cobalt/site/docs/overview.md

Project: /youtube/cobalt/_project.yaml
Book: /youtube/cobalt/_book.yaml

# Getting started

Cobalt is a lightweight HTML5/CSS/JS application container that is designed
to provide a rich application development environment with minimal resource
consumption (deployment size, RAM, CPU, GPU). At the same time, Cobalt enables
a rich, low-latency user experience across a wide variety of platforms and
devices.

#### Target audiences

Cobalt's documentation is written with two audiences in mind:

*   **Porters** enable Cobalt to work on other platforms by using Starboard,
    Cobalt's porting layer and OS abstraction, to implement the
    platform-specific functionality that Cobalt uses. Each Starboard module
    (memory, socket, thread, etc.) defines functions that must be implemented
    for the porter's platform.

*   **Developers** want to build applications in familiar environments with
    advanced debugging tools without having to worry about compatibility with
    a highly fragmented set of browsers. At the same time, they want to have
    full control over their codebase so that they can ship features for
    constrained platforms, like TVs, on time and without technical risk.

## Benefits of Cobalt

Cobalt significantly reduces the cost of supporting a browser on non-standard
and resource-constrained platforms. In addition, since Cobalt operates at a
consolidated, versioned platform abstraction layer, its porting effort is
man-weeks, and subsequent rebases are near-free.

These are some other benefits that Cobalt provides:

*   **More platforms**

    *   Cobalt does not require platforms to support JIT compilation and can
        run on platforms that disallow execution of dynamically generated code.
    *   Cobalt is a single-process application and does not rely on the ability
        to spawn multiple processes.
    *   Cobalt precompiles a set of shaders that are sufficient to express all
        graphical effects, thereby accommodating platforms that cannot compile
        shaders at runtime.
    *   Cobalt requires a compliant C++11 compiler, allowing it to reach
        platforms with toolchains that don't support the newest C++17 features.

*   **Small footprint**
    *   Cobalt is optimized for memory. Its surface cache never exceeds a
        predefined budget, and it never creates duplicate layers, reducing
        the likelihood of out-of-memory crashes.
    *   Cobalt's small binary is designed to take up as little space as
        possible. By supporting a subset of HTML5/CSS/JS, Cobalt's reduced
        package size even allows bundling of CJK fonts on low-end devices.

*   **Reduced input latency**

    *   Cobalt produces consistent 60FPS animations by only supporting
        animation of properties that don't affect layout, like `transform`,
        and always running animations on a separate thread.
    *   Cobalt is optimized to run on single-core CPUs, resulting in better
        input latency since the renderer and resource loader do not compete
        with layout operations.
    *   On platforms that support GLES2, Cobalt avoids CPU painting by
        performing almost all rendering operations on the GPU.

## Getting started

### Porters

Porters should begin with the [porting guide](starboard/porting.md),
which explains how to use Starboard, Cobalt's porting layer, to customize the
platform-specific functionality that Cobalt uses. There are several reference
documents to help porters customize configuration files and to implement
module-specific functionality. The [Testing with
NPLB](starboard/testing.md) document provides an overview of
Starboard's compliance test suite.

### Developers

Developers can follow the setup instructions for
[Linux](development/setup-linux.md) or
[RasPi](development/setup-raspi.md) to set up their Cobalt development
environment, clone a copy of the Cobalt code repository, and build a Cobalt
binary. The [Cobalt support](development/reference/supported-features.md)
guide lists the HTML elements, CSS properties, CSS selectors, and JavaScript Web
APIs that developers can use in their Cobalt applications.