Lines can't seen with some angle

localPlayer=getLocalPlayer()
local color = tocolor(255,0,255,255)
function getPositionInFrontOfElement(element,x,y,z)
    -- Get the matrix
    local matrix =  getElementMatrix ( element )
    -- Get the transformation of a point 5 units in front of the element
    local offX = x * matrix[1][1] + y * matrix[2][1] + z * matrix[3][1] + matrix[4][1]
    local offY = x * matrix[1][2] + y * matrix[2][2] + z * matrix[3][2] + matrix[4][2]
    local offZ = x * matrix[1][3] + y * matrix[2][3] + z * matrix[3][3] + matrix[4][3]
    --Return the transformed point
    return offX, offY, offZ
end

addEventHandler("onClientPreRender",getRootElement(),function(timeslice)
    local x1,y1,z1 = getPositionInFrontOfElement(localPlayer,6,-6,0)
    local x2,y2,z2 = getPositionInFrontOfElement(localPlayer,6,6,0)
    local x3,y3,z3 = getPositionInFrontOfElement(localPlayer,-6,-6,0)
    local x4,y4,z4 = getPositionInFrontOfElement(localPlayer,-6,6,0)
    local xx,yy,zz = getElementPosition(localPlayer)
    z1 = getGroundPosition(x1,y1,z1)+1
    z2 = getGroundPosition(x2,y2,z2)+1
    z3 = getGroundPosition(x3,y3,z3)+1
    z4 = getGroundPosition(x4,y4,z4)+1
    dxDrawLine3D(x1,y1,z1,x2,y2,z2,color,10,1,1,1)
    dxDrawLine3D(x2,y2,z2,x4,y4,z4,color,10,1,1,1)
    dxDrawLine3D(x3,y3,z3,x1,y1,z1,color,10,1,1,1)
    dxDrawLine3D(x4,y4,z4,x3,y3,z3,color,10,1,1,1)
end)