Get pixel coords for vertex in viewport

Question

Is it possible to get the screen XY coordinates in viewport for a vertex in orthographic view?

I get pixel locations as per a previous answer like this:

co2d = []
for v in cloth.data.vertices:
    p = bpy_extras.object_utils.world_to_camera_view(scene, camera, v.co)
    xy=list(p)
    xy[0] = xy[0] * 680
    xy[1] = xy[1] * 809
    co2d.append(xy)

(image width and height hardcoded here)

Where the camera is defined here:

def area_view_3d():
    areas = [a for a in bpy.context.screen.areas if a.type == "VIEW_3D"]
    if not areas:
        return
    return areas[0]

camera = area_view_3d().spaces[0].camera

but when I take the resulting coordinates and map them onto the screenshot it looks like this:

Clearly I get something that looks like coordinates, but isn't what I want.

What is it that I am getting wrong?

Answer 1

3D location to region 2D

• Instead of using world to camera coords, use the location 3d to region. See How can I show the vertex positions in viewport?

• Have tacked on some bgl to draw a 2D bbox. All verts are used to generate a 2D bounding box from extrema.

Test script.

import bpy
from mathutils import Vector, Matrix
from bpy_extras import view3d_utils
import bmesh
import numpy as np

context = bpy.context
scene = context.scene
ob = context.object
mw = ob.matrix_world
me = ob.data
for a in context.screen.areas:
    if a.type == 'VIEW_3D':
        space = a.spaces.active
        r3d = space.region_3d
        plane_no = r3d.view_rotation @ Vector((0, 0, -1))
        region = a.regions[-1]
        break
else:
   assert False, "Requires a $D view"
        
plane_co = ob.matrix_world.translation

bm = bmesh.new()
bm.from_mesh(me)
bm.transform(ob.matrix_world)
u, v = np.array(
    [view3d_utils.location_3d_to_region_2d(
        region,
        r3d,
        v.co) for v in bm.verts]
        ).T


bbox2d = (
        (u.min(), v.min()),
        (u.max(), v.min()), 
        (u.max(), v.max()),       
        (u.min(), v.max()),
        )
        
#bbox2d = [(0, 0), (100, 0), (100, 100), (0, 100)]
bl, tr = (0, 0), (region.width, region.height)    

import gpu
from gpu_extras.batch import batch_for_shader
from functools import partial

vertices = bbox2d

indices = (
    (0, 1, 2), (2, 3, 0))

shader = gpu.shader.from_builtin('2D_UNIFORM_COLOR')
batch = batch_for_shader(shader, 'TRIS', {"pos": vertices}, indices=indices)


def draw():
    shader.bind()
    shader.uniform_float("color", (0, 1, 1, .10))
    batch.draw(shader)


handle = bpy.types.SpaceView3D.draw_handler_add(draw, (), 'WINDOW', 'POST_PIXEL')


def kill(handle):
    if handle:
        bpy.types.SpaceView3D.draw_handler_remove(handle, 'WINDOW')
    return 0

bpy.app.timers.register(partial(kill, handle), first_interval=2)
a.tag_redraw()