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Name
NV_triple_buffer
NV_quadruple_buffer
Name Strings
EGL_NV_triple_buffer
EGL_NV_quadruple_buffer
Contributors
Daniel Kartch, NVIDIA Corporation
Tom McReynolds, NVIDIA Corporation
Santanu Thangaraj, NVIDIA Corporation
Contact
Daniel Kartch, NVIDIA Corporation (dkartch 'at' nvidia.com)
Status
Complete.
Version
Version 1 - February 28, 2019
Number
133
Extension Type
EGL display extension
Dependencies
Requires EGL 1.0
This extension is written against the wording of the EGL 1.3
Specification.
Overview
NV_triple_buffer and NV_quadruple_buffer allow applications to
request additional back buffers, in order to produce greater and
less variable frame rates.
This document describes two related extensions, one dependent on
the other. Implementations may choose to support only
NV_triple_buffer and not NV_quadruple_buffer, but not vice versa.
New Types
None
New Procedures and Functions
None
New Tokens
Added by NV_triple_buffer:
Accepted as a value for EGL_RENDER_BUFFER in the <attrib_list>
parameter of eglCreateWindowSurface:
EGL_TRIPLE_BUFFER_NV 0x3230
Added by NV_quadruple_buffer:
Accepted as a value for EGL_RENDER_BUFFER in the <attrib_list>
parameter of eglCreateWindowSurface:
EGL_QUADRUPLE_BUFFER_NV 0x3231
Additions to the EGL 1.3 Specification:
Insert after third sentence of second paragraph of Section 2.2.2
(Rendering Models):
Windows may have more than one back buffer, allowing rendering
of a new frame to proceed while the copy requested by
eglSwapBuffers is still pending.
Replace the third sentence of the EGL_RENDER_BUFFER description in
Section 3.5.1 (Creating On-Screen Rendering Surfaces):
If its value is EGL_BACK_BUFFER, EGL_TRIPLE_BUFFER_NV, or
EGL_QUADRUPLE_BUFFER_NV, then client APIs should render into
the current back buffer. The implementation should provide
at least one, two, or three back buffers, respectively, which
will be used in rotation each frame.
Change first sentence of third bullet point of eglQueryContext
description in Section 3.7.4 (Context Queries):
If the context is bound to a window surface, then either
EGL_SINGLE_BUFFER, EGL_BACK_BUFFER, EGL_TRIPLE_BUFFER_NV, or
EGL_QUADRUPLE_BUFFER_NV may be returned.
Replace first sentence of eglSwapBuffers description in
Section 3.9.1
(Posting to a Window):
If surface is a back-buffered window surface, then the current
color buffer is copied to the native window associated with
that surface. If there is more than one back buffer, then the
next color buffer in rotation becomes current, and rendering
of the next frame may proceed before the copy takes place,
provided any previous swaps from the new current buffer have
completed.
Issues
1. Why do we need triple-buffering?
RESOLVED: With only a single back buffer and a non-zero swap
interval, eglSwapBuffers must block rendering to the back-
buffer until the copy has completed. This can leave the CPU
and/or GPU idle, wasting valuable compute time, and possibly
cause the next frame to be delivered later than otherwise could
have been. Additional buffers allow rendering to continue even
when a frame is awaiting display, maximizing our use of
computational resources.
2. Why quadruple-buffering? Isn't triple-buffering enough to
produce frames as fast as the processor(s) and swap interval
allow?
RESOLVED: When there is only a single rendering stream
operating on a system, triple-buffering is sufficient. However,
if other threads are contending for resources, variable
latencies may be introduced. This is especially problematic
with video, where any deviation in frame rate from the recorded
media can produce visible artifacts. Additional buffers smooth
out these latencies, allowing a steady frame rate.
3. Then why not arbitrary n-buffering?
RESOLVED: The TRIPLE/QUADRUPLE buffer specification fits nicely
into the RENDER_BUFFER attribute already in use for
eglCreateWindowSurface. Arbitrary buffer counts would require a
new attribute. Additionally, case studies indicated no
significant benefit to using more than three back buffers,
especially when factoring in the added memory cost.
Revision History
#2 (February 28, 2019) Santanu Thangaraj
- Marked issues 1,2 and 3 as resolved.
- Included extension type section.
- Corrected line length violations.
#1 (August 12, 2008) Daniel Kartch
- Initial Draft
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