Scroll too long strings on bootscreen

Marlin/ultralcd_implementation_hitachi_HD44780.h

 unsigned lcd_print(char c) { return charset_mapper(c); }
 
 #if ENABLED(SHOW_BOOTSCREEN)
+  void lcd_erase_line(int line) {
+    lcd.setCursor(0, 3);
+    for (int i=0; i < LCD_WIDTH; i++)
+      lcd_print(' ');
+  }
+
+  // scrol the PSTR'text' in a 'len' wide field for 'time' milliseconds at position col,line
+  void lcd_scroll(int col, int line, const char * text, int len, int time) {
+    int l = lcd_strlen_P(text);
+    char tmp[LCD_WIDTH+1] = {0};
+    int n = l - len;
+    int t = time / ((n>1) ? n: 1);
+    for (int i = 0; i <= (((n-1)>0) ? n-1 : 0); i++) {
+      strncpy_P(tmp, text+i, min(len, LCD_WIDTH));
+      lcd.setCursor(col, line);
+      lcd_print(tmp);
+      delay(t);
+    }
+  }
+
   static void bootscreen() {
     show_bootscreen = false;
     byte top_left[8] = {
        lcd_printPGM(PSTR(STRING_SPLASH_LINE1));
     #endif
     lcd.setCursor(0, 2); lcd.print('\x02'); lcd_printPGM(PSTR( "------"));  lcd.print('\x03');
-    lcd.setCursor(0, 3);                    lcd_printPGM(PSTR("marlinfirmware.org"));
-    delay(2000);
+
+    lcd_scroll(0, 3, PSTR("www.marlinfirmware.org" " "), LCD_WIDTH, 2000);
 
     #if (LCD_WIDTH <= 16) && defined(STRING_SPLASH_LINE1)
-      lcd.setCursor(0, 3);
-      lcd_printPGM(PSTR("                  "));
-      lcd.setCursor(0, 3);
-      lcd_printPGM(PSTR(STRING_SPLASH_LINE1));
-      delay(1000);
+      lcd_erase_line(3);
+      lcd_scroll(0, 3, PSTR(STRING_SPLASH_LINE1 " "), LCD_WIDTH, 1000);
     #endif
-
     #ifdef STRING_SPLASH_LINE2
-      lcd.setCursor(0, 3);
-      lcd_printPGM(PSTR("                  "));
-      lcd.setCursor(0, 3);
-      lcd_printPGM(PSTR(STRING_SPLASH_LINE2));
-      delay(1000);
+      lcd_erase_line(3);
+      lcd_scroll(0, 3, PSTR(STRING_SPLASH_LINE2 " "), LCD_WIDTH, 1000);
     #endif
   }
 #endif // SHOW_BOOTSCREEN