55 ClutterScript

Loads a scene from UI definition data

55.1 Overview

<clutter-script> is an object used for loading and building parts or a complete scenegraph from external definition data in forms of string buffers or files.

The UI definition format is JSON, the JavaScript Object Notation as described by RFC 4627. <clutter-script> can load a JSON data stream, parse it and build all the objects defined into it. Each object must have an "id" and a "type" properties defining the name to be used to retrieve it from <clutter-script> with clutter-script-get-object, and the class type to be instanciated. Every other attribute will be mapped to the class properties.

A <clutter-script> holds a reference on every object it creates from the definition data, except for the stage. Every non-actor object will be finalized when the <clutter-script> instance holding it will be finalized, so they need to be referenced using g-object-ref in order for them to survive.

A simple object might be defined as:

     
     {
       "id"     : "red-button",
       "type"   : "ClutterRectangle",
       "width"  : 100,
       "height" : 100,
       "color"  : "#ff0000ff"
     }

This will produce a red <clutter-rectangle>, 100x100 pixels wide, and with a ClutterScript id of "red-button"; it can be retrieved by calling:

     
     ClutterActor *red_button;
     
     red_button = CLUTTER_ACTOR (clutter_script_get_object (script, "red-button"));

and then manipulated with the Clutter API. For every object created using ClutterScript it is possible to check the id by calling clutter-get-script-id.

Packing can be represented using the "children" member, and passing an array of objects or ids of objects already defined (but not packed: the packing rules of Clutter still apply, and an actor cannot be packed in multiple containers without unparenting it in between).

Behaviours and timelines can also be defined inside a UI definition buffer:

     
     {
       "id"          : "rotate-behaviour",
       "type"        : "ClutterBehaviourRotate",
       "angle-start" : 0.0,
       "angle-end"   : 360.0,
       "axis"        : "z-axis",
       "alpha"       : {
         "timeline" : { "duration" : 4000, "loop" : true },
         "mode"     : "easeInSine"
       }
     }

And then to apply a defined behaviour to an actor defined inside the definition of an actor, the "behaviour" member can be used:

     
     {
       "id" : "my-rotating-actor",
       "type" : "ClutterTexture",
       ...
       "behaviours" : [ "rotate-behaviour" ]
     }

A <clutter-alpha> belonging to a <clutter-behaviour> can only be defined implicitly like in the example above, or explicitly by setting the "alpha" property to point to a previously defined <clutter-alpha>, e.g.:

     
     {
       "id"          : "rotate-behaviour",
       "type"        : "ClutterBehaviourRotate",
       "angle-start" : 0.0,
       "angle-end"   : 360.0,
       "axis"        : "z-axis",
       "alpha"       : {
         "id"       : "rotate-alpha",
         "type"     : "ClutterAlpha",
         "timeline" : {
           "id"       : "rotate-timeline",
           "type      : "ClutterTimeline",
           "duration" : 4000,
           "loop"     : true
         },
         "function" : "custom_sine_alpha"
       }
     }

Implicitely defined <clutter-alpha>s and <clutter-timeline>s can omit the well as the clutter-script-get-object (they can, however, be extracted using the <clutter-behaviour> and <clutter-alpha> API respectively).

Signal handlers can be defined inside a Clutter UI definition file and then autoconnected to their respective signals using the clutter-script-connect-signals function:

     
       ...
       "signals" : [
         { "name" : "button-press-event", "handler" : "on_button_press" },
         {
           "name" : "foo-signal",
           "handler" : "after_foo",
           "after" : true
         },
       ],
       ...

Signal handler definitions must have a "name" and a "handler" members; they can also have the "after" and "swapped" boolean members (for the signal connection flags ‘G_CONNECT_AFTER’ and ‘G_CONNECT_SWAPPED’ respectively) and the "object" string member for calling g-signal-connect-object instead of g-signal-connect.

Signals can also be directly attached to a specific state defined inside a <clutter-state> instance, for instance:

     
       ...
       "signals" : [
         {
           "name" : "enter-event",
           "states" : "button-states",
           "target-state" : "hover"
         },
         {
           "name" : "leave-event",
           "states" : "button-states",
           "target-state" : "base"
         },
         {
           "name" : "button-press-event",
           "states" : "button-states",
           "target-state" : "active",
         },
         {
           "name" : "key-press-event",
           "states" : "button-states",
           "target-state" : "key-focus",
           "warp" : true
         }
       ],
       ...

The "states" key defines the <clutter-state> instance to be used to resolve the "target-state" key; it can be either a script id for a <clutter-state> built by the same <clutter-script> instance, or to a <clutter-state> built in code and associated to the <clutter-script> instance through the clutter-script-add-states function. If no "states" key is present, then the default <clutter-state> associated to the <clutter-script> instance will be used; the default <clutter-state> can be set using clutter-script-add-states using a ‘#f’ name. The "warp" key can be used to warp to a specific state instead of animating to it. State changes on signal emission will not affect the signal emission chain.

Clutter reserves the following names, so classes defining properties through the usual GObject registration process should avoid using these names to avoid collisions:

     
       "id"         := the unique name of a ClutterScript object
       "type"       := the class literal name, also used to infer the type
                       function
       "type_func"  := the GType function name, for non-standard classes
       "children"   := an array of names or objects to add as children
       "behaviours" := an array of names or objects to apply to an actor
       "signals"    := an array of signal definitions to connect to an object
       "is-default" := a boolean flag used when defining the #ClutterStage;
                       if set to "true" the default stage will be used instead
                       of creating a new #ClutterStage instance

<clutter-script> is available since Clutter 0.6

55.2 Usage