LLEMU (Legacy LCD Emulator) C API

Note

Additional example code for this module can be found in its Tutorial.

Functions

lcd_clear

Clear the text on the emulated three-button LCD screen.

This function uses the following values of errno when an error state is reached:

  • ENXIO - The LCD has not been initialized. Call lcd_initialize first.

Analogous to pros::lcd::clear.

Prototype
Example
bool lcd_clear ( )

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void initialize() {
  lcd_initialize();
  lcd_set_text(1, "Hello World!");
  lcd_clear(); // No more text will be displayed
}

Returns: true if the operation was successful, or false otherwise, setting errno values as specified above.

lcd_clear_line

Clears a line on the emulated three-button LCD screen.

This function uses the following values of errno when an error state is reached:

  • ENXIO - The LCD has not been initialized. Call lcd_initialize first.
  • EINVAL - The line number specified is not in the range [0-7]

Analogous to pros::lcd::clear_line.

Prototype
Example
bool lcd_clear_line ( int16_t line )

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void initialize() {
  lcd_initialize();
  lcd_set_text(1, "Hello World!");
  lcd_clear_line(1); // No more text will be displayed
}
Parameters  
line The line to clear

Returns: true if the operation was successful, or false otherwise, setting errno values as specified above.

lcd_initialize

Initialize the display to be an emulation of the three-button, UART-based VEX LCD.

Analogous to pros::lcd::intitialize.

Prototype
Example
bool lcd_initialize ( )

void initialize() {
  lcd_initialize();
  lcd_set_text(1, "Hello World!");
}

Returns: true if the LCD was successfully initialized, or false if it has already been initialized.

lcd_is_initialized

Determines whether the emulated three-button LCD has already been initialized.

Analogous to pros::lcd::is_initialized.

Prototype
Example
bool lcd_is_initialized ( )

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void initialize() {
  lcd_initialize();
  printf("Is the LCD initialized? %d\n", lcd_is_initialized());
  // Will Display True
}

Returns: True if the LCD has been initialized or false if not.

lcd_print

Displays a formatted string on the emulated three-button LCD screen

This function uses the following values of errno when an error state is reached:

  • ENXIO - The LCD has not been initialized. Call lcd_initialize first.
  • EINVAL - The line number specified is not in the range [0-7]

Analogous to pros::lcd::print.

Prototype
Example
bool lcd_print ( int16_t line,
                 const char* fmt,
                 ... )

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void initialize() {
  lcd_initialize();
}

void opcontrol {
  while (true) {
    lcd_print(0, "Buttons Bitmap: %d\n", lcd_read_buttons());
    delay(20);
  }
}
Parameters  
line The line on which to display the text [0-7]
fmt Format string
… Optional list of arguments for the format string

Returns: true if the operation was successful, or false otherwise, setting errno values as specified above.

lcd_read_buttons

Reads the button status from the emulated three-button LCD.

The value returned is a 3-bitinteger where 1 0 0 indicates the left button is pressed, 0 1 0 indicates the center button is pressed, and 0 0 1 indicates the right button is pressed. 0 is returned if no buttons are currently being pressed.

Note that this function is provided for legacy API compatibility purposes, with the caveat that the V5 touch screen does not actually support pressing multiple points on the screen at the same time.

Analogous to pros::lcd::read_buttons.

Prototype
Example
uint8_t lcd_read_buttons ( )

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void initialize() {
  lcd_initialize();
}

void opcontrol {
  while (true) {
    printf("Buttons Bitmap: %d\n", lcd_read_buttons());
    delay(20);
  }
}

Returns: The buttons pressed as a bit mask.

lcd_register_btn0_cb

Register a callback function for the leftmost button.

When the leftmost button on the emulated three-button LCD is pressed, the user-provided callback function will be invoked.

Analogous to pros::lcd::register_btn0_cb.

Prototype
Example
void lcd_register_btn0_cb ( lcd_btn_cb_fn_t cb )

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void on_center_button() {
  static bool pressed = false;
  pressed = !pressed;
  if (pressed) {
    lcd_set_text(2, "I was pressed!");
  } else {
    lcd_clear_line(2);
  }
}

void initialize() {
  lcd_initialize();
  lcd_register_btn0_cb(on_center_button);
}
Parameters  
cb An LCD callback function to be executed by this button press

lcd_register_btn1_cb

Register a callback function for the center button.

When the center button on the emulated three-button LCD is pressed, the user-provided callback function will be invoked.

Analogous to pros::lcd::register_btn1_cb.

Prototype
Example
void lcd_register_btn1_cb ( lcd_btn_cb_fn_t cb )

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void on_center_button() {
  static bool pressed = false;
  pressed = !pressed;
  if (pressed) {
    lcd_set_text(2, "I was pressed!");
  } else {
    lcd_clear_line(2);
  }
}

void initialize() {
  lcd_initialize();
  lcd_register_btn1_cb(on_center_button);
}
Parameters  
cb An LCD callback function to be executed by this button press

lcd_register_btn2_cb

Register a callback function for the rightmost button.

When the rightmost button on the emulated three-button LCD is pressed, the user-provided callback function will be invoked.

Analogous to pros::lcd::register_btn2_cb.

Prototype
Example
void lcd_register_btn2_cb ( lcd_btn_cb_fn_t cb )

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void on_center_button() {
  static bool pressed = false;
  pressed = !pressed;
  if (pressed) {
    lcd_set_text(2, "I was pressed!");
  } else {
    lcd_clear_line(2);
  }
}

void initialize() {
  lcd_initialize();
  lcd_register_btn2_cb(on_center_button);
}
Parameters  
cb An LCD callback function to be executed by this button press

lcd_set_text

Displays a string on the emulated three-button LCD screen

This function uses the following values of errno when an error state is reached:

  • ENXIO - The LCD has not been initialized. Call lcd_initialize() first.
  • EINVAL - The line number specified is not in the range [0-7]

Analogous to pros::lcd::set_text.

Prototype
Example
bool lcd_set_text ( int16_t line,
                    const char* text )

void initialize() {
  lcd_initialize();
  lcd_set_text(1, "Hello World!");
}
Parameters  
line The line on which to display the text [0-7]
text The text to display

Returns: true if the operation was successful, or false otherwise, setting errno values as specified above.

lcd_shutdown

Turn off the Legacy LCD Emulator.

Calling this function will clear the entire display, and you will not be able to call any further LLEMU functions until another call to lcd_initialize.

This function uses the following values of errno when an error state is reached:

  • ENXIO - The LCD has not been initialized. Call lcd_initialize first.

Analogous to pros::lcd::shutdown.

Prototype
Example
bool lcd_shutdown ( )

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void initialize() {
  lcd_initialize();
  lcd_set_text(1, "Hello World!");
  lcd_shutdown(); // All done with the LCD
}

Returns: true if the operation was successful, or false otherwise, setting errno values as specified above.

lcd_set_background_color

Changes the color of the LCD background to a provided color expressed in type lv_color_t.

Analogous to pros::lcd::set_background_color.

Prototype
Example
void lcd_set_background_color( lv_color_t color )

void initialize() {
  lcd_initialize();
  lcd_set_background_color(COLOR_GOLD);
}
Parameters  
color A color of type lv_color_t

lcd_set_text_color

Changes the text color of the LCD to a provided color expressed in type lv_color_t.

Analogous to pros::lcd::set_text_color.

Prototype
Example
void lcd_set_text_color( lv_color_t color )

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void initialize() {
  lcd_initialize();
  lcd_set_text_color(COLOR_GOLD);
  lcd_set_text(1, "Hello World!");
}
Parameters  
color A color of type lv_color_t

Macros

LCD_BTN_CENTER

Use LCD_BTN_CENTER as a bitmask for determining if the center LCD button was pressed from lcd_read_buttons.

Value: 2

LCD_BTN_LEFT

Use LCD_BTN_LEFT as a bitmask for determining if the left LCD button was pressed from lcd_read_buttons.

Value: 4

LCD_BTN_RIGHT

Use LCD_BTN_RIGHT as a bitmask for determining if the right LCD button was pressed from lcd_read_buttons.

Value: 1

Typedefs

lcd_btn_cb_fn_t

typedef void (*lcd_btn_cb_fn_t)(void);

A callback function for a button on the LCD.

This will be called each time its corresponding button is pressed.