Scenic.ViewPort (Scenic v0.10.3) View Source
Overview
The job of the ViewPort
is to coordinate the flow of information between
the scenes and the drivers. Scenes and Drivers should not know anything
about each other. An app should work identically from its point of view
no matter if there is one, multiple, or no drivers currently running.
Drivers are all about rendering output and collecting input from a single source. Usually hardware, but can also be the network or files. Drivers only care about graphs and should not need to know anything about the logic or state encapsulated in Scenes.
The goal is to isolate app data and logic from render data and logic. The ViewPort is the connection between them that makes sense of the flow of information.
OUTPUT
Practically speaking, the ViewPort
is the owner of the ETS tables that
carry the graphs (and any other necessary support info). If the ViewPort
crashes, then all that information needs to be rebuilt. The ViewPort monitors
all running scenes and does the appropriate cleanup when any of them
goes DOWN.
The scene is responsible for generating graphs and writing them to the graph ETS table. (Note: We also tried casting the graph to the ViewPort so that the table could be non-public, but that had issues)
The drivers should only read from the graph tables.
INPUT
When user input happens, the drivers send it to the ViewPort
.
Input that does not depend on screen position (key presses, audio
window events, etc.) is sent to the root scene unless some other
scene has captured that type of input (see captured input below).
If the input event does depend on position (cursor position, cursor button presses, scrolling, etc.) then the ViewPort needs to scan the hierarchical graph of graphs, to find the correct scene, and the item in that scene that was "hit". The ViewPort then sends the event to that scene, with the position projected into the scene's local coordinate space (via the built-up stack of matrix transformations)
CAPTURED INPUT
A scene can request to "capture" all input events of a certain type. This means that all events of that type are sent to a certain scene process regardless of position or root. In this way, a text input scene nested deep in the tree can capture key presses. Or a button can capture cursor_pos events after it has been pressed.
If a scene has "captured" a position dependent input type, that position is projected into the scene's coordinate space before sending the event. Note that instead of walking the graph of graphs, the transforms provided in the input "context" field are used. You could, in theory change that to something else before capturing, but I wouldn't really recommend it.
Any scene can cancel the current capture. This would probably leave the scene that thinks it has "captured" the input in an inconsistent state, so this is not recommended.
Link to this section Summary
Functions
Capture one or more types of input.
Cast a message to all active drivers listening to a viewport.
query the last recorded viewport status
Send raw input to a viewport.
release an input capture.
Request that a {:set_root, ...}
message is sent to the caller.
Reset a running viewport
Set the root scene/graph of the ViewPort.
Start a new viewport
Stop a running viewport
Link to this section Types
Specs
Link to this section Functions
Specs
capture_input( context :: Scenic.ViewPort.Context.t(), input_class :: Scenic.ViewPort.Input.class() | [Scenic.ViewPort.Input.class()] ) :: :ok
Capture one or more types of input.
This must be called by a Scene process.
Cast a message to all active drivers listening to a viewport.
Specs
info(viewport :: GenServer.server()) :: {:ok, Scenic.ViewPort.Status.t()}
query the last recorded viewport status
Specs
input(viewport :: GenServer.server(), input :: Scenic.ViewPort.Input.t()) :: :ok
Send raw input to a viewport.
This is used primarily by drivers to send raw user input to the viewport. Having said that, nothing stops a scene from using it to send input into the system. There are a few cases where that is useful.
See the input docs for the input formats you can send.
Specs
input( viewport :: GenServer.server(), input :: Scenic.ViewPort.Input.t(), context :: Scenic.ViewPort.Context.t() ) :: :ok
release an input capture.
This is intended be called by a Scene process, but doesn't need to be.
Specs
request_root( viewport :: GenServer.server(), send_to :: nil | GenServer.server() ) :: :ok
Request that a {:set_root, ...}
message is sent to the caller.
request_root
is primarily used by drivers and is of little use to anything
else.
When a driver starts up, it will need to get the root scene of the viewport,
which may already be up and running. By calling request_root
, the driver
can request that the viewport send it a {:set_root, ...}
message as if
the root scene had just changed.
Params:
viewport
The viewport to request the message from.send_to
The driver to send the message to. Ifsend_to
is nil, the message will be sent to the calling process.
Specs
reset(viewport :: GenServer.server()) :: :ok
Reset a running viewport
This causes the viewport to rest the original scene as the root, with the original arguments were received with the ViewPort started.
Specs
reshape(viewport :: GenServer.server(), size :: Scenic.Math.point()) :: :ok
Specs
set_root( viewport :: GenServer.server(), scene :: atom() | {atom(), any()}, args :: any() ) :: :ok
Set the root scene/graph of the ViewPort.
Specs
Start a new viewport
Specs
stop(viewport :: GenServer.server()) :: :ok
Stop a running viewport