A function, that allows more flexibility when rendering text with OpenCV in Python. You can add text outline, draw a list of strings with just one call, and even align the text block horizontally or vertically relative to an anchor point.

opencv_text_rendering.py

import numpy as np
import cv2
from enum import Enum

class Align(Enum):
    LEFT = 0
    CENTER = 1
    RIGHT = 2

class Valign(Enum):
    TOP = 0
    MIDDLE = 1
    BOTTOM = 2
    
class Sorting(Enum):
    NONE = 0
    DSCN = 1
    ASCN = 2
    
def draw_text(canvas, string, org=(0,0), align=Align.LEFT, valign=Valign.TOP, inner_pad=0, outer_pad=[0,0],
              font_face=cv2.FONT_HERSHEY_PLAIN, font_size=2, font_color=(255, 255, 255), font_width=1, line_type=cv2.LINE_4,
              outline=False, outline_color=(0, 0, 0), outline_width=2, darken_background=-1, background_color=None, sort=Sorting.NONE):
    """
    A function for a more sophisticated and flexible text rendering. Using this instead of the standard cv2.putText() may result
    in a small performance loss.
    """

    max_width = 0
    max_height = outer_pad[1] * 2

    if not isinstance(string, list):
        string = [string]

    str_quantity = len(string)

    # list of dimensions
    dims_array = list()

    # iterate through strings to calculate the box dimensions
    for i, s in enumerate(string):

        dims, _ = cv2.getTextSize(s, font_face, font_size, font_width)
        dims_array.append(dims)

        # calculate text block dimensions:
        if dims[0] > max_width:
            max_width = dims[0]
        max_height += dims[1]

        if i > 0 and i < str_quantity:
            max_height += inner_pad

    # set the maximum width of the text block
    max_width = max_width + outer_pad[0] * 2
    
    # if no image was supplied, just return the text block size
    if canvas is None:
        return (max_width, max_height)

    # calculate the top-left point for the text block
    tl = [org[0], org[1]]
    br = [tl[0] + max_width, tl[1] + max_height]

    # horizontal align:
    if align == Align.RIGHT:
        tl[0] = org[0] - max_width
        br[0] = org[0]
    elif align == Align.CENTER:
        tl[0] = org[0] - max_width // 2
        br[0] = org[0] + max_width // 2

    # vertical align:
    if valign == Valign.MIDDLE:
        tl[1] = org[1] - max_height // 2
        br[1] = org[1] + max_height // 2
    elif valign == Valign.BOTTOM:
        tl[1] = org[1] - max_height
        br[1] = org[1]        
    
    if darken_background >= 0:
        darken_background = np.clip(darken_background, 0, 1)
        
    # if necessary, draw a background color
    if background_color is not None and isinstance(background_color, tuple):
        
        if darken_background < 0:
            cv2.rectangle(canvas, (tl[0], tl[1]), (br[0], br[1]), background_color, outline_width)
            cv2.rectangle(canvas, (tl[0], tl[1]), (br[0], br[1]), background_color, -1)
        else:
            overlay = np.zeros(canvas.shape, dtype=canvas.dtype)
            cv2.rectangle(overlay, (tl[0], tl[1]), (br[0], br[1]), background_color, outline_width)
            cv2.rectangle(overlay, (tl[0], tl[1]), (br[0], br[1]), background_color, -1)
            canvas[:] = cv2.addWeighted(canvas, 1.0, overlay, darken_background, 1.0)
    else:
        # if necessary, darken the background of the text by the specified value
        if 0 <= darken_background <= 1:
            canvas[tl[1]:br[1], tl[0]:br[0]] = np.clip(np.uint8(canvas[tl[1]:br[1], tl[0]:br[0]]) * darken_background, 0, 255)

    # sort the text by width, if necessary:
    if sort == Sorting.NONE:
        dims_array = enumerate(dims_array)
    else:
        dims_array = sorted(enumerate(dims_array), key=lambda x: x[1][0], reverse=(sort == Sorting.DSCN))

    # iterate through text lines and draw them:
    for i, (j, dim) in enumerate(dims_array):
        dims = dim
        s = string[j]

        pt = (outer_pad[0] + int(tl[0]), outer_pad[1] + int(tl[1]) + (i+1) * dims[1] + i * inner_pad)

        # draw the outline, when necessary
        if outline:
            cv2.putText(canvas, s, pt, font_face, font_size, outline_color, font_width + outline_width, line_type)

        # draw the string
        cv2.putText(canvas, s, pt, font_face, font_size, font_color[i] if isinstance(font_color, list) else font_color,
                    font_width, line_type)

    # return the total width and height of the text block
    return (max_width, max_height)