int inputPinRed = 2;
int inputPinGreen = 3;
int inputPinBlue = 4;

int outputPinRed = 9;
int outputPinGreen = 10;
int outputPinBlue = 11;

int dutyCycleRed = 0;
int dutyCycleGreen = 0;
int dutyCycleBlue = 0;

int upDutyCycleRed = 0;
int upDutyCycleGreen = 0;
int upDutyCycleBlue = 0;

int buttonPressedRed = 0;
int buttonPressedGreen = 0;
int buttonPressedBlue = 0;

void setup()
{
    Serial.begin(9600);

    pinMode(inputPinRed, INPUT);
    pinMode(inputPinGreen, INPUT);
    pinMode(inputPinBlue, INPUT);

    pinMode(outputPinRed, OUTPUT);
    pinMode(outputPinGreen, OUTPUT);
    pinMode(outputPinBlue, OUTPUT);
}

void loop()
{
    checkButtons();
    changeDutyCycles();
    delay(200);
}

void checkButtons()
{
    checkButton(&buttonPressedRed, &inputPinRed, &upDutyCycleRed);
    checkButton(&buttonPressedBlue, &inputPinBlue, &upDutyCycleBlue);
    checkButton(&buttonPressedGreen, &inputPinGreen, &upDutyCycleGreen);
}

void checkButton(int* buttonPressed, int* inputPin, int* upDutyCycle)
{
    int buttonPressedBefore = *buttonPressed;
    *buttonPressed = digitalRead(*inputPin) == LOW;
    if(!buttonPressedBefore && *buttonPressed)
        *upDutyCycle = !*upDutyCycle;
}

void changeDutyCycles()
{
    if (buttonPressedRed) changeDutyCycle(&dutyCycleRed, &upDutyCycleRed, &outputPinRed);
    if (buttonPressedBlue) changeDutyCycle(&dutyCycleBlue, &upDutyCycleBlue, &outputPinBlue);
    if (buttonPressedGreen) changeDutyCycle(&dutyCycleGreen, &upDutyCycleGreen, &outputPinGreen);
}

void changeDutyCycle(int* dutyCycle, int* upDutyCycle, int* outputPin)
{
    *dutyCycle += *upDutyCycle ? 4 : -4;
    if (*dutyCycle > 255) *dutyCycle = 255;
    if (*dutyCycle < 0) *dutyCycle = 0;
    analogWrite(*outputPin, *dutyCycle);
}