cl_khr_gl_event
cl_khr_gl_event
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cl_khr_gl_event Create an OpenCL event object from a GL sync object.

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cl_khr_gl_event

## Description

This extension enables the function clCreateEventFromGLsyncKHR.

This extension allows creating OpenCL event objects linked to OpenGL fence sync objects, potentially improving efficiency of sharing images and buffers between the two APIs. The companion `GL_ARB_cl_event` OpenGL extension provides the complementary functionality of creating an OpenGL sync object from an OpenCL event object.

In addition, this extension modifies the behavior of clEnqueueAcquireGLObjects and clEnqueueReleaseGLObjects to implicitly guarantee synchronization with an OpenGL context bound in the same thread as the OpenCL context.

If this extension is supported by an implementation, the string `cl_khr_gl_event` will be present in the CL_PLATFORM_EXTENSIONS or CL_DEVICE_EXTENSIONS string described in the table of `param_name` values for clGetDeviceInfo.

## Notes

Event objects can also be used to reflect the status of an OpenGL sync object. The sync object in turn refers to a fence command executing in an OpenGL command stream. This provides another method of coordinating sharing of buffers and images between OpenGL and OpenCL (see section 9.7.6.1).

If the cl_khr_gl_event extension is supported, then the OpenCL implementation will ensure that any such pending OpenGL operations are complete for an OpenGL context bound to the same thread as the OpenCL context. This is referred to as implicit synchronization.

If the `cl_khr_gl_event` extension is supported and the OpenGL context in question supports fence sync objects, completion of OpenGL commands may also be determined by placing a GL fence command after those commands using `glFenceSync`, creating an event from the resulting GL sync object using clCreateEventFromGLsyncKHR, and determining completion of that event object via clEnqueueAcquireGLObjects. This method may be considerably more efficient than calling `glFinish`, and is referred to as `explicit synchronization`. Explicit synchronization is most useful when an OpenGL context bound to another thread is accessing the memory objects.

If the `cl_khr_gl_event` extension is not supported, completion of OpenGL commands may be determined by issuing and waiting for completion of a `glFinish` command on all OpenGL contexts with pending references to these objects. Some implementations may offer other efficient synchronization methods. If such methods exist they will be described in platform-specific documentation.

Note that no synchronization method other than `glFinish` is portable between all OpenGL implementations and all OpenCL implementations. While this is the only way to ensure completion that is portable to all platforms, `glFinish` is an expensive operation and its use should be avoided if the `cl_khr_gl_event` extension is supported on a platform.

## Specification

OpenCL Specification

## Also see

EXTENSION, clCreateEventFromGLsyncKHR

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