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WGL_ATI_pixel_format_float
WGL_ATI_pixel_format_float
Name Strings
WGL_ATI_pixel_format_float
Contact
Rob Mace, ATI Research (mace 'at' ati.com)
Status
Complete.
Version
Last Modified Date: December 4, 2002
Revision: 5
Number
278
Dependencies
WGL_ARB_pixel_format is required.
This extension is written against the OpenGL 1.3 Specification.
Overview
This extension adds pixel formats with floating-point RGBA color
components.
The size of each float components is specified using the same
WGL_RED_BITS_ARB, WGL_GREEN_BITS_ARB, WGL_BLUE_BITS_ARB and
WGL_ALPHA_BITS_ARB pixel format attributes that are used for
defining the size of fixed-point components. 32 bit floating-
point components are in the standard IEEE float format. 16 bit
floating-point components have 1 sign bit, 5 exponent bits,
and 10 mantissa bits.
In standard OpenGL RGBA color components are normally clamped to
the range [0,1]. The color components of a float buffer are
clamped to the limits of the range representable by their format.
Issues
1. Should we expose a GL_FLOAT16_ATI pixel type?
RESOLUTION: This will be exposed in a separate extension.
None
Accepted by the <pname> parameters of GetBooleanv, GetIntegerv,
GetFloatv, and GetDoublev:
RGBA_FLOAT_MODE_ATI 0x8820
COLOR_CLEAR_UNCLAMPED_VALUE_ATI 0x8835
Accepted as a value in the <piAttribIList> and <pfAttribFList>
parameter arrays of wglChoosePixelFormatARB, and returned in the
<piValues> parameter array of wglGetPixelFormatAttribivARB, and the
<pfValues> parameter array of wglGetPixelFormatAttribfvARB:
WGL_TYPE_RGBA_FLOAT_ATI 0x21A0
Additions to Chapter 2 of the OpenGL 1.3 Specification (OpenGL
Operation)
Add a new Section 2.1.2, (p. 6):
2.1.2 16 Bit Floating-Point
A 16 bit floating-point number has 1 sign bit (s), 5 exponent
bits (e), and 10 mantissa bits (m). The value (v) of a 16 bit
floating-point number is determined by the following pseudo code:
if (e != 0)
v = (-1)^s * 2^(e-15) * 1.m # normalized
else if (f == 0)
v = (-1)^s * 0 # zero
else
v = (-1)^s * 2^(e-14) * 0.m # denormalized
It is acceptable for an implementation to treat denormalized 16 bit
floating-point numbers as zero.
There are no NAN or infinity values for 16 bit floating-point.
Additions to Chapter 3 of the OpenGL 1.3 Specification (Rasterization)
Section 3.6.4, (p. 92), Add to figure 3.7 a block to "final
conversion" for "RGBA float pixel data out" that says "clamp
to float format range".
Section 3.6.4, (p. 102), change the first paragraph of the "Final
Conversion" to:
For a color index, final conversion consists of masking the bits
of the index to the left of the binary point by 2^n - 1, where n
is the number of bits in an index buffer. For RGBA components the
conversion is based on whether the components in the destination
color buffer are fixed-point or floating-point. For fixed-point
destination buffers components are clamped to [0,1]. The resulting
values are converted to fixed-point according to the rules given in
section 2.13.9 (Final Color Processing). For floating-point
destination buffers components are clamped to the limits of the
range representable by the destination format.
Additions to Chapter 4 of the OpenGL 1.3 Specification (Per-Fragment
Operations and the Frame Buffer)
Chapter 4 Introduction, (p. 156), change the first line of the third
paragraph to:
Color buffers consist of either unsigned integer color indices,
RGB and optionally A unsigned integer values, of RGBA floating-
point values.
Section 4.1.7, (p. 162), change the third paragraph of the page to:
Fixed-point destination (framebuffer) components and source
(fragment) components are taken to be values represented according
to the scheme given in section 2.13.9 (Final Color Processing).
Floating-point destination and source components are taken as is.
Constant color components are taken to be floating-point values.
Section 4.1.7, (p. 163), change the forth line of the second paragraph
of "Using BlendFunc" to:
If destination color components are fixed-point, each floating-
point value in this quadruplet is clamped to [0,1] and converted
back to a fixed-point value in the manner described in section
2.13.9.
Section 4.1.8, (p. 165), insert after the first sentence:
Dithering has no effect if the destination color buffer components
are floating-point.
Section 4.1.9, (p. 165), insert after the first sentence:
Logical operation has no effect if the destination color buffer
components are floating-point.
Section 4.2.3, (p. 170), change the third paragraph to:
void ClearColor(float r, float g, float b, float a);
sets the clear value for the color buffers in RGBA mode. When
clearing a fixed-point color buffer each of the specified
components is clamped to [0; 1] and converted to fixed-point
according to the rules of section 2.13.9. When clearing a
floating-point color buffer the specified components are not
clamped.
Section 4.3.2, (p. 176), change the "Conversion of RGBA values" to:
This step applies only if the GL is in RGBA mode, and then only
if format is neither STENCIL INDEX nor DEPTH COMPONENT. The R,
G, B, and A values form a group of elements. When reading from a
fixed-point color buffer each element is taken to be a fixed-point
value in [0; 1] with m bits, where m is the number of bits in the
corresponding color component of the selected buffer (see
section 2.13.9).
Section 4.3.2, (p. 177), change the second paragraph of the "Final
Conversion" to:
For a fixed-point RGBA color buffer, each component is first
clamped to [0,1]. For floating-point RGBA color buffer, components
are not clamped if the <type> is FLOAT, clamped to [0,1] if the
<type> is unsigned, and clamped to [-1,1] if the <type> is signed.
After clamping the appropriate conversion formula from table 4.7
is applied to the component.
Additions to Chapter 5 of the OpenGL 1.3 Specification (Special
Functions)
None
Additions to Chapter 6 of the OpenGL 1.3 Specification (State and
State Requests)
None
Additions to the GLX Specification
This specification is written for WGL.
GLX Protocol
This specification is written for WGL.
Additions to the WGL Specification
Modify the values accepted by WGL_PIXEL_TYPE_ARB to:
WGL_PIXEL_TYPE_ARB
The type of pixel data. This can be set to WGL_TYPE_RGBA_ARB,
WGL_TYPE_RGBA_FLAOT_ARB, or WGL_TYPE_COLORINDEX_ARB.
Dependencies on WGL_ARB_pixel_format
The WGL_ARB_pixel_format extension must be used to determine a
pixel format with float components.
Dependencies on WGL_ARB_extensions_string
Because this extension is a WGL extension, it is not included in
the GL_EXTENSIONS string. Its existence can be determined with
the WGL_ARB_extensions_string extension.
Errors
None
New State
(table 6.19, p227) modify COLOR_CLEAR_VALUE and add
COLOR_CLEAR_UNCLAMPED_VALUE:
Get Value Type Get Command Initial Value Description Section Attribute
------------------------------- ----- ----------- ------------- ------------------ ------- ------------
COLOR_CLEAR_VALUE C GetFloatv 0,0,0,0 Color buffer clear 4.2.3 color-buffer
value (RGBA mode)
clamped to [0,1]
COLOR_CLEAR_UNCLAMPED_VALUE_ATI 4 x R GetFloatv 0,0,0,0 Color buffer clear 4.2.3 color-buffer
value (RGBA mode)
unclamped
(table 6.28, p236) add the following entry:
Get Value Type Get Command Minimum Value Description Section Attribute
-------------------- ----- ------------ ------------- --------------- -------- ----------
RGBA_FLOAT_MODE_ATI B GetBooleanv - True if RGBA 2.7 -
components are
floats
New Implementation Dependent State
None
Revision History
Date: 12/4/2002
Revision: 5
- Added Section 2.1.2 16 Bit Floating-Point.
Date: 9/12/2002
Revision: 4
- Fixed typo, CLEAR_COLOR_VALUE is really COLOR_CLEAR_VALUE.
Date: 9/11/2002
Revision: 3
- Added enum numbers to New Tokens.
- Added CLEAR_COLOR_UNCLAMPED_VALUE_ATI and defined behavior of
CLEAR_COLOR_VALUE.
- Added description of change to figure 3.7.
- Clarified float clamping in section 3.6.4.
Date: 9/9/2002
Revision: 2
- Changed wording of how float clamping is described in Overview.
Date: 9/6/2002
Revision: 1
- First draft for circulation.
Implementation Support
List of OpenGL implementations supporting the WGL_ATI_pixel_format_float extension
Original File
Original text file for the WGL_ATI_pixel_format_float extension
Page generated on Sun Nov 20 18:40:34 2005