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" : ... }
    ]
}
```