Construct a rounded rectangle from its left, top, right, and bottom edges, and the same radii along its horizontal axis and its vertical axis.
Source
RRect.fromLTRBXY(double left, double top, double right, double bottom,
double radiusX, double radiusY) {
_value
..[0] = left
..[1] = top
..[2] = right
..[3] = bottom
..[4] = radiusX
..[5] = radiusY
..[6] = radiusX
..[7] = radiusY
..[8] = radiusX
..[9] = radiusY
..[10] = radiusX
..[11] = radiusY;
}