in shared/java/Canvas.java [301:315]
public Canvas drawRectShadow(@NotNull Rect r, float dx, float dy, float blur, float spread, int color) {
assert r != null : "Can’t drawRectShadow with r == null";
Rect insides = r.inflate(-1);
if (!insides.isEmpty()) {
save();
if (insides instanceof RRect)
clipRRect((RRect) insides, ClipMode.DIFFERENCE);
else
clipRect(insides, ClipMode.DIFFERENCE);
drawRectShadowNoclip(r, dx, dy, blur, spread, color);
restore();
} else
drawRectShadowNoclip(r, dx, dy, blur, spread, color);
return this;
}