cvplot.py

#filename: cvplot.py
#from: https://sourceware.org/ml/gdb/2013-04/msg00104.html
import gdb
import cv2.cv as cv
import sys
#from subprocess import call

class PlotterCommand(gdb.Command):
    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])
        
        # the value v is a gdb.Value object of C++
        # code's cv::Mat, we need to translate to
        # a python object under cv2.cv
        image_size =  (v['cols'],v['rows'])
        # print v
        # these two below lines do not work. I don't know why
        # channel = gdb.execute("call "+ args[0] + ".channels()", False, True)
        # channel = v.channels();
        CV_8U =0
        CV_8S =1
        CV_16U=2
        CV_16S=3
        CV_32S=4
        CV_32F=5
        CV_64F=6
        CV_USRTYPE1=7
        CV_CN_MAX = 512
        CV_CN_SHIFT = 3
        CV_MAT_CN_MASK = (CV_CN_MAX - 1) << CV_CN_SHIFT
        flags = v['flags']
        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
        IPL_DEPTH_SIGN = 0x80000000
        cv_elem_size = (((4<<28)|0x8442211) >> depth*4) & 15
        if (depth == CV_8S or depth == CV_16S or depth == CV_32S):
                mask = IPL_DEPTH_SIGN
        else:
                mask = 0
        ipl_depth = cv_elem_size*8 | mask     
        img = cv.CreateImageHeader(image_size, ipl_depth, channel)

        # conver the v['data'] type to "char*" type
        char_type = gdb.lookup_type("char")
        char_pointer_type =char_type.pointer()
        buffer = 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']
        bytes = buf[0] * v['rows'] # buf[0] is the step? Not quite sure.
        inferior = gdb.selected_inferior()
        mem = inferior.read_memory(buffer, bytes)

        # set the img's raw data
        cv.SetData(img, mem)

        # create a window, and show the image
        cv.StartWindowThread()
        cv.NamedWindow('viewer')
        cv.ShowImage('viewer', img)

        # the below statement is necessory, otherwise, the Window
        # will hang
        cv.WaitKey(0)
        cv.DestroyWindow('viewer')

        # save matrix as an xml file and open it with matrix viewer
        # cv.Save("/tmp/dump.xml", img, "matrix")
        # call(["matrix-viewer", "/tmp/dump.xml"])
        # cv.SaveImage("/tmp/viewer.png", img)
        # call(["matrix-viewer", "/tmp/viewer.png"])
        
PlotterCommand()