Name
APPLE_texture_packed_float
Name Strings
GL_APPLE_texture_packed_float
Contributors
Alexander Rogoyski, Apple Inc
Serge Metral, Apple Inc
Contact
Alexander Rogoyski, Apple Inc (rogoyski 'at' apple.com)
Status
Complete
Version
Last Modified Date: February 13, 2014
Version: 1.0
Number
OpenGL ES Extension #195
Dependencies
Requires OpenGL ES 2.0.
Written against the OpenGL ES 2.0.25 (Nov. 2010) Specification.
OES_texture_half_float affects the definition of this specification.
EXT_texture_storage affects the definition of this specification.
Overview
This extension adds two new 3-component floating-point texture formats
that fit within a single 32-bit word called R11F_G11F_B10F and RGB9_E5
The first RGB format, R11F_G11F_B10F, stores 5 bits of biased exponent
per component in the same manner as 16-bit floating-point formats, but
rather than 10 mantissa bits, the red, green, and blue components have
6, 6, and 5 bits respectively. Each mantissa is assumed to have an
implied leading one except in the denorm exponent case. There is no
sign bit so only non-negative values can be represented. Positive
infinity, positivedenorms, and positive NaN values are representable.
The value of the fourth component returned by a texture fetch is always
1.0.
The second RGB format, RGB9_E5, stores a single 5-bit exponent (biased
up by 15) and three 9-bit mantissas for each respective component.
There is no sign bit so all three components must be non-negative.
The fractional mantissas are stored without an implied 1 to the left
of the decimal point. Neither infinity nor not-a-number (NaN) are
representable in this shared exponent format.
New Procedures and Functions
None
New Tokens
Accepted by the parameter of TexImage2D and TexSubImage2D:
UNSIGNED_INT_10F_11F_11F_REV_APPLE 0x8C3B
UNSIGNED_INT_5_9_9_9_REV_APPLE 0x8C3E
Accepted by the parameter of TexStorage2DEXT:
R11F_G11F_B10F_APPLE 0x8C3A
RGB9_E5_APPLE 0x8C3D
Changes to Chapter 2 of the OpenGL ES 2.0.25 Specification
(OpenGL Operation)
Add two new sections after Section "Floating-Point Computation":
"Unsigned 11-Bit Floating-Point Numbers"
An unsigned 11-bit floating-point number has no sign bit, a 5-bit
exponent (E), and a 6-bit mantissa (M). The value of an unsigned
11-bit floating-point number (represented as an 11-bit unsigned
integer N) is determined by the following:
0.0, if E == 0 and M == 0,
2^-14 * (M / 64), if E == 0 and M != 0,
2^(E-15) * (1 + M/64), if 0 < E < 31,
INF, if E == 31 and M == 0, or
NaN, if E == 31 and M != 0,
where
E = floor(N / 64), and
M = N mod 64.
Implementations are also allowed to use any of the following
alternative encodings:
0.0, if E == 0 and M != 0
2^(E-15) * (1 + M/64) if E == 31 and M == 0
2^(E-15) * (1 + M/64) if E == 31 and M != 0
When a floating-point value is converted to an unsigned 11-bit
floating-point representation, finite values are rounded to the
closest representable finite value. While less accurate,
implementations are allowed to always round in the direction of
zero. This means negative values are converted to zero.
Likewise, finite positive values greater than 65024 (the maximum
finite representable unsigned 11-bit floating-point value) are
converted to 65024. Additionally: negative infinity is converted
to zero; positive infinity is converted to positive infinity; and
both positive and negative NaN are converted to positive NaN.
Any representable unsigned 11-bit floating-point value is legal
as input to a GL command that accepts 11-bit floating-point data.
The result of providing a value that is not a floating-point
number (such as infinity or NaN) to such a command is unspecified,
but must not lead to GL interruption or termination. Providing a
denormalized number or negative zero to GL must yield predictable
results.
"Unsigned 10-Bit Floating-Point Numbers"
An unsigned 10-bit floating-point number has no sign bit, a 5-bit
exponent (E), and a 5-bit mantissa (M). The value of an unsigned
10-bit floating-point number (represented as an 10-bit unsigned
integer N) is determined by the following:
0.0, if E == 0 and M == 0,
2^-14 * (M / 32), if E == 0 and M != 0,
2^(E-15) * (1 + M/32), if 0 < E < 31,
INF, if E == 31 and M == 0, or
NaN, if E == 31 and M != 0,
where
E = floor(N / 32), and
M = N mod 32.
When a floating-point value is converted to an unsigned 10-bit
floating-point representation, finite values are rounded to the
closet representable finite value. While less accurate,
implementations are allowed to always round in the direction of
zero. This means negative values are converted to zero.
Likewise, finite positive values greater than 64512 (the maximum
finite representable unsigned 10-bit floating-point value) are
converted to 64512. Additionally: negative infinity is converted
to zero; positive infinity is converted to positive infinity; and
both positive and negative NaN are converted to positive NaN.
Any representable unsigned 10-bit floating-point value is legal
as input to a GL command that accepts 10-bit floating-point data.
The result of providing a value that is not a floating-point
number (such as infinity or NaN) to such a command is
unspecified, but must not lead to GL interruption or termination.
Providing a denormalized number or negative zero to GL must yield
predictable results.
Changes to Chapter 3 of the OpenGL ES 2.0.25 Specification (Rasterization)
Add to Table 3.2, p. 62:
type Parameter Corresponding Special
Token Name GL Data Type Interpretation
---------------------------------------- ------------- --------------
UNSIGNED_INT_10F_11F_11F_REV_APPLE uint Yes
UNSIGNED_INT_5_9_9_9_REV_APPLE uint Yes
Add to Table 3.4, p. 63:
Format Type Bytes per Pixel
---------------- ------------------------------------ ---------------
RGB UNSIGNED_INT_10F_11F_11F_REV_APPLE 4
RGB UNSIGNED_INT_5_9_9_9_REV_APPLE 4
Add to Table 3.5, p. 64:
type Parameter GL Data Number of Matching
Token Name Type Components Pixel Formats
---------------------------------- ------- ---------- -------------
UNSIGNED_INT_10F_11F_11F_REV_APPLE uint 3 RGB
UNSIGNED_INT_5_9_9_9_REV_APPLE uint 3 RGB
Add the following to section 3.6.2 Transfer of Pixel Rectangles,
subsection Unpacking
UNSIGNED_INT_10F_11F_11F_REV_APPLE:
31 30 ... 23 22 21 20 ... 12 11 10 9 ... 1 0
+---------------+---------------+---------------+
| 3rd | 2nd | 1st |
+---------------+---------------+---------------+
UNSIGNED_INT_5_9_9_9_REV_APPLE:
31 30 ... 27 26 25 24 ... 18 17 16 15 ... 9 8 7 6 5 4 ... 0
+------------+---------------+---------------+---------------+
| 4th | 3rd | 2nd | 1st |
+------------+---------------+---------------+---------------+
Add Section 3.7.14, Shared Exponent Texture Color Conversion
If the currently bound texture's is RGB and is
UNSIGNED_INT_5_9_9_9_REV_APPLE, the red, green, blue, and shared
bits are converted to color components (prior to filtering) using
shared exponent decoding. The 1st, 2nd, 3rd, and 4th components
are called p_red, p_green, p_blue, and p_exp respectively and are
treated as unsigned integers. They are converted to floating-point
red, green, and blue as follows:
red = p_red * 2^(p_exp - B - N)
green = p_green * 2^(p_exp - B - N)
blue = p_blue * 2^(p_exp - B - N)
where B is 15 (the exponent bias) and N is 9 (the number of mantissa
bits)."
Errors
Relaxation of INVALID_ENUM errors
---------------------------------
TexImage2D, and TexSubImage2D accept the new
UNSIGNED_INT_10F_11F_11F_REV_APPLE and
UNSIGNED_INT_5_9_9_9_REV_APPLE token for .
TexStorage2DEXT accepts the new R11F_G11F_B10F_APPLE and
RGB9_E5_APPLE token for .
New errors
----------
INVALID_OPERATION is generated by TexImage2D and TexSubImage2D
if is UNSIGNED_INT_10F_11F_11F_REV_APPLE or
UNSIGNED_INT_5_9_9_9_REV_APPLE and is not RGB.
UNSIGNED_INT_10F_11F_11F_REV_APPLE is implied as the when
TexStorage2DEXT is called with
R11F_G11F_B10F_APPLE. Thus, INVALID_OPERATION is generated by TexSubImage2D
if is not UNSIGNED_INT_10F_11F_11F_REV_APPLE.
UNSIGNED_INT_5_9_9_9_REV_APPLE is implied as the when
TexStorage2DEXT is called with
RGB9_E5_APPLE. Thus, INVALID_OPERATION is generated by TexSubImage2D
if is not UNSIGNED_INT_5_9_9_9_REV_APPLE.
Dependencies on OES_texture_half_float
If OES_texture_half_float is not supported, modify fifth paragraph
of 3.7.1 Texture Image Specification, p. 67:
"The selected groups are processed as described in section 3.6.2, stopping
after final expansion to RGBA. If the internal format of the texture is
fixed-point, components are clamped to [0,1]. Otherwise, values are not
modified."
Modify first sentence of "Unpacking", p. 62:
"Data are taken from client memory as a sequence of one of the GL data
types listed in Table 3.2. These elements are..."
Additionally, ignore all references to RGBA16F_EXT, RGB16F_EXT,
RG16F_EXT, R16F_EXT, HALF_FLOAT_OES and half.
Dependencies on EXT_texture_storage
If EXT_texture_storage is not supported, remove all references to
TexStorage2DEXT.
New Implementation Dependent State
None
Revision History
1.0 2014/02/13 rogoyski Initial version