render.cpp

/*
 ____  _____ _        _
| __ )| ____| |      / \
|  _ \|  _| | |     / _ \
| |_) | |___| |___ / ___ \
|____/|_____|_____/_/   \_\
http://bela.io
*/
/**
\example Analog/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 channels. 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 `analogWriteOnce()` within the for loop that
cycles through the analog output channels. This needs to be provided with
arguments as follows `analogWriteOnce(context, n, channel, out)`. Channel is
where 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) and `n` is the frame number
(given by the other for loop).

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.
*/

#include <Bela.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 = 3.0;
float gPhase;
float gInverseSampleRate;

bool setup(BelaContext *context, void *userData)
{

	// Check if analog channels are enabled
	if(context->analogFrames == 0 || context->analogFrames > context->audioFrames) {
		rt_printf("Error: this example needs analog enabled, with 4 or 8 channels\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 analog output channel
		float relativePhase = 0.0;
		for(unsigned int channel = 0; channel < context->analogOutChannels; channel++) {
			float out = kMinimumAmplitude + kAmplitudeRange * 0.5f * (1.0f + sinf(gPhase + relativePhase));

			analogWriteOnce(context, n, channel, out);

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

		// Update and wrap phase of sine tone
		gPhase += 2.0f * (float)M_PI * gFrequency * gInverseSampleRate;
		if(gPhase > M_PI)
			gPhase -= 2.0f * (float)M_PI;
	}
}

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

}