How to make GUI dynamic texture?

Questions
2

I have something which I don’t think is ideal:

	self.preview_buf = buffer.create(PREVIEW_WIDTH * PREVIEW_HEIGHT,
		{ { name = hash("rgb"), type = buffer.VALUE_TYPE_UINT8, count = 3 } })
	local tstream = buffer.get_stream(self.preview_buf, hash("rgb"))
	for x = 0, PREVIEW_WIDTH - 1 do
		for y = 0, PREVIEW_HEIGHT - 1 do
			i = 3 * (y * PREVIEW_WIDTH + x) + 1
			tstream[i + 0] = 0x33
			tstream[i + 1] = 0x33
			tstream[i + 2] = 0x33
		end
	end
	if gui.new_texture("preview_tex", PREVIEW_WIDTH, PREVIEW_HEIGHT, "rgb",
			buffer.get_bytes(self.preview_buf, hash("rgb")),
			false) then
		gui.set_texture(self.preview, "preview_tex")
	end

I still have to create a new texture each update. I would prefer not needing that.