Author: Florian Ledermann (ledermann@ims.tuwien.ac.at)

To get an overview, the graphical schema representation is the recommended entry point.

Links to

APRIL provides language elements for describing

  • The input and output devices of a system and its users (Low-level interaction)
  • Interaction modalities available to the user (high-level interaction)
  • Binding of abstract story concepts to concrete media objects.
  • Basic arrangement of media resources (models, sounds, images, ...) in time and space through animation.
  • Temporal and logical progression of the presentation (flow control)

 The root element of every APRIL file. Wrapper element for input and output device configuration. The config section of the APRIL file specified as src is imported (if present), and overlayed with the information of the local config section (this means that local elements with the same id as in the src file, and their child-elements, override the elements specified in the src file). The low-level tracking configuration is done in the OpenTracker file specified with the otsource attribute, or inline in the corresponding interaction elements (see below). If there is no setup element, APRIL looks for a file called "default.aps" in the presentations directory. Wrapper element for all devices connected to a single computer. Multiple hosts are NOT IMPLEMENTED. Configures a VGA output port. Screen resolution in pixels. Defines a display for rendering content on. The containing displaytracking and/or headtracking elements define optional tracking, this elements configures the position of the display window on an output port, its resolution and the default camera pose in the world. Configures the headtracking for the parent display element. Configures tracking of the center of the display. Configures a 2d-pointing device for the display, which can be used to interact with widgets or point on real/virtual things. Currently this is hard-coded to use the mouse input. ID to uniquely identify this display. The screen number this display window should be rendered on. position of the top left corner of the display window on the screen in pixels or percentage. Size of the display on screen in pixels or percentage. Flag indicating if frame-interleved stereo should be used. The position of the center of the image plane in world coordinates. Overridden if a displaytracking element is used. Size of the image plane in the world. Orientation of the image plane in the world. Overridden if a displaytracking element is used. Offest of the left eye for a stereo display. Offest of the right eye for stereo displays. The world position of the viewpoint. Overridden if a headtrtacking element is used. "AR" (default value) displays the actors of the presentation. "VR" also renders the stage elements for a virtual reality view onto the scene. If set to true, debug information is shown in the display. Defines a tracked artifact like a marker. NOT IMPLEMENTED. A hardware button that can be used for user input. URI of external file containing the config section to use. If a src is specified, any inline specifications will be ignored and the configuration specified in the given file will be used. We should support something like overlays, i.e. the config loaded from file is overlayed with the inline definitions! URI of OpenTracker config file to use as a basis for the tracking configuration. Named OpenTracker nodes referenced in the APRIL file are referenced from this file. Path to the executable(s) of the traget platform. This is the top-level wrapper element of a APRIL presentation. The content of this element specifies the logic (or the "story") of the presentation as a hierarchical state machine. The syntax is derived from XMI, the official UML-to-XML serialization syntax, but simplified for better readability. A unique name to identify this story. This element holds all references to used media resources (models, images, sounds, scripts etc.). Defines geometry as a proxy for real world objects. In augmented reality applications, this is not displayed, but used for correct rendering of intersections between virtual and real content, for example. In VR and authoring setups, these objects may be rendered as regular scene objects. Defines an actor of the presentation as an instance of a nAPRIL component. Inside the actor element, default values for its input fields can be set by using input elements. Defines the default value for a specific input for this presentation. Id ofthe field to set. Default value of that field. Unique id of the actor. Source of the component definition file. A light source, either real or virtual. NOT IMPLEMENTED. A sound to be played in the presentation. NOT IMPLEMENTED. The behaviours section binds behaviours of objects to states of the story logic. A behavior is a set of property changes bound to a state of the tory logic. Whenever the state is entered, the actions defined in the "entry" sub-element are performed. If the story is still in this state after perfomring the entry actions, the "do" actions are performed, and can be interrupted at any time by leaving the state. Upon leving the state, the "exit" actions are guaranteed to perform. The "entry" actions are performed when the associated state is entered. Actions defined here are guaranteed to perform, now matter how long the story remains in this state. Actions should therefore only be "set" and "connect", and very short "animate"ions. Allows explicit setting of the duration of the entry substate. If this is not used, the dration is calculated from the set and animate elements inside. Actions in this group are performed as long as the story is in the associated state. Note that actions might not be called at all, if the state is immediately left. This is the only place where looped animations make sense, because they can be cancelled by leaving the state. Actions defined here are executed when the associated state is left. They are guaranteed to perform. ID of the scene this behavior should be bound to. This triggers the associated transition automatically after a specified time. Time after which the transition should trigger. This disables a transition. Same as leaving it empty. This always triggers the transition immediately. This creates or uses a button when the transition becomes available, that can be pressed by the user to trigger the transition. Whether to create a virtual button. DEPRECATED. The label printed on the (virtual) button. This allows the user to use a raypicker to point at objects in the scene. If the specified actor or stage object is selected, the transition fires. ID of the actor or stage object that must be selected to trigger the transition. Evaluates an output of an actor against a fixed value or another output. If the expression evaluates to true, the transition fires. Actor or tracking element that should be used as input. Output field of the source to use. For tracking elements, position and orientation are available outputs. The kind of comparison to perform. One of equal (default), lessThan, greaterThan, lessOrEqual, greaterOrEqual, notEqual, isInside (bounding box check), notInside. The fixed value the source output should be compared to. A second actor or tracking element that delivers the output for comparison. The output of the second source to be used. ID of the transition this interaction is mapped to. Unique ID for this presentation. Depending on the implementation of the transformation of APRIL to a specific platform, this will be used for generating file- or folder names for the resulting files. The name of the presentation. This can be used by target platforms as a human-readable title for the presentation. A state in a hierarchical state machine. A transition from one state to another, specifying the transition event name. Name of the event to trigger the transition. Id of the source scene of the transition. Id of the target scene of the transition. A guard string, that can contian the id of another state. This means that the transition is only available if the story is currently in this state. Wrapper element to seperate multiple concurrent sub-engines inside a superstate. Inside this element, any annotation might be added to describe what is happening inside this scene. If set to true, the transition triggers automatically if it is the only available transition. NOT IMPLEMENTED Base type for stage, actor, light and sound elements. DEPRECATED. You can specify content inline by wrapping it with this tag and putting it as a first child of the actor element. Note that if a src attribute is present on the parent element, the inline content will be treated as if specified within an alt tag, i.e. only used when the content specified by src cannot be retrieved. You can specify content inline by wrapping it with this tag and putting it as a first child of the actor element. Note that if a src attribute is present on the parent element, the inline content will be treated as if specified within an alt tag, i.e. only used when the content specified by src cannot be retrieved. Unique id of this element. The MIME-type of the content. The URI to load the content from. Unique id of this element. Base type for set, animate, connect and control elements. Which input field of the actor to set. The target actor. Base type for entry, exit, do elements. For every actor, you can specify a sequence of set, animate and connect statements here. Sets the given input of a component instance to the given value. New value for the input. Time after enter/exit the change should happen. Animates the given input. For further information, see the SMIL animation spec. The start time of the animation, measured from the enter/exit time of the state. The duration of the animation. Target value of the input. Relative target value of the input. NOT IMPLEMENTED CalcMode like defined in the SMIL animation spec. NOT IMPLEMENTED, always linear at the moment. Connects an input of an actor to an output of another actor (master). The connection remains for the duration of the container state. Master actor to connect the field from. Which output of the master actor to use. Allows the user to control an input of an actor. If the id of a station is given, this station is used to control the input (via its position and orientation outputs), otherwise PUC is used to control the input. Lower limit of the value range that can be set. Upper limit of the value range that can be set. A label shown to the user together with the control for changing the input. ID of a station (defined in the setup element) to be used to contol the property. Station inputs can only be used to control inputs with types SFVec3f or SFRotation. Base type for trackable objects. Allows specification of an OT source either by reference or by inline OT code. ID to identify this element. DEF name of an OpenTracker node in the included OpenTracker file (or an earlier configured inline OT node) Base type for visible actors. DEPRECATED. Position of the object in world coordinates. Orientation of the object in the world. Scale factor for this object. Transparency value for this object. DEPRECTED, use components for all your actors. Transparency for real-world objects doesn't make much sense... DEPRECATED Base type for scenes. Name of the state. Marker attribute for initial states. list of double values, base type for restricted data types like vectors, rotations, etc. list of integer values, useful for list of indices. a simple type storing two float values, separated by spaces. a simple type storing three float values separated by spaces. a simple type storing four float values separated by spaces. a simple type storing two integer values separated by spaces. either two numbers, indicating absolute pixels, or two percentage values, or the keyword "fullscreen".