WoWInterface - texture drawing order?

Hi all,

So, I was trying to create a cast bar and reached here to ask a question regarding drawing orders of texture.

Please have a look at the lines of code that I wrote:

Lua Code:

A.CreateCastBar = function(f, unit)
    local point, relativeTo, relativePoint, xOfs, yOfs = unpack(G[unit]["castbar"]["point"]);
 
    local CastBar = CreateFrame("Frame", f:GetName() .. "CastBar", f);
    CastBar:SetSize(G[unit]["castbar"]["width"], G[unit]["castbar"]["height"]);
    CastBar:SetPoint(point, relativeTo, relativePoint, xOfs, yOfs);
 
    local Bar = CreateFrame("StatusBar", nil, CastBar);
    Bar:SetSize(CastBar:GetWidth() - 36, CastBar:GetHeight() - 4);
    Bar:SetPoint("RIGHT", CastBar, "RIGHT", -2, 0);
    Bar:SetStatusBarTexture(BACKDROP);
    Bar:SetStatusBarColor(0.5, 0.5, 1, 1);
 
    CastBar.Bar = Bar;
 
    local bg = Bar:CreateTexture(nil, "BACKGROUND");
    bg:SetAllPoints(true);
    bg:SetTexture(BACKDROP);
    bg:SetVertexColor(1, 1, 1, 1);
 
    CastBar.bg = bg;
 
    local background = Bar:CreateTexture(nil, "BACKGROUND");
    background:SetSize(Bar:GetWidth() + 4, Bar:GetHeight() + 4);
    background:SetPoint("CENTER", Bar, "CENTER", 0, 0);
    background:SetTexture(BACKDROP);
    background:SetVertexColor(0.1, 0.1, 0.1, 1);
 
    CastBar.background = background;
 
    local Icon = CreateFrame("Frame", nil, CastBar);
    Icon:SetSize(CastBar:GetHeight() - 4, CastBar:GetHeight() - 4);
    Icon:SetPoint("LEFT", CastBar, "LEFT", 2, 0);
 
    CastBar.Icon = Icon;
 
    local texture = Icon:CreateTexture(nil, "OVERLAY");
    texture:SetAllPoints(true);
    texture:SetTexture(BACKDROP);
    texture:SetVertexColor(0.5, 0.5, 1, 1);
 
    Icon.texture = texture;
 
    background = Icon:CreateTexture(nil, "BACKGROUND");
    background:SetSize(Icon:GetWidth() + 4, Icon:GetHeight() + 4);
    background:SetPoint("CENTER", Icon, "CENTER", 0, 0);
    background:SetTexture(BACKDROP);
    background:SetVertexColor(0.1, 0.1, 0.1, 1);
 
    Icon.background = background;
end

and my problematic part is here:

Lua Code:

local bg = Bar:CreateTexture(nil, "BACKGROUND");
bg:SetAllPoints(true);
bg:SetTexture(BACKDROP);
bg:SetVertexColor(1, 1, 1, 1);
 
CastBar.bg = bg;
 
local background = Bar:CreateTexture(nil, "BACKGROUND");
background:SetSize(Bar:GetWidth() + 4, Bar:GetHeight() + 4);
background:SetPoint("CENTER", Bar, "CENTER", 0, 0);
background:SetTexture(BACKDROP);
background:SetVertexColor(0.1, 0.1, 0.1, 1);
 
CastBar.background = background;

Since "bg" and "background" are drawn on same layer, it does not draw "bg" on screen.

Any helps please?