annotate examples/03-Analog/analog-output/render.cpp @ 507:1cec96845a23 prerelease

Explanted explantation

/*
 ____  _____ _        _    
| __ )| ____| |      / \   
|  _ \|  _| | |     / _ \  
| |_) | |___| |___ / ___ \ 
|____/|_____|_____/_/   \_\

The platform for ultra-low latency audio and sensor processing

http://bela.io

A project of the Augmented Instruments Laboratory within the
Centre for Digital Music at Queen Mary University of London.
http://www.eecs.qmul.ac.uk/~andrewm

(c) 2016 Augmented Instruments Laboratory: Andrew McPherson,
  Astrid Bin, Liam Donovan, Christian Heinrichs, Robert Jack,
  Giulio Moro, Laurel Pardue, Victor Zappi. All rights reserved.

The Bela software is distributed under the GNU Lesser General Public License
(LGPL 3.0), available here: https://www.gnu.org/licenses/lgpl-3.0.txt
*/


#include <Bela.h>
#include <rtdk.h>
#include <cmath>

// Set range for analog outputs designed for driving LEDs
const float kMinimumAmplitude = (1.5 / 5.0);
const float kAmplitudeRange = 1.0 - kMinimumAmplitude;

float gFrequency;
float gPhase;
float gInverseSampleRate;

bool setup(BelaContext *context, void *userData)
{
	// Retrieve a parameter passed in from the initAudio() call
	gFrequency = *(float *)userData;

	if(context->analogFrames == 0) {
		rt_printf("Error: this example needs the matrix enabled\n");
		return false;
	}

	gInverseSampleRate = 1.0 / context->analogSampleRate;
	gPhase = 0.0;

	return true;
}

void render(BelaContext *context, void *userData)
{
	for(unsigned int n = 0; n < context->analogFrames; n++) {
		// Set LED to different phase for each matrix channel
		float relativePhase = 0.0;
		for(unsigned int channel = 0; channel < context->analogChannels; channel++) {
			float out = kMinimumAmplitude + kAmplitudeRange * 0.5f * (1.0f + sinf(gPhase + relativePhase));

			analogWrite(context, n, channel, out);

			// Advance by pi/4 (1/8 of a full rotation) for each channel
			relativePhase += M_PI * 0.25;
		}

		gPhase += 2.0 * M_PI * gFrequency * gInverseSampleRate;
		if(gPhase > 2.0 * M_PI)
			gPhase -= 2.0 * M_PI;
	}
}

void cleanup(BelaContext *context, void *userData)
{

}


/**
\example analog-output/render.cpp

Fading LEDs
-----------

This sketch uses a sine wave to drive the brightness of a series of LEDs 
connected to the eight analog out pins. Again you can see the nested `for` loop 
structure but this time for the analog output channels rather than the audio.

- connect an LED in series with a 470ohm resistor between each of the analogOut pins and ground.

Within the first for loop in render we cycle through each frame in the analog 
output matrix. At each frame we then cycle through the analog output channels 
with another for loop and set the output voltage according to the phase of a 
sine tone that acts as an LFO. The analog output pins can provide a voltage of 
~4.092V.

The output on each pin is set with `analogWrite()` within the for loop that 
cycles through the analog output channels. This needs to be provided with 
arguments as follows `analogWrite(context, n, channel, out)`. Channel is 
where the you give the address of the analog output pin (in this case we cycle 
through each pin address in the for loop), out is the variable that holds the 
desired output (in this case set by the sine wave).

Notice that the phase of the brightness cycle for each led is different. This 
is achieved by updating a variable that stores a relative phase value. This 
variable is advanced by pi/4 (1/8 of a full rotation) for each channel giving 
each of the eight LEDs a different phase.
*/