Display Coordinator Connector

The BUILD.gn in this directory generates a component package named display-coordinator-connector

It publishes the fuchsia.hardware.display.Provider service used for production environments which contents are displayed on the display hardware.

Introduction

The goal of display-coordinator-connector is to let components connect to the fuchsia.hardware.display.Coordinator service, provided by the display coordinator driver (available in /dev/class/display-coordinator) so that components can present contents to the display hardware.

It serves as a bridge to allow components to access the Coordinator service without having direct access to the /dev/class/display-coordinator directory.

display-coordinator-connector only supports a single client connection at any given time. Consequently, two instances of Scenic (or any other display clients) cannot be run simultaneously.

An extra hop between the display client and the display coordinator occurs when display-coordinator-connector is used to access the Coordinator service. However, the time overhead is negligible and is constant (in the number of display open requests) for most of the display clients (like Scenic).

Usage

Realms should declare a child component in its component manifest for the display coordinator connector. The child must be named display-coordinator-connector to make its capabilities be correctly routed.

They should also include the corresponding shard component manifest file display_coordinator_connector.shard.cml to route required capabilities to the display-coordinator-connector child.

They should also explicitly offer the fuchsia.hardware.display.Provider service from display-coordinator-connector to clients (for example, Scenic).

For example, here is an excerpt of the ui component manifest defined in //src/ui/meta/ui.cml declaring a real display coordinator connector from the global package URL, offering parent capabilities to the display coordinator connector, and providing the fuchsia.hardware.display.Provider service to Scenic:

{
  include: [
    "//src/graphics/display/bin/coordinator-connector/meta/display_coordinator_connector.shard.cml",
  ],
  children: [
    {
      name: "display-coordinator-connector",
      url: "fuchsia-pkg://fuchsia.com/display-coordinator-provider#meta/hdcp.cm",
    },
  ],
  offer: [
    {
      protocol: ["fuchsia.hardware.display.Provider"],
      from: "#display-coordinator-connector",
      to: ["#scenic"],
    },
  ],
}