A u8g2 function like u8glib u8g.drawStrP

[MikeKitchen]

I’m trying to migrate my projects from u8glib to u8g2, but I would like a replacement for u8g.drawStrP with AVR processors using with multiple menus stored in flash memory.

In u8glib you’d use something like :

const u8g_pgm_uint8_t menu0_0[] U8G_PROGMEM  = "String 1";
const u8g_pgm_uint8_t menu0_1[] U8G_PROGMEM  = "String 2";
const u8g_pgm_uint8_t menu0_2[] U8G_PROGMEM  = "String 3";
const u8g_pgm_uint8_t menu0_3[] U8G_PROGMEM  = "String 4";
const u8g_pgm_uint8_t* const menu0_strings[] = {menu0_0, menu0_1, menu0_2, menu0_3};

const u8g_pgm_uint8_t menu0_0[] U8G_PROGMEM  = "Option 1";
const u8g_pgm_uint8_t menu1_1[] U8G_PROGMEM  = "Option 2";
const u8g_pgm_uint8_t menu2_2[] U8G_PROGMEM  = "Option 3";
const u8g_pgm_uint8_t menu3_3[] U8G_PROGMEM  = "Option 4";
const u8g_pgm_uint8_t* const menu1_strings[] = {menu1_0, menu1_1, menu1_2, menu1_3};

//Then

u8g.firstPage();
do {
  u8g.drawStrP(0, 10, menu0_strings[1]); //This prints “String 2”
  u8g.drawStrP(0, 20, menu1_strings[3]); //This prints “Option 4”
} while ( u8g.nextPage() );

I’ve got a near-equivalent working in u8g2, but I was hoping to have a better replacement where I could just cut and paste it in and the below does not seem as elegant as u8glib, is there a better solution?

const char menu0_0[] PROGMEM  = "String 1";
const char menu0_1[] PROGMEM  = "String 2";
const char menu0_2[] PROGMEM  = "String 3";
const char menu0_3[] PROGMEM  = "String 4";
const char *const menu0_strings[] PROGMEM  = {menu0_0, menu0_1, menu0_2, menu0_3};

const char menu1_0[] PROGMEM  = "Option 1";
const char menu1_1[] PROGMEM  = "Option 2";
const char menu1_2[] PROGMEM  = "Option 3";
const char menu1_3[] PROGMEM  = "Option 4";
const char *const menu1_strings[] PROGMEM  = {menu1_0, menu1_1, menu1_2, menu1_3};

//Then

u8g2.firstPage();
do {
  u8g2_drawSringP(0, 10, (char *)pgm_read_word(&(menu0_strings[1]))); //This prints String 2 ”
  u8g2_drawSringP(0, 20, (char *)pgm_read_word(&(menu1_strings[3]))); //This prints “Option 4”
} while ( u8g2.nextPage() );

void u8g2_drawSringP(uint8_t x, uint8_t y, const char * progmem_ptr) {
  char u8g2_buffer[30]; //make the buffer larger than the largest string stored in flash memory

  strcpy_P(u8g2_buffer, (char *) progmem_ptr);  //casts and dereferencing
  u8g2.setCursor(x, y);
  u8g2.print(u8g2_buffer);
}

Thanks for your help

Mike

[olikraus]

Good point. However meanwhile there is a better support for flash memory in Arduino, so maybe this will work:

void u8g2_drawSringP(uint8_t x, uint8_t y, const char * progmem_ptr) {
  u8g2.setCursor(x, y);
  u8g2.print((const __FlashStringHelper *)progmem_ptr);  // use arduino progmem print
}

u8g2.print() is not a u8g2 function, instead it is the same function as used for example for Serial.print(), so there should be support for PROGMEM.

If the above code doesn't work (I have not tested this), then maybe this u8g2 code will work better (also not tested):

void u8g2_drawSringP(uint8_t x, uint8_t y, const char * progmem_ptr) {
  uint16_t c;
  for(;;) {
    c = u8x8_pgm_read(progmem_ptr);  // use u8g2 build-in progmem read function
    if ( c == 0 ) 
      break;
    progmem_ptr++;
   x += u8g2.drawGlyph(x, y, c);
 }
}