lvgl/docs/CONTRIBUTING.md

Contributing to Littlev Graphics Library

It's glad to see that you are interested in Contributing to LittlevGL!

In this guide you can learn how can you help to develop LittlevGL.

Table Of Content

• Who can contribute?
• How to report an issue?
• How to suggest a feature?
• How to implement a feature?
• Styling guide

Who can contribute?

As graphical interfaces for embedded systems has an increasing relevance today you also might find important to work with a good graphics library. Now - independently from skills, programming level or any personal attributes - you can influence and help the development of Littlev Graphics Library with:

• Report an issue
• Suggest feature
• Fix an issue
• Implement a feature
• Help with testing bugfixes and new features

Please, take a look at CODE_OF_CONDUCT

There are few general rules:

• We use GitHub's issue tracker
• Be kind and respectful. Strating with "Hi" is always a good idea :)
• If somebedy helped you give a feedback.
• One issue should be about one topic. If you have other questions please open a new issue.
• Always create an issue before creating a Pull request to discuss the idea first
• Create small, "digestable" Pull requests.
• Tell your remarks in a structured way. Use paragraphs and the Markdown support of GitHub.
• Be sure you are using the lates version (from master branch)
• Keep in mind LittlevGL should be and should remain:
  • usable on small MCUs as well (think about memory footprint)
  • compilable with "non-standard" tools (like Arduino)
  • the API cleaan and easiy to understand

How to report a bug?

If you found a simple and straightforward bug like:

• misspelling (in comments function/variable names or grammatical issues in comments)
• not handled error cases (negative array index, overflow etc)
• anything else which can be fixed locally with a few lines of code
• or defective documentation

then tell

• where you found the bug (which file/function/variable)
• how can it cause problem
• what is your suggeseted solution if you have

If you faced with something more clomplex like:

• might be simple but you don't know its origin
• affects a whole file, module or even the architecture
• needs deeper discussion

then please

• tell what do you experience
• tell what do you expect to happen
• tell how to reproduce the issue
• provide a simlified code example (better if can be tested with copy-paste)
• attache your lv_conf.h (if you feel it's important)
• logs and long codes should be attached in a file (instead of copying into a comment)

How to suggest a feature?

If you have a good and useful idea open issue to tell it! Please note the followings on suggesting new features:

• What the new feature is about?
• Why/Where/In which case is it useful/helpful/relevant?
• Can you mention real life usecases/examples for the use this feature?
• Can you help in implementing it?

Your suggestion can have 4 possible outcomes:

1. This feature is already exists. In this case you will learn how to achive your goal.
2. You can simply realize it with the current functionality.
3. Although it's a new feature but it would break LittlevGL's platform independent and/or resource minimalist nature.
4. It's really a new feature which would be good to be in LittlevGL. Hurray! In a discussion we figure out the technical details and implementation options. With the knowledge of how to do it somebody can implement the new feature.

Keep in mind if you wouldn't like to do the implementation there is no guarantee that it will be ready in the near future. However if you would like to force it, take a look at this page: Feature request service

How to implement a feature?

In docs/TODO_MINOR.md and docs/TODO_PATCH.md you can see some ideas which are waiting for somebody to realize them! If want to deal with a feature from this files, please start an issue and discusse the details.

The new feature should be in a new branch.

Styling guide

File format

Use lv_misc/lv_templ.c and lv_misc/lv_templ.h

Naming conventions

• Words are sparated by '_'
• In variable and function names use only lower case letters (e.g. height_tmp)
• In enums and defines use only upper case letters (e.g. e.g. MAX_LINE_NUM)
• Global names (API):
  • starts with lv
  • followed by module name: btn, label, style etc.
  • followed by the action (for functions): set, get, refr etc.
  • closed with the subject: name, size, state etc.
• Typedefs
  • prefer typedef struct and typedef enum instead of struct name and enum name
  • always add a closing ..._t
• Abbreviations:
  • Use abbreviations on public names only if they become longer then 32 characters
  • Use only very straightforward (e.g. pos: position) or well established (e.g. pr: press) abbreviatons

Coding guide

• Functions:
  • Try to write function shorter then is 50 lines
  • Always shorter then 100 lines (except very straightforwards)
• Variables:
  • One line, one declaration (BAD: char x, y;)
  • Use <stdint.h> (uint8_t, int32_t etc)
  • Declare variables when needed (not all at function start)
  • Use the smallest required scope
  • Variables in a file (outside functions) are always static
  • Do not use global variables (use functions to set/get static variables)

Comments

Before every function have a comment like this:

/**
 * Return with the screen of an object
 * @param obj pointer to an object
 * @return pointer to a screen
 */
lv_obj_t * lv_obj_get_scr(lv_obj_t * obj); 

Always use /* Something */ format and NOT //Something

Write readable code to avoid descriptive comments like: x++; /* Add 1 to x */. The code should show clearly what you are doing.

You should write why have you done this: x++; /*Because of closing '\0' of the string */

Short "code summaries" of a few lines are accepted. E.g. /*Calculate the new coordinates*/

In comments use ` ` when refering to a variable. E.g. /*Update the value of `x_act`*/

Formatting

Here is example to show bracket placing and using of white spaces:

/**
 * Set a new text for a label. Memory will be allocated to store the text by the label.
 * @param label pointer to a label object
 * @param text '\0' terminated character string. NULL to refresh with the current text.
 */
void lv_label_set_text(lv_obj_t * label, const char * text)
{   /* Main bracket of functions in new line*/
    
    if(label == NULL) return; /*No bracket only if the command is inline with the if statement*/
    
    lv_obj_inv(label);
    
    lv_label_ext_t * ext = lv_obj_get_ext(label);

    /*Comment before a section */
    if(text == ext->txt || text == NULL) {  /*Bracket of statements start inline*/
        lv_label_refr_text(label);
        return;   
    }
    
    ...
}

Use 4 spaces indentation instead of tab.