Coding Style Guide - rockcastle/lvgl GitHub Wiki

File format

Use lv_misc/lv_templ.c and lv_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):
    • 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 than 32 characters
    • Use only very straightforward (e.g. pos: position) or well-established (e.g. pr: press) abbreviations

Coding guide

  • Functions:
    • Try to write function shorter than is 50 lines
    • Always shorter than 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 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. The required config flies are: docs/astyle_c and docs/astyle_h. To format the source files: $ find . -type f -name "*.c" | xargs astyle --options=docs/astyle_c

To format the header files: $ find . -type f -name "*.h" | xargs astyle --options=docs/astyle_h

Append -n to the end to skip creation of backup file OR use $ find . -type f -name "*.bak" -delete (for source file's backups) and find . -type f -name "*.orig" -delete (for header file's backups)
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