Graphics Reference
In-Depth Information
Chapter 13
OpenGL ES 3.0 provides a mechanism for the application to wait until
a set of OpenGL ES operations have finished executing on the GPU. You
can synchronize GL operations among multiple graphics contexts and
threads, which can be important in many advanced graphics applications.
For example, you may want to wait for transform feedback results before
using those results in your applications.
In this chapter, we discuss the flush command, the finish command,
and sync objects and fences, including why they are useful and how to
use them to synchronize operations in the graphics pipeline. Finally, we
conclude with an example of using sync objects and fences.
The OpenGL ES 3.0 API inherits the OpenGL client-server model.
The application, or client, issues commands, and these commands are
processed by the OpenGL ES implementation or server. In OpenGL, the
client and the server can reside on different machines over a network.
OpenGL ES also allows the client and server to reside on different
machines but because OpenGL ES targets handheld and embedded
platforms, the client and server will typically be on the same device.
In the client-server model, the commands issued by the client do not
necessarily get sent to the server immediately. If the client and server are
operating over a network, it will be very inefficient to send individual
commands over the network. Instead, the commands can be buffered on the
client side and then issued to the server at a later point in time. To support
this approach, a mechanism is needed that lets the client know when
