path: root/HACKING

This file's purpose is to guide contributors and developers to help on the
digiKam project.

========================================================================
10 golden rules for starting with open source
========================================================================

Before to contribute to digiKam project, please take a look to this link:

http://schlitt.info/applications/blog/index.php?/archives/541-10-golden-rules-for-starting-with-open-source.html

========================================================================
Source code formatting:
========================================================================

Adhere to this style guide strictly while adding new code to digiKam or 
working on existing code. 

-------------------------------------------------------------------------
* Indentation length
-------------------------------------------------------------------------

Indent with 4 spaces exactly.

for eg:

void function()
{
....int a;                    // 4 spaces from beginning
....for (int i=0; i<10; i++)  // 4 spaces from beginning
....{                         // 4 spaces from beginning
........a = i;                // 4 spaces from previous indent block

Emacs by default will indent to 4 spaces
vim users add this to you .vimrc
 set tabstop=4        

-------------------------------------------------------------------------
* Tabs vs Spaces
-------------------------------------------------------------------------

Absolutely no tabs. Use a sensible editor which will convert tabs to spaces. 
This will reduce unnecessary changes in your cvs commits.

Emacs by default will convert tab to spaces.
For vim users, add this to your .vimrc
  set expandtab

-------------------------------------------------------------------------
* Line length
-------------------------------------------------------------------------

Line length should never exceed 80 chars (unless really necessary - these 
cases are rare). Having long lines greatly reduces readability of code

-------------------------------------------------------------------------
* Bracketing
-------------------------------------------------------------------------

In almost all cases, {} brackets should start on a newline and should be 
aligned with previous line (follow the indentation spaces). for eg.

class A 
{ //new line
...

for (int i=0; i<10; i++)
{ //new line

if (a == foobar)
{ //new line
... 
}
else
{ // new line
..
} 

-------------------------------------------------------------------------
* Positioning of Access modifiers
-------------------------------------------------------------------------

public, private, protected, public slots, ... should be aligned to the 
beginning of the line with no margin

class A
{
public: // aligned to left 
...
private slots: // aligned to left 


Follow a consistent order in defining these attributes. The recommended
order is public, protected (functions), private (functions), 
signals, public slots, protected slots, private slots, private (variables)

========================================================================
Class, file and Variable names:
========================================================================

-------------------------------------------------------------------------
* Class and filenames
-------------------------------------------------------------------------

- filenames should always be in lower-case 
- class names should match the filenames. Capitalize the first letter and
  other letters logically to improve readability

-------------------------------------------------------------------------
* Protected Member variables
-------------------------------------------------------------------------

- protected member variable names should always be of the form m_varName. 
- Captilize logically so that it becomes easy to read it. Do not capitalize
  the first letter after _ (Use m_varName not m_VarName)
- variable names should be indicative of their functionality and also of 
  the type they belong too if they are instances of qt widgets.
  for eg, QCheckBox* m_autoRotateCheckBox;

-------------------------------------------------------------------------
* Non-Member variables
-------------------------------------------------------------------------

- non-member variables should follow the same naming convention as the member 
  variables, except for the leading m_

-------------------------------------------------------------------------
* Private Member variables
-------------------------------------------------------------------------

- private member variables must be stored in a d private container to reduce
  compilation time and improve binary compatibilty between digiKam components.
  See more informations how to use a 'd' private class at this url: 

  http://developer.kde.org/policies/librarypolicy.html

========================================================================
Comments and Whitespace
========================================================================

Use whitespaces liberally to improve readability. Add blank lines between logical
sections of the code.

Comment as much as possible. Position comments at the beginning of the
section/line you want to comment, NEVER at the end of the line

// put your comments here
a = (b == foobar) ? 1 : -1; 

a = (b == foobar) ? 1 : -1; // you are asking for trouble by putting comments here


========================================================================
Header files
========================================================================

- Add copyright to top of every file. Use the same header than others digiKam
  source code.
- Double inclusion protection defines are all upper case letters and are 
  composed of the classname and a H suffix separated by underscore

#ifndef ANOTHERNICECLASS_H
#define ANOTHERNICECLASS_H

class AnotherNiceClass
{
...
}

#endif

- Use forward declarations as much as possible.

class QFileInfo;

class A
{
....QFileInfo* m_fileInfo;

========================================================================
General recommendations
========================================================================

Please take a look into KDE contrib page tips before to write code/patches for 
digiKam project : http://techbase.kde.org/Contribute

Use the same .cpp/.h header than the rest of digiKam project.

Use a decent editor which does auto-indentation/syntax-highlighting for you. 
I personally use Emacs (Renchi) or Kdevelop (Gilles).
There are excellent initializer scripts in the tdesdk
package for xemacs and vim which can substantially increase your productivity.

Just to give a taste of what i can do with emacs (and tdesdk):

* automatically insert copyright (and ifdefs) in new files.
* insertion of class function definitions for declared class 
  functions in header with one keystroke
* switch between header and declaration files with one keystroke
* go to corresponding definition/declaration with one keystroke
* tab completion of variable/function names already declared.

========================================================================
GDB Backtrace 
========================================================================

If you found a context to crash digiKam, you can provide a backtrace using GDB debugger.
digiKam need to be compiled with all debug info else the backtrace will not suitable.
There is a configure option for that:

# make -f Makefile.cvs
# ./configure --enable-debug=full
# make
# su
# make install.

To make a backtrace with GDB use following command:

# gdb digikam
> run
> ...
> _crash here_
> ...
> bt
> _the backtrace is here_
> quit

Post this backtrace at the right place (B.K.O or devel ML) for investigations by developers.

========================================================================
Memory leak 
========================================================================

To check any memory leak problem in digiKam, valgrind is your friend (http://valgrind.org)
Try this command line to use with valgrind :

valgrind --tool=memcheck --leak-check=full --error-limit=no digikam

========================================================================
Profiling with cachegrind
========================================================================

Valgrind also includes a tool to find out in which parts of your code time is spent.

valgrind --tool=callgrind digikam

Profiling can be disabled at startup to limit the output to the code you are interested in.
Start with

valgrind --tool=callgrind --instr-atstart=no digikam

and prepare the situation you want to profile. Then, in another console, start profiling with
"callgrind_control -i on" and, after the situation has passed, request a profile dump with
"callgrind_control -d".
The resulting callgrind.out files need to be viewed with the tdecachegrind program, e.g.:

tdecachegrind callgrind.out.16693.1

=================================================================================
API Documentation Validation, User Documentation Validation, Source Code Checking
=================================================================================

The following site check on a dayly basis for the a.m. errors:
www.englishbreakfastnetwork.org/krazy/

It can be very useful, in particular before major releases.
Don't trust it blindly! Sometimes they propose too advanced modifications that are no compatible with the prevailant include files.

========================================================================
Usability issues
========================================================================

OpenUsability project has define default menu structure and keyboard shortcuts:

http://wiki.openusability.org/guidelines/index.php/Appendices:Keyboard_Shortcuts

========================================================================
Generate API documentation
========================================================================

To generate API documentation, you need to install:

- Doxygen program (http://www.doxygen.org).
- Dot program (http://www.graphviz.org)

Go to 'project' sub-folder and just run doxygen binary program. A new subfolder 
named 'api' will be create. Warning, this can take a while.