Note: this tutorial will introduce the original bindings for MaxMSP (before July 2013). You can access the tutorial for the revised multi-object bindings here.
To start using the libmapper with MaxMSP you will need to:
[mapper]
external object from our downloads page.
Alternatively, you can build the object from
source instead.To create a libmapper device, it is necessary to provide a device
name to the [mapper]
object using the property @alias
.
There is an initialization period after a device is created where
a unique ordinal is chosen to append to the device name.
This allows multiple devices with the same name to
exist on the network. If no name is given libmapper will choose a
name for your device starting with the string "maxmsp".
If desired, a device definition file can be specified with the property
@definition
or @def
, which the external will use to add signals
to your device. Otherwise, you device will start with no inputs
or outputs and you will need to add them using messages. In this tutorial,
we will assume that you do not have a prepared device definition file.
A third optional parameter of the [mapper]
object is a network
interface name. By default, libmapper will try to guess which network
interface to use for mapping, defaulting to the local loopback interface if
ethernet or wifi is not available. You can force the object to use a
particular interface by using the @interface
property.
An example of creating a device:
Once the object has initialized, it will output its metadata from the right outlet:
Now that we have created a device, we only need to know how to
add signals in order to give our program some input/output functionality.
While libmapper enables arbitrary connections between any declared signals,
we still find it helpful to distinguish between two type of signals: inputs
and outputs
.
outputs
signals are sources of data, updated locally by their parent deviceinputs
signals are consumers of data and are not generally
updated locally by their parent device.This can become a bit confusing, since the "reverb" parameter of a sound
synthesizer might be updated locally through user interaction with a GUI,
however the normal use of this signal is as a destination for control data
streams so it should be defined as an input
signal. Note that this distinction
is to help with GUI organization and user-understanding – libmapper
enables connections from input signals and to output signals if desired.
We'll start with creating a "sender", so we will first talk about how to update output signals. Creating a signal requires two pieces of information:
integer
, 'f'
for float
Additional signal properties can also (optionally) be added:
examples:
The only required parameters here are the signal name,
and data type. If no length
property is provided, the signal is
assumed to have length 1.
Finally, supported types are currently 'i' or 'f' for int
or
float
values, respectively.
The other parameters are not strictly required, but the more
information you provide, the more the mapper can do some things
automatically. For example, if minimum
and maximum
are provided,
it will be possible to create linear-scaled connections very quickly.
If unit
is provided, the mapper will be able to similarly figure out
a linear scaling based on unit conversion (centimeters to inches for
example). Currently automatic unit-based scaling is not a supported
feature, but will be added in the future. You can take advantage of
this future development by simply providing unit information whenever
it is available. It is also helpful documentation for users.
An example of creating a "barebones" int
scalar output signal with
no unit, minimum, or maximum information:
An example of a float
signal where some more information is provided:
So far we know how to create a device and to specify an output signal for it.
We can imagine the above program getting sensor information in a loop. It could be running on a computer and reading data from an Arduino over a USB serial port, or it could just be a mouse-controlled GUI slider. However it's getting the data, it must provide it to libmapper so that it will be sent to other devices if that signal is mapped.
This is accomplished by passing messages to the [mapper]
object
starting with the signal name:
(<signal_name> <value>)
|
So in the "sensor 1 voltage" example, assuming that we have some code
which reads sensor 1's value into a float variable in [p read_sensor]
,
the patch becomes:
This is about all that is needed to expose sensor 1's voltage to the network as a mappable parameter. The libmapper GUI can now be used to create a mapping between this value and a receiver, where it could control a synthesizer parameter or change the brightness of an LED, or whatever else you want to do.
Most synthesizers of course will not know what to do with "voltage"--it is an electrical property that has nothing to do with sound or music. This is where libmapper really becomes useful.
Scaling or other signal conditioning can be taken care of before exposing the signal, or it can be performed as part of the mapping. Since the end user can demand any mathematical operation be performed on the signal, he can perform whatever mappings between signals as he wishes.
As a developer, it is therefore your job to provide information that will be useful to the end user.
For example, if sensor 1 is a position sensor, instead of publishing "voltage", you could convert it to centimeters or meters based on the known dimensions of the sensor, and publish a "/sensor1/position" signal instead, providing the unit information as well.
We call such signals "semantic", because they provide information with more meaning than a relatively uninformative value based on the electrical properties of the sensing technique. Some sensors can benefit from low-pass filtering or other measures to reduce noise. Some sensor data may need to be combined in order to derive physical meaning. What you choose to expose as outputs of your device is entirely application-dependent.
You can even publish both "/sensor1/position" and "/sensor1/voltage" if desired, in order to expose both processed and raw data. Keep in mind that these will not take up significant processing time, and zero network bandwidth, if they are not mapped.
Receiving signals is even easier: after adding an input using the add input
message, updates for this signal will be routed to the left output
of the [mapper]
object. Let's try making two devices in the same patch
for testing.
If you use your mapping GUI to create a map between your two signals sendsig and recvsig, any change made to the float value on the left will cause a corresponding output on the right.
Congratulations - you have created your first mapping connection! This probably seems quite simplistic, since you could have made a patch-cord between the two float objects and accomplished the same thing, but your "mapping" represents something more:
For patches with only outputs, lazy users can also declare the signals
automatically using learn
mode. You can either send the message
"learn 1" to turn on learning ("learn 0" to turn it off) or you can
instantiate your [mapper]
object with the learn property set as an
argument:
the object will watch its inlet for messages formatted as /<name> value(s)
and add any unknown signals automatically. Signals added this way will not
have associated minimum or maximum values, however, so it is usually
recommended to add the signals explicitly using messages.
If you wish, you can declare your libmapper signals using a device definition
file instead of sending messages to the [mapper]
object. This file should be
correctly-formatted JSON with the following structure:
{
"device" : {
"fileversion" : "dot-1",
"name" : "tester",
"inputs" : [
{
"name" : "/in1",
"type" : "f"
}
],
"outputs" : [
{
"name" : "/out1",
"type" : "f",
"units" : "cm",
"minimum" : 4.0,
"maximum" : 5.1
}
]
}
}
To load your device definition, simply instantiate your [mapper]
object with
the file name as a property:
Things like device names, signal units, and ranges, are examples of metadata--information about the data you are exposing on the network.
libmapper also provides the ability to specify arbitrary extra metadata in the form of name-value pairs. These are not interpreted by libmapper in any way, but can be retrieved over the network. This can be used for instance to label a device with its location, or to perhaps give a signal some property like "reliability", or some category like "light", "motor", "shaker", etc.
Some GUI could then use this information to display information about the network in an intelligent manner.
Any time there may be extra knowledge about a signal or device, it is a good idea to represent it by adding such properties, which can be of any OSC-compatible type. (So, numbers and strings, etc.)
The MaxMSP bindings for libmapper do not currently allow dynamically changing the properties of a device or signal, however they can be declared when the entity is created by using jitter-style property arguments
For example, to store a float
indicating the X position of a device
dev
, you could instantiate your object like this:
To specify a string property of a signal:
You can use any property name not already reserved by libmapper.
Object | Reserved keys |
---|---|
All | data , description , id , is_local , name , status , version |
Device | host , libversion , num_maps , num_maps_in , num_maps_out , num_sigs_in , num_sigs_out , ordinal , port , signal , synced |
Signal | device , direction , ephemeral , jitter , length , max , maximum , min , minimum , num_inst , num_maps , num_maps_in , num_maps_out , period , rate , steal , type , unit |
Maps | bundle , expr , muted , num_destinations , num_sources , process_loc , protocol , scope , signal , slot , use_inst |