local W, H = 128, 128
local tex = GetRenderTarget(
    "something_" .. RealTime(), -- debug
    W,
    H,
    true
)

local function UpdateRenderTarget()
    local old_rt, old_w, old_h = render.GetRenderTarget(), ScrW(), ScrH()
    render.SetRenderTarget(tex)
    render.SetViewPort(0, 0, W, H)
    cam.Start2D()
        --surface.SetDrawColor(100, 100, 100, 100)
        --surface.DrawRect(0, 0, W, H)
        render.Clear(0, 0, 0, 0, true)

        local T = RealTime()

        surface.SetDrawColor(HSVToColor(T*30 % 360, 1, 1))
        surface.DrawRect(W/2 + math.sin(T)*W/4, H/2 + math.cos(T)*H/4, 16, 16)
    cam.End2D()
    render.SetRenderTarget(old_rt)
    render.SetViewPort(0, 0, old_w, old_h)
end

-- update our render target with 10 fps
timer.Create("RT_Update", 1/10, 0, function()
    UpdateRenderTarget()
end)


-- draw it onto our hud
local mat = CreateMaterial("asdf_" .. RealTime(), "UnlitGeneric", {})
mat:SetTexture("$basetexture", tex)

hook.Add("HUDPaint", "asdf", function()
    surface.SetMaterial(mat)
    surface.SetDrawColor(color_white)
    surface.DrawTexturedRect(0, 0, 128, 128)
end)

-- draw it onto a model
local mat = CreateMaterial("asdf_" .. RealTime(), "VertexLitGeneric", {})
mat:SetTexture("$basetexture", tex)

SafeRemoveEntity(rt_ent)
rt_ent = ClientsideModel("models/hunter/plates/plate1x1.mdl")
rt_ent:SetPos(here)
rt_ent.RenderOverride = function(s)
    render.SetBlend(0.99) -- this activates transparency

    render.MaterialOverride(mat)
        s:DrawModel()
    render.MaterialOverride()

    render.SetBlend(1)
end