View cv::Mat in GDB.. Based on https://sourceware.org/legacy-ml/gdb/2013-04/msg00104.html

cv_plotter.py

"""
OpenCV Mat viewer in GDB
"""

import gdb
import cv2
import numpy as np


class PlotterCommand(gdb.Command):
  """
  Plotter command class with gdb command base class
  """
  def __init__(self):
    super(PlotterCommand, self).__init__("plot",
                                         gdb.COMMAND_DATA,
                                         gdb.COMPLETE_SYMBOL)

  def invoke(self, arg, from_tty):
    args = gdb.string_to_argv(arg)
    # generally, we type "plot someimage" in the GDB commandline
    # where "someimage" is an instance of cv::Mat
    v = gdb.parse_and_eval(args[0])
    cmd = ""
    if len(args) > 1:
        cmd = args[1]

    CV_CN_MAX = 512
    CV_CN_SHIFT = 3
    CV_MAT_CN_MASK = (CV_CN_MAX - 1) << CV_CN_SHIFT
    flags = v['flags']

    # Mat.channels() will work only the method is used in the code
    # otherwise the function is not generated for the template
    channel = (((flags) & CV_MAT_CN_MASK) >> CV_CN_SHIFT) + 1
    CV_DEPTH_MAX = (1 << CV_CN_SHIFT)
    CV_MAT_DEPTH_MASK = CV_DEPTH_MAX - 1
    depth = (flags) & CV_MAT_DEPTH_MASK

    if depth == cv2.CV_8U:
      dtype = np.uint8
    elif depth == cv2.CV_8S:
      dtype = np.int8
    elif depth == cv2.CV_16U:
      dtype = np.uint16
    elif depth == cv2.CV_16S:
      dtype = np.int16
    elif depth == cv2.CV_16S:
      dtype = np.int16
    elif depth == cv2.CV_32F:
      dtype = np.float32
    elif depth == cv2.CV_64F:
      dtype = np.float64

    # conver the v['data'] type to "char*" type
    char_type = gdb.lookup_type("char")
    char_pointer_type = char_type.pointer()
    gbuffer = v['data'].cast(char_pointer_type)
    # read bytes from inferior's memory, because
    # we run the opencv-python module in GDB's own process
    # otherwise, we use memory corss processes
    buf = v['step']['buf']
    cbytes = buf[0] * v['rows']  # buf[0] is the step? Not quite sure.
    inferior = gdb.selected_inferior()
    mem = inferior.read_memory(gbuffer, cbytes)

    img = np.frombuffer(mem, dtype)
    if channel != 1:
      img = img.reshape((v['cols'], v['rows'], channel))
    else:
      img = img.reshape((v['rows'], v['cols']))

    if cmd == "":
      cv2.namedWindow('debugger')
      cv2.imshow('debugger', img)

      # the below statement is necessory, otherwise, the Window
      # will hang
      cv2.waitKey(0)
    elif cmd == "print":
      print(img)


PlotterCommand()

Usage: inside gdb
source cv_plotter.py
plot img # displays image in opencv Window
plot img print # prints the image. Useful for seeing pixel values