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TUHI

Tuhi is a DBus session daemon that connects to and fetches the data from the Wacom ink range (Spark, Slate, Folio, Intuos Paper, ...). The data is provided to clients in the form of JSON, any conversion to other formats like SVG must be done by the clients.

Tuhi is the Maori word for "to draw".

Supported Devices

Devices tested and known to be supported:

Bamboo Spark
Bamboo Slate

Units used by this interface

Physical distances for x/y axes are in µm from the sensor's top-right position.
Stylus pressure is normalized to a range of [0, 0xffff], inclusive.
Timestamps are in seconds in unix epoch, time offsets are in ms after the most recent timestamp.

DBus Interface

The following interfaces are provided:

org.freedesktop.tuhi1.Manager

Property: Devices (ao)

Array of object paths to known (previously paired, but not necessarily connected) devices.

org.freedesktop.tuhi1.Device

Interface to a device known by tuhi. Each object in Manager.Devices implements this interface.

Property: Name (s) Human-readable name of the device. Read-only

Property: Address (s) Bluetooth address of the device. Read-only

Property: Dimensions (uu) The physical dimensions (width, height) in µm Read-only

Property: DrawingsAvailable (u) An integer indicating the number of drawings available. Drawings are zero-indexed, see GetJSONData(). Read-only

Property: Listening (b) Indicates whether the daemon is currently listening for the device.

  This property is set to True when a Listen() request initiates the
  search for device connections. When the Listen() request completes
  upon timeout, the property is set to False.
  Read-only

Method: Listen() -> () Listen for data from this device. This method starts listening for events on the device for an unspecified timeout. When the timeout expires, a ListenComplete signal is sent indicating success or error.

  This function requires the device to be connected and may require some
  interactivity (e.g. the user may need to press the sync button).

  When the device connects, the daemon downloads all drawings from the
  device. If successfull, the drawings are deleted from the device. The
  data is held by the daemon in non-persistent storage until the daemon
  is stopped or we run out of memory, whichever happens earlier.  Use
  GetJSONData() to retrieve the data from the daemon.

  When drawings become available from the device, the DrawingsAvailable
  property updates to the number of available drawings.

  When this function is called multiple times, any new data is appended
  to the existing list of drawings. Calling Listen() before a previous
  call has completed is silently ignored and does not reset the timeout.

  Returns: 0 on success or a negative errno on failure

Method: GetJSONData(index: u) -> (s) Returns a JSON file with the drawings specified by the index argument. Drawings are zero-indexed and the requested index must be less than the DrawingsAvailable property value. See section JSON FILE FORMAT for the format of the returned data.

  Returns a string representing the JSON data from the last drawings or
  the empty string if no data is available or the index is invalid.

JSON File Format

Below is the example file format (with comments, not present in the real files). The JSON objects are "drawing" (the root object), "strokes", "points". Pseudo-code is used to illustrate the objects in the file.

class Drawing { version: uint32 devicename: string dimensions: [uint32, uint32] // x/y physical dimensions in µm timestamp: uint64 strokes: [ Stroke, Stroke, ...] }

The strokes list contains all strokes of a single drawing, each stroke consisting of a number of points.

class Stroke { points: [Point, Point, ...] }

The points list contains the actual pen data.

class Point { toffset: uint32 position: [uint32, uint32] pressure: uint32 }

An expanded file looks like this:

{
   "version" : 1,                       // JSON file format version number
   "devicename":  "Wacom Bamboo Spark", 
   "dimensions": [ 100000, 200000],      // width/height in µm
   "timestamp" : 12345,
   "strokes" : [
        {
            "points":  [
               // all items in a point are optional. Unknown dictionary
               // entries must be ignored as future devices may add
               // new axes.
               { "toffset" : 12366, "position" : [ 100, 200 ], "pressure" : 1000 },
               { "toffset" : 12368, "pressure" : 800 },
               { "toffset" : 12366, "position" : [ 120, 202 ] },
             ]
        },
        {  "points" : ... }
    ]
}