Paint a splat layer along the spline footprint (channel + banks) with the
coverage as the blend weight, renormalizing the other layers down — the
"dress the banks" half of a carve. Mutates the arrays in place; returns
the touched SPLAT texel rect or null.
Paint a splat layer along the spline footprint (channel + banks) with the coverage as the blend weight, renormalizing the other layers down — the "dress the banks" half of a carve. Mutates the arrays in place; returns the touched SPLAT texel rect or null.