High-level design overview

High-level design overview {#gapi_hld}

G-API High-level design overview

G-API is a heterogeneous framework and provides an unified API to
program image processing pipelines with a number of supported
backends.

The key design idea is to keep pipeline code itself platform-neutral
while specifying which kernels to use and which devices to utilize
using extra parameters at graph compile (configuration) time. This
requirement has led to the following architecture:

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There are three layers in this architecture:

• API Layer – this is the top layer, which implements G-API
  public interface, its building blocks and semantics.
  When user constructs a pipeline with G-API, he interacts with this
  layer directly, and the entities the user operates on (like cv::GMat
  or cv::GComputation) are provided by this layer.
• Graph Compiler Layer – this is the intermediate layer which
  unrolls user computation into a graph and then applies a number of
  transformations to it (e.g. optimizations). This layer is built atop
  of [ADE Framework](@ref gapi_detail_ade).
• Backends Layer – this is the lowest level layer, which lists a
  number of Backends. In contrast with the above two layers,
  backends are highly coupled with low-level platform details, with
  every backend standing for every platform. A backend operates on a
  processed graph (coming from the graph compiler) and executes this
  graph optimally for a specific platform or device.

API layer {#gapi_api_layer}

API layer is what user interacts with when defining and using a
pipeline (a Computat