Controlling the Grid with libmonome and C

Introduction

This guide aims to show how someone can use libmonome to control the grid from C.

Why do this? The big advantage that libmonome provides is that it doesn't require serialosc or OSC at all. The OSC communications layer, usually built on top of the UDP networking protocol, introduces a non-trivial amount of overhead. Using libmonome to directly control the grid will will make the grid consistently more responsive, and also much easier to debug.

The assumption here is that readers are already familiar with the C programming language and building programs from the commandline. The presented code has been tested to work on both Linux and OSX.

Writing a program using the Grid can boiled down to three things: A. handling button presses (down and up), B. controlling the LED lights (on and off), and C. making other things happen while managing the grid (making sound, video, etc). This guide/tutorial will address (A) and (B) directly, while paving the way for (C).

Hello Grid

To begin, here's very simple "hello grid" program:

<<00_hello.c>>=

#include <stdlib.h>
#include <monome.h>
#include <stdio.h>
#include <signal.h>
#include <unistd.h>

unsigned int grid[16][16];

void handle_press(const monome_event_t *e, void *data) {
    unsigned int x, y;

    x = e->grid.x;
    y = e->grid.y;

    /* toggle the button */
    grid[x][y] = !grid[x][y];
    monome_led_set(e->monome, x, y, grid[x][y]);
}

int main(int argc, char *argv[]) {
    monome_t *monome;

    if (argc < 2) {
        printf("Usage %s device_path\n", argv[0]);
        return 1;
    }

    int x, y;

    for(x = 0; x < 16; x++)
        for(y = 0; y < 16; y++) grid[x][y] = 0;

    if( !(monome = monome_open(argv[1], "8000")) )
        return -1;

    monome_led_all(monome, 0);

    monome_register_handler(monome, MONOME_BUTTON_DOWN, handle_press, NULL);

    monome_event_loop(monome);

    monome_close(monome);
    return 0;
}

The monome interface manages state in a struct called monome_t.

monome_open opens the monome device. Automatically will use OSC or serial directly based on filename. (This is important!)

monome_led_all will efficiently toggle all LEDs to be in and on or off state. It's being used to turn everything off (far more useful than turning everything on).

monome_register_handler will register a callback to the event loop. In this case, it's the MONOME_BUTTON_DOWNcallback, which is the function created called handle_press. This will get called every time a button is pushed.

monome_event_loop begins the event loop and starts listening to events.

monome_close will cleanly close the monome listener. However, in this current setup, it will never get here. More on that later.

monome_led_set is used to light a single led at a particular XY coordinate.

Breaking out the event loop

A more practical version of the previous example is shown below. Here, a signal interrupt is added so that it is possible to break out of the loop and cleanly exit with `monomeevent_loop` is replaced with a small while loop, with a small delay added so as to not eat up CPU cycles.

The new monome function here is used, monome_event_handle_next, which is what monome_event_loop was calling to process events.

Not only is this approach allow for a more graceful exit, but it also a more practical way to use it in larger pieces of software.

<<01_eventloop.c>>=

#include <stdlib.h>
#include <monome.h>
#include <stdio.h>
#include <signal.h>
#include <unistd.h>

unsigned int grid[16][16];

static volatile int is_running = 1;

void handle_press(const monome_event_t *e, void *data) {
    unsigned int x, y;

    x = e->grid.x;
    y = e->grid.y;

    /* toggle the button */
    grid[x][y] = !grid[x][y];
    monome_led_set(e->monome, x, y, grid[x][y]);
}

static void please_close(int sig)
{
    is_running = 0;
}

int main(int argc, char *argv[]) {
    monome_t *monome;
    int x, y;

    if (argc < 2) {
        printf("Usage %s device_path\n", argv[0]);
        return 1;
    }

    signal(SIGINT, please_close);

    for(x = 0; x < 16; x++)
        for(y = 0; y < 16; y++) grid[x][y] = 0;

    if( !(monome = monome_open(argv[1], "8000")) )
        return -1;

    monome_led_all(monome, 0);

    monome_register_handler(monome, MONOME_BUTTON_DOWN, handle_press, NULL);

    while(is_running) {
        while(monome_event_handle_next(monome));
        usleep(800);
    }

    printf("Closing!\n");
    monome_led_all(monome, 0);
    monome_close(monome);
    return 0;
}

More Efficient Drawing

As monome applications get more complex, independently setting LEDs with `monomeset` becomes noticeably slow. A more efficient route would involve setting LEDs one row at a time monome_led_row (8 calls on a regular Grid) or one quad at a time using monome_led_map (2 calls on a regular Grid).

This toggle LED example will be reworked to use quads with monome_led_map, as it is the most efficient way to draw a bunch of LEDs.

<<02_more_efficient.c>>=

#include <stdlib.h>
#include <monome.h>
#include <stdio.h>
#include <signal.h>
#include <unistd.h>
#include <stdint.h>

uint16_t grid[8];
static int please_draw = 0;

static uint8_t quadL[8];
static uint8_t quadR[8];

static volatile int is_running = 1;

void handle_press(const monome_event_t *e, void *data) {
    unsigned int x, y;
    int s;
    uint8_t *q;

    x = e->grid.x;
    y = e->grid.y;

    if (x >= 8) {
        q = quadR;
        x -= 8;
    } else {
        q = quadL;
    }

    s = (q[y] & (1 << x)) ? 0 : 1;

    if (s) {
        q[y] |= 1 << x;
    } else {
        q[y] &= ~(1 << x);
    }

    please_draw = 1;
}

static void redraw(monome_t *m, uint16_t *g)
{
    if (please_draw) {
        please_draw = 0;
        monome_led_map(m, 0, 0, quadL);
        monome_led_map(m, 255, 0, quadR);
    }
}

static void please_close(int sig)
{
    is_running = 0;
}

int main(int argc, char *argv[]) {
    monome_t *monome;

    int y;

    if (argc < 2) {
        printf("Usage %s device_path\n", argv[0]);
        return 1;
    }

    signal(SIGINT, please_close);

    for (y = 0; y < 8; y++) {
        quadL[y] = 0;
        quadR[y] = 0;
    }

    if( !(monome = monome_open(argv[1], "8000")) )
        return -1;

    monome_led_all(monome, 0);

    monome_register_handler(monome, MONOME_BUTTON_DOWN, handle_press, NULL);

    while(is_running) {
        while(monome_event_handle_next(monome));
        redraw(monome, grid);
        usleep(800);
    }

    printf("Closing!\n");

    monome_led_all(monome, 0);
    monome_close(monome);
    return 0;
}

A more interesting example

Using monome_led_map to redraw the entire screen every time a single LED button is toggled feels a bit overkill. This drawing approach really shines when many parts of the grid need to be redrawn, quickly.

So, our simple toggle app will be modified a bit to add some flair: every time a part of the grid is toggled, it will produce a virtual ripple.

To accomplish this, LEDs on the grid will be treated more like pixels on a very low resolution framebuffer. State will be maintained for the toggled states and ripple animations separately, and then drawn on the Grid at the last minute.

In addition, a few other structs and abstractions have been made. In particular, all program data that was once global data has now been consolidated into one struct created inside of the main function using malloc. This is a better practice. Not only does it make programs easier to manage this way, but removing global variables also eases off dependency on stack memory allocation, which is finite and can be very small on some systems.

<<03_ripples.c>>=