draw text always face the viewer in 3D view

Question

I'd like to write a script to draw some text in 3D view, and I need it always face the viewer, how can I achieve this?

update: My own answer as below.

What have you got so far? Where are you stuck and what didn't work as expected? — Duarte Farrajota Ramos, Mar 16 '17 at 17:32
Do you expect someone to write a script for you, or have you started working on one? It would be useful if you share what you have so far, and explain what precisely is giving you trouble. — Timaroberts, Mar 17 '17 at 00:35
@DuarteFarrajotaRamos Sorry for my unclear question, I've update it. — NGE, Mar 17 '17 at 02:32
You should post that as an answer bellow instead, preferably with a short description of what you did wrong, and how you fixed it. — Duarte Farrajota Ramos, Mar 17 '17 at 02:55
@DuarteFarrajotaRamos OK, but any clue of the documentation for types.SpaceView3D.draw_handler_add()? — NGE, Mar 17 '17 at 03:08
No, Official info seems to be missing https://docs.blender.org/api/blender_python_api_current/bpy.types.SpaceView3D.html#bpy.types.SpaceView3D.draw_handler_add — Duarte Farrajota Ramos, Mar 17 '17 at 04:23

score 4 · Accepted Answer · edited Mar 25 '17 at 17:11

Thank you for all of you comments, and sorry for my rough question.

But I guess I have found the answer:

I've used wrong arguement for the bpy.types.SpaceView3D.draw_handler_add() function. 'POST_PIXEL' shold be used here as the 4th argument, but 'POST_VIEW' was used. I guess 'POST_PIXEL' is for 2D text, and 'POST_VIEW' is for 3D text.

Code and screenshoot as below:

import blf
import bgl
import bpy

RED = (1.0, 0.0, 0.0)
GREEN = (0.0, 1.0, 0.0)

position_1 = (50, 50, 0)
position_2 = (0, 0, 0)

def draw(position, color):
    blf.position(0, *position)
    blf.size(0, 20, 72)
    bgl.glColor3f(*color)
    blf.draw(0, "hello,world")

_handle = bpy.types.SpaceView3D.draw_handler_add(draw, (position_1, RED), 'WINDOW', 'POST_PIXEL')
_another_handle = bpy.types.SpaceView3D.draw_handler_add(draw, (position_2, GREEN), 'WINDOW', 'POST_VIEW')

update:

I've asked someone in our community, and I was given some tips about the 3rd argument, which maybe represent for region type and enumerate in 'WINDOW', 'HEADER', 'CHANNELS', 'TEMPORARY', 'UI', 'TOOLS', 'TOOL_PROPS', 'PREVIEW'.

Code and screenshoot as below for your reference:

import blf
import bgl
import bpy

RED = (1.0, 0.0, 0.0)
GREEN = (0.0, 1.0, 0.0)
BLUE = (0.0, 0.0, 1.0)

position_1 = (0, 0, 0)

def draw(position, color, text):
    blf.position(0, *position)
    blf.size(0, 20, 72)
    bgl.glColor3f(*color)
    blf.draw(0, text)

_handle_1 = bpy.types.SpaceView3D.draw_handler_add(draw, (position_1, RED, 'WINDOW'), 'WINDOW', 'POST_PIXEL')
_handle_2 = bpy.types.SpaceView3D.draw_handler_add(draw, (position_1, GREEN, 'HEADER'), 'HEADER', 'POST_PIXEL')
_handle_3 = bpy.types.SpaceView3D.draw_handler_add(draw, ((100, 0, 0), BLUE, 'CHANNELS'), 'CHANNELS', 'POST_PIXEL')
_handle_4 = bpy.types.SpaceView3D.draw_handler_add(draw, ((250, 0, 0), RED, 'TEMPORARY'), 'TEMPORARY', 'POST_PIXEL')
_handle_5 = bpy.types.SpaceView3D.draw_handler_add(draw, (position_1, GREEN, 'UI'), 'UI', 'POST_PIXEL')
_handle_6 = bpy.types.SpaceView3D.draw_handler_add(draw, (position_1, BLUE, 'TOOLS'), 'TOOLS', 'POST_PIXEL')
_handle_7 = bpy.types.SpaceView3D.draw_handler_add(draw, (position_1, RED, 'TOOL_PROPS'), 'TOOL_PROPS', 'POST_PIXEL')
_handle_8 = bpy.types.SpaceView3D.draw_handler_add(draw, ((400, 0, 0), GREEN, 'PREVIEW'), 'PREVIEW', 'POST_PIXEL')
_handle_1 = bpy.types.SpaceView3D.draw_handler_add(draw, (position_1, RED, 'WINDOW'), 'WINDOW', 'POST_VIEW')

But I‘m still confused about the draw_handler_add funciton. I've read the api documentation for this, but is shows "Undocumented". Anyone can help me, or explain it for me?

I'm sure you've got this figured out by now, but I think this link would be handy here. By calling draw_handler_add you are providing the instructions which are used every time the SpaceView3D needs to be redrawn ( due to a zoom, pan, window resize etc ). The problem then becomes how to cancel these instructions. — JJones, Oct 06 '19 at 10:13

draw text always face the viewer in 3D view

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