    //原始图形绘制
    SkPaint paint;
    paint.setAntiAlias(true);
    paint.setStyle(SkPaint::kStrokeAndFill_Style);
    paint.setColor(SK_ColorRED);
    canvas->drawPath(path, paint);
    //---------------------------------------
}

外阴影效果

2.内阴影
内阴影Path：根据图形Path偏移量offsetX，offsetY获得一个偏移Path2，然后Path与Path2做kDifference_Op运算，求得内阴影innerShadowPath；
内阴影Paint : 高斯模糊值sigmaX，sigmaY， 填充颜色值；
link : https : //fiddle.skia.org/c/17b7d8076d7ef84c0f1a0fa494259388

void draw(SkCanvas *canvas){

    //基础数据
    const int offsetX = 10;
    const int offsetY = 10;
    const int sigmaX = 10;
    const int sigmaY = 10;
    const int gaussianSigma = 200;
    SkPoint rectPts[] = {{64, 48}, {192, 160}};
    SkRect rect;
    rect.set(rectPts[0], rectPts[1]);
    SkPath path;
    path.addRect(rect);
    //-----------------------------------------
    canvas->clipPath(path, true);

    //原始图形绘制
    SkPictureRecorder recorder;
    SkCanvas *recordingCanvas = recorder.beginRecording(rect);
    SkPaint paint;
    paint.setAntiAlias(true);
    paint.setStyle(SkPaint::kStrokeAndFill_Style);
    paint.setColor(SK_ColorRED);
    recordingCanvas->drawPath(path, paint);
    sk_sp<SkPicture> playback = recorder.finishRecordingAsPicture();
    canvas->drawPicture(playback);
    //---------------------------------------

    //内阴影绘制
    SkPath offsetPath = path;
    SkMatrix mat;
    mat.postTranslate(offsetX, offsetY);
    offsetPath.transform(mat);
    SkPath innerShadowPath;
    {

        //OP(path, offsetPath, SkPathOp::kDifference_SkPathOp, &innerShadowPath);
        SkRegion region;
        SkRect pathBounds = path.computeTightBounds();
        SkIRect iRect = SkIRect::MakeLTRB(pathBounds.fLeft, pathBounds.fTop, pathBounds.fRight,
                                          pathBounds.fBottom);
        SkRegion shapeRegion(iRect);
        region.setPath(path, shapeRegion);
        SkRegion _region;
        SkRect pathBounds2 = offsetPath.computeTightBounds();
        SkIRect iRect2 = SkIRect::MakeLTRB(pathBounds2.fLeft, pathBounds2.fTop, pathBounds2.fRight,
                                           pathBounds2.fBottom);

        SkRegion shapeRegion2(iRect2);
        bool flag = _region.setPath(offsetPath, shapeRegion2);
        region.op(_region, SkRegion::Op::kDifference_Op);
        region.getBoundaryPath(&innerShadowPath);
    }

    SkPaint innerShadowPaint;
    innerShadowPaint.setAntiAlias(true);
    innerShadowPaint.setStyle(SkPaint::kStrokeAndFill_Style);
    innerShadowPaint.setColor(SK_ColorBLUE);
    innerShadowPaint.setImageFilter(SkImageFilters::Blur(sigmaX, sigmaY, nullptr, nullptr));
    canvas->drawPath(innerShadowPath, innerShadowPaint);
    //---------------------------------------
}

内阴影效果

3.高斯模糊
高斯模糊SkPicture：录制当前图层的Picture；
高斯模糊Paint : 高斯模糊值sigmaX，sigmaY；
link : https : //fiddle.skia.org/c/a62c64dc9afedeb0f5cf13bdebf68fdf

void draw(SkCanvas *canvas){

    //基础数据
    const int offsetX = 10;
    const int offsetY = 10;
    const int sigmaX = 10;
    const int sigmaY = 10;
    SkPoint rectPts[] = {{64, 48}, {192, 160}};
    SkRect rect;
    rect.set(rectPts[0], rectPts[1]);
    SkPath path;
    path.addRect(rect);

    //-----------------------------------------

    //原始图形绘制
    SkPictureRecorder recorder;
    SkCanvas *recordingCanvas = recorder.beginRecording(rect);
    SkPaint paint;
    paint.setAntiAlias(true);
    paint.setStyle(SkPaint::kStrokeAndFill_Style);
    paint.setColor(SK_ColorRED);
    recordingCanvas->drawPath(path, paint);
    paint.setColor(SK_ColorBLUE);
    SkMatrix mat;
    mat.postTranslate(20, 20);
    path.transform(mat);
    recordingCanvas->drawPath(path, paint);
    sk_sp<SkPicture> playback = recorder.finishRecordingAsPicture();

    //---------------------------------------

    //图层绘制
    SkPaint layerPaint;
    layerPaint.setAntiAlias(true);
    layerPaint.setStyle(SkPaint::kStrokeAndFill_Style);
    //layerPaint.setColor(SK_ColorBLUE);
    layerPaint.setImageFilter(SkImageFilters::Blur(sigmaX, sigmaY, nullptr, nullptr));
    canvas->drawPicture(playback, nullptr, &layerPaint);
    //---------------------------------------
}

高斯模糊效果

4.背景模糊
依赖参数
图层的穿透混合模式
背景模糊SkPicture：录制当前图层的Picture；
背景模糊Paint: 高斯模糊值gaussianSigma；
背景模糊的透明度：Alpha；
link:https://fiddle.skia.org/c/68d1cf656fc6473146e7cb5d80426365

void draw(SkCanvas *canvas){

    //基础数据
    const int offsetX = 10;
    const int offsetY = 10;
    const int gaussianSigma = 200;
    SkPoint rectPts[] = {{64, 48}, {192, 160}};
    SkRect rect;
    rect.set(rectPts[0], rectPts[1]);
    SkPath path;
    path.addRect(rect);

    //底图绘制---------------------------------
    {
        SkPaint paint;
        paint.setAntiAlias(true);
        paint.setStyle(SkPaint::kStrokeAndFill_Style);
        paint.setColor(SK_ColorYELLOW);
        canvas->drawCircle(100, 120, 30, paint);
    }

    //-----------------------------------------
    //原始图形绘制

    SkPictureRecorder recorder;
    SkCanvas *recordingCanvas = recorder.beginRecording(rect);
    SkPaint paint;
    paint.setStyle(SkPaint::kStrokeAndFill_Style);
    paint.setColor(SK_ColorRED);
    recordingCanvas->drawPath(path, paint);
    sk_sp<SkPicture> playback = recorder.finishRecordingAsPicture();

    //---------------------------------------

    //图层绘制
    SkPaint layerPaint;
    layerPaint.setAlpha(255 * 0.4);
    //SkMaskFilter: https://fiddle.skia.org/c/a92b2945009a7d5045248a4fc24122f9

    layerPaint.setMaskFilter(SkMaskFilter::MakeBlur(kInner_SkBlurStyle, gaussianSigma));
    canvas->drawPicture(playback, nullptr, &layerPaint);

    //---------------------------------------
}

背景模糊效果