Merge pull request #20547 from rogday:gdb_pretty_printer

* add gdb rpetty printer for cv::Mat

* address review comments

doc/tutorials/introduction/linux_gcc_cmake/linux_gcc_cmake.markdown

@@ -1,7 +1,7 @@
 Using OpenCV with gcc and CMake {#tutorial_linux_gcc_cmake}
 ===============================
 
-@prev_tutorial{tutorial_linux_install}
+@prev_tutorial{tutorial_linux_gdb_pretty_printer}
 @next_tutorial{tutorial_linux_eclipse}
 
 |    |    |

doc/tutorials/introduction/linux_gdb_pretty_printer/linux_gdb_pretty_printer.markdown

@@ -0,0 +1,38 @@
+Using OpenCV with gdb-powered IDEs {#tutorial_linux_gdb_pretty_printer}
+=====================
+
+@prev_tutorial{tutorial_linux_install}
+@next_tutorial{tutorial_linux_gcc_cmake}
+
+|    |    |
+| -: | :- |
+| Original author | Egor Smirnov |
+| Compatibility | OpenCV >= 4.0 |
+
+@tableofcontents
+
+# Capabilities {#tutorial_linux_gdb_pretty_printer_capabilities}
+
+This pretty-printer can show element type, `is_continuous`, `is_submatrix` flags and (possibly truncated) matrix. It is known to work in Clion, VS Code and gdb.
+
+![Clion example](images/example.png)
+
+
+# Installation {#tutorial_linux_gdb_pretty_printer_installation}
+
+Move into `opencv/samples/gdb/`. Place `mat_pretty_printer.py` in a convinient place, rename `gdbinit` to `.gdbinit`  and move it into your home folder. Change 'source' line of `.gdbinit` to point to your `mat_pretty_printer.py` path.
+
+In order to check version of python bundled with your gdb, use the following commands from the gdb shell:
+
+    python
+    import sys
+    print(sys.version_info)
+    end
+
+If the version of python 3 installed in your system doesn't match the version in gdb, create a new virtual environment with the exact same version, install `numpy` and change the path to python3 in `.gdbinit` accordingly.
+
+
+# Usage {#tutorial_linux_gdb_pretty_printer_usage}
+
+The fields in a debugger prefixed with `view_` are pseudo-fields added for convinience, the rest are left as is.
+If you feel that the number of elements in truncated view is too low, you can edit `mat_pretty_printer.py` - `np.set_printoptions` controlls everything matrix display-related.

doc/tutorials/introduction/linux_install/linux_install.markdown

@@ -1,7 +1,7 @@
 Installation in Linux {#tutorial_linux_install}
 =====================
 
-@next_tutorial{tutorial_linux_gcc_cmake}
+@next_tutorial{tutorial_linux_gdb_pretty_printer}
 
 |    |    |
 | -: | :- |

doc/tutorials/introduction/table_of_content_introduction.markdown

@@ -6,6 +6,7 @@ Introduction to OpenCV {#tutorial_table_of_content_introduction}
 
 ##### Linux
 -   @subpage tutorial_linux_install
+-   @subpage tutorial_linux_gdb_pretty_printer
 -   @subpage tutorial_linux_gcc_cmake
 -   @subpage tutorial_linux_eclipse