lvgl/docs/CODING_STYLE.md

Coding style

File format

Use misc/lv_templ.c and misc/lv_templ.h

Naming conventions

• Words are separated 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):
  • start 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 end typedef struct and typedef enum type names with _t
• Abbreviations:
  • Only words longer or equal than 6 characters can be abbreviated.
  • Abbreviate only if it makes the word at least half as long
  • Use only very straightforward and well-known abbreviations (e.g. pos: position, def: default, btn: button)

Coding guide

• Functions:
  • Try to write function shorter than is 50 lines
  • Always shorter than 200 lines (except very straightforwards)
• Variables:
  • One line, one declaration (BAD: char x, y;)
  • Use <stdint.h> (uint8_t, int32_t etc)
  • Declare variables where 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 referring 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 brackets 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.

You can use astyle to format the code. Run code-formatter.sh from the scrips folder.