Name
NV_depth_nonlinear
Name Strings
GL_NV_depth_nonlinear
EGL_NV_depth_nonlinear
Contact
Gary King, NVIDIA Corporation (gking 'at' nvidia.com)
Notice
Copyright NVIDIA Corporation, 2005 - 2007.
Status
NVIDIA Proprietary
Version
Last Modified: 2007/03/20
NVIDIA Revision: 1.0
Number
XXXX Not Yet XXXX
Dependencies
Written based on the wording of the OpenGL 2.0 Specification and
EGL 1.2 Specification.
Requires EGL 1.1.
Requires OpenGL-ES 1.0.
OES_framebuffer_object affects the wording of this specification.
Overview
Due to the perspective divide, conventional integer Z-buffers have
a hyperbolic distribution of encodings between the near plane
and the far plane. This can result in inaccurate depth testing,
particularly when the number of depth buffer bits is small
and objects are rendered near the far plane.
Particularly when the number of depth buffer bits is limited
(desirable and/or required in low-memory environments), artifacts
due to this loss of precision may occur even with relatively
modest far plane-to-near plane ratios (e.g., greater than 100:1).
Many attempts have been made to provide alternate encodings for
Z-buffer (or alternate formulations for the stored depth) to
reduce the artifacts caused by perspective division, such as
W-buffers, Z-complement buffers and floating-point 1-Z buffers.
This extension adds a non-linear encoded Z buffer to OpenGL,
which can improve the practically useful range of, e.g. 16-bit
depth buffers by up to a factor of 16, greatly improving depth
test quality in applications where the ratio between the near
and far planes can not be as tightly controlled.
IP Status
NVIDIA Proprietary
New Procedures and Functions
None
New Tokens
Accepted as a valid sized internal format by all functions accepting
sized internal formats with a base format of DEPTH_COMPONENT
DEPTH_COMPONENT16_NONLINEAR_NV 0x8E2C
Accepted by the <attrib_list> parameter of eglChooseConfig and
eglCreatePbufferSurface, and by the <attribute> parameter of
eglGetConfigAttrib
EGL_DEPTH_ENCODING_NV 0x30E2
Accepted as a value in the <attrib_list> parameter of eglChooseConfig
and eglCreatePbufferSurface, and returned in the <value> parameter
of eglGetConfigAttrib
EGL_DEPTH_ENCODING_NONE_NV 0
EGL_DEPTH_ENCODING_NONLINEAR_NV 0x30E3
Changes to the OpenGL 2.0 Specification
Add the following line to table 3.16 (p. 154)
+--------------------------------+-----------------+------+
| Sized Internal Format | Base Internal | D |
| | Format | Bits |
+--------------------------------+-----------------+------+
| DEPTH_COMPONENT16_NONLINEAR_NV | DEPTH_COMPONENT | 16 |
+--------------------------------+-----------------+------+
Changes to the EGL 1.2 Specification
Add the following line to table 3.1 (p. 14)
+--------------------------+------+---------------------------------------+
| Attribute | Type | Notes |
+--------------------------+------+---------------------------------------+
| EGL_DEPTH_ENCODING_NV | enum | Type of depth-buffer encoding employed|
+--------------------------+------+---------------------------------------+
Modify the description of the depth buffer in Section 3.4 (p. 15)
"The depth buffer is used only by OpenGL ES. It contains fragment depth
(Z) information generated during rasterization. EGL_DEPTH_SIZE indicates
the depth of this buffer in bits, and EGL_DEPTH_ENCODING_NV indicates which
alternate depth-buffer encoding (if any) should be used. Legal values for
EGL_DEPTH_ENCODING_NV are: EGL_DONT_CARE, EGL_DEPTH_ENCODING_NONE_NV and
EGL_DEPTH_ENCODING_NONLINEAR_NV."
Add the following line to table 3.4 (p. 20)
+-----------------------+---------------+-----------+-------+----------+
| Attribute | Default | Selection | Sort | Sort |
| | | Criteria | Order | Priority |
+-----------------------+---------------+-----------+-------+----------+
| EGL_DEPTH_ENCODING_NV | EGL_DONT_CARE | Exact | None | - |
+-----------------------+---------------+-------------------+----------+
Issues
None
Revision History
#1.0 - 20.03.2007
Renumbered enumerants. Reformatted to 80 columns.
