source: rtos_arduino/trunk/arduino_lib/libraries/Robot_Control/examples/explore/R09_Picture_Browser/R09_Picture_Browser.ino@ 136

/* Picture Browser

 You can make your own gallery/picture show with the
 Robot. Put some pictures on the SD card, start the
 sketch, they will diplay on the screen.

 Use the left/right buttons to navigate through the
 previous and next images.

 Press up or down to enter a mode where you change
 the pictures by rotating the robot.

 You can add your own pictures onto the SD card, and
 view them in the Robot's gallery!

 Pictures must be uncompressed BMP, 24-bit color depth,
 160 pixels wide, and 128 pixels tall.

 They should be named as "picN.bmp". Replace 'N' with a
 number between 0 and 9.

 The current code only supports 10 pictures. How would you
 improve it to handle more?

 Circuit:
 * Arduino Robot

 created 1 May 2013
 by X. Yang
 modified 12 May 2013
 by D. Cuartielles

 This example is in the public domain
 */

#include <ArduinoRobot.h> // include the robot library
#include <Wire.h>
#include <SPI.h>

const int NUM_PICS = 4;  //Total number of pictures in Gallery

// name the modes
const int CONTROL_MODE_KEY = 0;
const int CONTROL_MODE_COMPASS = 1;

char buffer[] = "pic1.bmp";  // current file name
int i = 1;  // Current gallery sequence counter
int mode = 0;  // Current mode

// text to display on screen
char modeNames[][9] = { "keyboard", "tilt    " };

void setup() {
  // initialize the Robot, SD card, display, and speaker
  Robot.beginSD();
  Robot.beginTFT();
  Robot.begin();

  // draw "lg0.bmp" and "lg1.bmp" on the screen
  Robot.displayLogos();

  // draw init3.bmp from the SD card on the screen
  Robot.drawBMP("init3.bmp", 0, 0);

  // display instructions
  Robot.stroke(0, 0, 0);
  Robot.text("The gallery\n\n has 2 modes, in\n keyboard mode, L/R\n key for switching\n pictures, U/D key\n for changing modes", 5, 5);
  delay(6000);
  Robot.clearScreen();
  Robot.drawBMP("pb.bmp", 0, 0);
  Robot.text("In tilt mode,\n quickly tilt the\n robot to switch\n pictures", 5, 5);
  delay(4000);
}

void loop() {
  buffer[3] = '0' + i; // change filename of the img to be displayed
  Robot.drawBMP(buffer, 0, 0); // draw the file on the screen
  // change control modes
  switch (mode) {
    case CONTROL_MODE_COMPASS:
      compassControl(3);
      break;
    case CONTROL_MODE_KEY:
      keyboardControl();
      break;
  }
  delay(200);
}

void keyboardControl() {
  //Use buttons to control the gallery
  while (true) {
    int keyPressed = Robot.keyboardRead(); // read the button values
    switch (keyPressed) {
      case BUTTON_LEFT:  // display previous picture
        if (--i < 1) i = NUM_PICS;
        return;
      case BUTTON_MIDDLE:  // do nothing
      case BUTTON_RIGHT:  // display next picture
        if (++i > NUM_PICS) i = 1;
        return;
      case BUTTON_UP:  // change mode
        changeMode(-1);
        return;
      case BUTTON_DOWN:  // change mode
        changeMode(1);
        return;
    }
  }
}

// if controlling by the compass
void compassControl(int change) {
  // Rotate the robot to change the pictures
  while (true) {
    // read the value of the compass
    int oldV = Robot.compassRead();

    //get the change of angle
    int diff = Robot.compassRead() - oldV;
    if (diff > 180) diff -= 360;
    else if (diff < -180) diff += 360;

    if (abs(diff) > change) {
      if (++i > NUM_PICS) i = 1;
      return;
    }

    // chage modes, if buttons are pressed
    int keyPressed = Robot.keyboardRead();
    switch (keyPressed) {
      case BUTTON_UP:
        changeMode(-1);
        return;
      case BUTTON_DOWN:
        changeMode(1);
        return;
    }
    delay(10);
  }
}

// Change the control mode and display it on the LCD
void changeMode(int changeDir) {
  // alternate modes
  mode += changeDir;
  if (mode < 0) {
    mode = 1;
  } else if (mode > 1)
    mode = 0;

  // display  the mode on screen
  Robot.fill(255, 255, 255);
  Robot.stroke(255, 255, 255);
  Robot.rect(0, 0, 128, 12);
  Robot.stroke(0, 0, 0);
  Robot.text("Control:", 2, 2);
  Robot.text(modeNames[mode], 52, 2);
  delay(1000);
}