Shadows Part Deux

[Corey Lucier]

So running into a bit of a performance puzzle with SkDropShadowImageFilter.

See attached image.  We're seeing very slow render times when zoomed in very far (400+%) to our skia surface. As you can tell we're using a tiled (raster) renderer. So each tile clips to it's bounds and renders the rectangle in this case using SkDropShadowImageFilter, and then another pass for the foreground.  

Basic approach per (256x256) tile is :

    Transform viewport to account for zoom

    Clip to tile bounds

    Attach drop shadow filter to Paint

    canvas->saveLayer(nullptr, Paint);

    Draw Rectangle

    canvas->restore()

    Draw Rectangle

Any suggestions on how to make the blur filter faster, or at least this scenario faster?

NOTE: The reason we use a layer here is because we can be drawing any number of things (hierarchy of paths, shapes, etc. with their strokes and fills), not just a single rectangle.

99.9% profiler time is being spent in SkBoxBlur_SSE4.

We can't really cache the shadow per say between frames in this scenario because in this case the user is resizing/morphing the rectangle interactively, so of course the shadow needs to be recomputed.