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GL_HELPERINVOCATION(3G) | [FIXME: manual] | GL_HELPERINVOCATION(3G) |
NAME¶
gl_HelperInvocation - indicates whether a fragment shader invocation is a helper invocationDECLARATION¶
in bool gl_HelperInvocation ;.SH "DESCRIPTION" The value gl_HelperInvocation is true if the fragment shader invocation is considered a helper invocation and is false otherwise. A helper invocation is a fragment-shader invocation that is created solely for the purposes of evaluating derivatives for use in non-helper fragment-shader invocations. Such derivatives are computed implicitly in the built-in function texture()(), and explicitly in the derivative functions dFdx()() and dFdy. Fragment shader helper invocations execute the same shader code as non-helper invocations, but will not have side effects that modify the framebuffer or other shader-accessible memory. In particular:•Fragments corresponding to helper invocations are
discarded when shader execution is complete, without updating the
framebuffer.
•Stores to image and buffer variables performed by
helper invocations have no effect on the underlying image or buffer
memory.
•Atomic operations to image, buffer, or atomic
counter variables performed by helper invocations have no effect on the
underlying image or buffer memory. The values returned by such atomic
operations are undefined.
Helper invocations may be generated for pixels not covered by a primitive being
rendered. While fragment shader inputs qualified with centroid are normally
required to be sampled in the intersection of the pixel and the primitive, the
requirement is ignored for such pixels since there is no intersection between
the pixel and primitive.
Helper invocations may also be generated for fragments that are covered by a
primitive being rendered when the fragment is killed by early fragment tests
(using the early_fragment_tests qualifier) or where the implementation is able
to determine that executing the fragment shader would have no effect other
than assisting in computing derivatives for other fragment shader invocations.
The set of helper invocations generated when processing any set of primitives is
implementation dependent.
VERSION SUPPORT¶
OpenGL Shading Language Version | ||||||||||||
Variable Name | 1.10 | 1.20 | 1.30 | 1.40 | 1.50 | 3.30 | 4.00 | 4.10 | 4.20 | 4.30 | 4.40 | 4.50 |
gl_HelperInvocation | - | - | - | - | - | - | - | - | - | - | - | ✔ |
SEE ALSO¶
dFdx(), texture()COPYRIGHT¶
Copyright © 2014 Khronos Group. This material may be distributed subject to the terms and conditions set forth in the Open Publication License, v 1.0, 8 June 1999. http://opencontent.org/openpub/.COPYRIGHT¶
Copyright © 2014 Khronos Group08/26/2014 | [FIXME: source] |