I wrote this function over a year ago, just backing up all the trash on my external HDD

pwm_led_chaser.ino

inline void AnalogOutputTest(uint8_t startPin, uint8_t endPin, const int& timePerCycle, uint8_t incr = 5){
	///checks pwm pins
	if (startPin > endPin ) { // replace start & end pins
		int cpStart = startPin,
			cpEnd = endPin;
		startPin=cpEnd;endPin=cpStart;	
	} else if (startPin == endPin) {

		double delayTime = timePerCycle / ((startPin + 1 - endPin) * 51);

		//fade the led in and out once
		for (int fadeValue = 0; fadeValue <= 255; fadeValue += 5) { 
			analogWrite(startPin, fadeValue);
			delay(delayTime);
		}
		for (int fadeValue = 255; fadeValue >= 0; fadeValue -= 5) { 
			analogWrite(startPin, fadeValue);
			delay(delayTime);
		}

	} else {
	
		double delayTime = timePerCycle / ((endPin + 1 - startPin) * 51);
		
		// for each pin...
		for (int currentpin = startPin + 1; currentpin <= endPin; currentpin++)
			for (int fadeValue = 255; fadeValue >= 0; fadeValue -= 5) {//fade brightness

				analogWrite(currentpin, fadeValue);
				
				if (currentpin != endPin) 
					analogWrite(currentpin, 255 - fadeValue);

				delay(delayTime);
			}

	}
}


void setup(){
	//nothing to do here

} 

void loop(){

	AnalogOutputTest(2, 13, 1000);




/* replaces
	// for each pin...
	for (int currentpin = 2; currentpin != 13; currentpin++)
	
		for (int lysstryke = 255; lysstryke >= 0; lysstryke -= 5) {//fade brightness

			analogWrite(currentpin, lysstryke);

			if (currentpin == 13) // end of row (start next cycle)
				analogWrite(2, 255 - lysstryke);
			else 
				analogWrite(currentpin+1, 255-lysstryke);
			
			delay(10); // wait 10ms
		}
*/
}