add zBias setting; remove zIndex from UI and add zBias to UI
add zBias setting; remove zIndex from UI and add zBias to UI

stardust66/math3d,stardust66/math3d,ChristopherChudzicki/math3d,ChristopherChudzicki/math3d,ChristopherChudzicki/math3d,stardust66/math3d,stardust66/math3d,ChristopherChudzicki/math3d