How do I draw 2D shapes on a model's material

[Bobblehead]

Does anyone have code which accomplishes this? Right now I'm doing this:
local cid_mat = CreateMaterial("cid_model","VertexLitGeneric",{["$basetexture"] = "models/Dorado/1texture"}) --this basetexture is the basetexture used by the model by default.

--this is the operational code:
function model:PreDrawModel(ent)
local base = cid_mat:GetTexture("$basetexture")
render.PushRenderTarget(base,0,0,256,512)
render.Clear(255,255,255,255)
cam.Start2D()
draw.RoundedBox(0,10,10,50,50,color_white) --try to draw a white box. no success.
cam.End2D()
render.PopRenderTarget()
cid_mat:SetTexture("$basetexture",base)

ent:SetMaterial("!cid_model")
end

I'll accept hacky answers too.

[Nak]

Here is how gmod_tool does it: garrysmod/cl_viewscreen.lua at 784cd57576d85712fa13a7cea3a9523b4..
Think you need to use a rendertarget GetRenderTarget( name, width, height)

[Bobblehead]

The toolgun has a dedicated texture just for the screen, so if you overwrite it completely it doesn't fuck up the rest of the model's texture. Any way I can render my stuff on top of the existing texture for my model?

[Bobblehead]

Figured it out. For some reason render.CopyTexture likes to copy the screenspace texture to the destination rather than the one you specify.
I used the following code:
--Items.CID is a DModelPanel.
local cid_mat = Material( "models/Dorado/4texture" )
local rt = CLIENT and GetRenderTarget("cid_texture",256,512,false)
local view = {
type = "3D",
origin = Vector(75,-1,56.5),
angles = Angle(0,180,0),
x = 60,
y = 0,
w = 256,
h = 256,
aspect = 1,
fov = 30,
}
hook.Add("PostRender","cit_cid",function(a,b)
if b then return end
if !IsValid(Items.CID) then return end
CID_MAT_TEX = CID_MAT_TEX or cid_mat:GetTexture("$basetexture") --only load this once since we change it after the first time.

local x,y = Items.CID:LocalToScreen(0,0)
cid_mat:SetTexture("$basetexture",rt)
render.PushRenderTarget(rt,x/ScrW(),y/ScrH(),256,512)
render.Clear(0,0,0,255,true,true)
render.DrawTextureToScreenRect(CID_MAT_TEX,0,0,256,512) --copy default model texture to our RT
cam.Start2D()
surface.SetDrawColor(Color(255,0,0))
surface.SetDrawColor(Color(0,0,0,200))
surface.DrawRect(160,20,70,80)
cam.End2D()

--draw model.
render.SuppressEngineLighting(true)
render.MaterialOverride(nil)
render.ClearDepth()
render.SetScissorRect(160,20,160+70,20+80,true)
cam.Start(view) -- Draw a 3d model.
render.Model({model = LocalPlayer():GetModel(),pos=Vector(0,0,0),ang=Angle(0,0,0)})
cam.End()
render.SetScissorRect(0,0,0,0,false)
render.SuppressEngineLighting(false)
render.PopRenderTarget()
Items.CID.Entity:SetSubMaterial(0,cid_mat:GetName())

-- render.DrawTextureToScreenRect(rt,ScrW()-256,0,256,512) --debug. Renders it on the screen.
end)