Currently Impeller has two techniques for rendering a shadow:

• Fast RRect/Rect/Circle path that works in a single draw.
• Generic Gaussian Blur 3-Pass

The second case is required for blurring rasters or complex shapes, but is much slower than the fast path. Skia has an intermediate approach, where they compute the tessellated shadow for convex and concave shapes. This is useful in case buttons and such end up non-uniform.

We should devise a similar approach, which as a motivating case can use the application in: #169423

Sources:

• https://github.com/google/skia/blob/b6c161a0f51f7af0749917ddd222f9d297cb076e/src/utils/SkShadowTessellator.cpp#L263