XXX - Not complete yet!!!
Name
SGIX_color_type
Name Strings
GLX_SGIX_color_type
GL_SGIX_color_type
Version
$Date: 1996/10/01 21:31:47 $ $Revision: 1.5 $
Number
89
Dependencies
SGIX_fbconfig is required
SGI_complex affects the definition of this extension
EXT_histogram affects the definition of this extension
SGI_color_table affects the definition of this extension
Overview
This extension enhances the fbconfig types to support extended range
real and complex data types. Complex data formats include storage for
both real and imaginary parts of a color. The ranges of the data types
are extended from [0,1] to [-m0.n0,m1.n1], e.g., [-1.5,4.0]. Most
OpenGL data paths which clamp colors to [0,1] are modified to clamp
colors to [-m0.n0,m1.n1]. These extended range data types are useful for
imaging calculations and multipass shading operations that often require
signed data and/or complex data formats.
Issues
* two concepts are defined in this extension, color components with
extended range and storage for complex color components. I'm not
sure if the range aspect should be separated from the complex
storage aspect -- they both extend GLX so it seemed like a time
saver to group them together
* how does an application specify the color range it needs to represent?
should the min/max values be interpreted specially in ChooseConfig
or should they be of a more limited usefulness exact match style?
* the spec does not distinguish between old-style [0,1] real color
and extend range real color (i.e. no attribute bits). Is this okay?
* float input pixel values and float colors automatically support the
extended range. Integer colors are still scaled to [0,1].
This means that GetIntegerv of an extended range color can not
represent an extended color range. Is this okay?
* when the color range is extended this implies that accumulation buffers
and texture colors also support the extended range. Is this okay?
* if a component isn't stored in the framebuffer (bits == 0) what should
range queries return. 0 seems obvious for R, G, and B, but what about
alpha. If there is no alpha value, should alpha be the max value?
* do transparent pixel values need to be embellished?
* is a complex ClearColor and ClearAccum needed?
New Procedures and Functions
None
New Tokens
Accepted by the parameters of GetBooleanv, GetIntegerv,
GetFloatv, and GetDoublev and accepted by the parameter of
glXChooseFBConfigSGIX:
MIN_RED_SGIX 0x????
MAX_RED_SGIX 0x????
MIN_GREEN_SGIX 0x????
MAX_GREEN_SGIX 0x????
MIN_BLUE_SGIX 0x????
MAX_BLUE_SGIX 0x????
MIN_ALPHA_SGIX 0x????
MAX_ALPHA_SGIX 0x????
Accepted by the parameter of glXGetFBConfigAttribSGIX, and
by the parameter of glXChooseFBConfigSGIX:
GLX_COLOR_TYPE_SGIX 0x????
GLX_MIN_RED_SGIX 0x????
GLX_MAX_RED_SGIX 0x????
GLX_MIN_GREEN_SGIX 0x????
GLX_MAX_GREEN_SGIX 0x????
GLX_MIN_BLUE_SGIX 0x????
GLX_MAX_BLUE_SGIX 0x????
GLX_MIN_ALPHA_SGIX 0x????
GLX_MAX_ALPHA_SGIX 0x????
Returned by glXGetFBConfigAttribSGIX (when is set to
GLX_COLOR_TYPE_SGIX) and accepted by the parameter of
glXChooseFBConfigSGIX (following the GLX_COLOR_TYPE_SGIX token):
GLX_REAL_COLOR_SGIX 0x????
GLX_COMPLEX_COLOR_SGIX 0x????
Additions to Chapter 2 of the 1.0 Specification (OpenGL Operation)
Section 2.7 Vertex Specification
Versions of the Color command that take floating-point values
accept values nominally between and . corresponds
to the minimum value while corresponds to the maximum (machine
dependent) value that a compone tmay take on in th framebuffer.
The three component variants of the color command set A to .
Section 2.12 Colors and Coloring
Integer colors are still scaled to the range [0,1] and thus cannot
directly represent colors outside the range [0,1]. Floating-point
colors can be used to represent colors outside the range [0,1].
Section 2.12.6 (Clamping or Masking)
After lighting, RGBA colors are clamped to the range [min, max].
Section 2.12.9 (Final Color Processing)
For an RGBA color, each color component (which lies in [min,max]) is
converted (by rounding to nearest) to a fixed-point value with m bits
for the each of the real and imaginary parts. We assume that the
fixed-point representation used represents each value
min+(max-min)k/(2^m - 1),
where k is in {0, 1, ..., 2^m - 1}, as k (e.g. is represented
in binary as a string of all ones). m must be at least as large as
the number of bits in the corresponding component of the framebuffer.
If the framebuffer is complex, then m must be at least as large as
the number of bits in the corresponding real or imaginary part of the
component of the framebuffer.
[are the rules for the msbs of unsigned color values matching the
framebuffer components true for color ranges outside [0,1]?]
Additions to Chapter 3 of the 1.0 Specification (Rasterization)
Section 3.6.3 (Rasterization of Pixels)
Final Expansion to RGBA
if a group does not contain an A element, then A is added and set to 1.0.
If any of R, G, or B is missing from the group, each missing element is
assigned a value of 0.0.
RGBA to RGBA Lookup
First, each component is clamped to the range [min,max]. If there is a
table associated with each of the R, G, B, and A component elements:
PIXEL_MAP_R_TO_R for R, PIXEL_MAP_G_TO_G for G, PIXEL_MAP_B_TO_B for B,
and PIXEL_MAP_A_TO_A for A. Each element is multiplied by t/(max-min)
where t is an integer one less than the size of the corresponding table,
and, for each element, and address is found by resounding this value to
the nearest integer. For each element, the addressed value in the
corresponding table replaces the element.
Histogram
If HISTOGRAM_EXT is enabled and the width of the table is non-zero, and
the pixel groups contain RGBA values, then indices Ri, Gi, Bi, and Ai
are derived from the red, green, blue, and alpha components of each
pixel group (without modifying these components) by clamping the
components to [min,max], multiplying each by t/(max-min) where t is one
less than the width of the histogram table, and rounding each to the
nearest integer.
Color Table
The color components of each group that are being replaced by table
values are converted to indices by clamping the components to
[min,max], multiplying each by one t/(max-min) where t is one less than
the width of the color table, and rounding each to the nearest
integer. The component value (R, G, B, or A) is then replaced by the
value in color table indicated in table E14.2, at the computed index.
Final Conversion
For RGBA components each element is clamped to [min,max]. The resulting
values are converted to fixed-point according to the rules given in
section 2.12.9 (Final Color Processing).
Section 3.8 (Texturing)
Each R, G, B, and A value so extracted is clamped to [min,max].
Each of the four values set by TEXTURE_BORDER_COLOR is clamped to lie
in [min,max].
Section 3.8.3 (Texture Environments and Texture Functions)
TEXTURE_ENV_COLOR is set to an RGBA color by providing four
single-precision floating-point values in the range [min,max] (values
outside this range are clamped to it).
R, G, B, and A values after being obtained from a supplied texture image,
are in the range [min, max].
[modifications to table 3.9???]
Section 3.9 (Fog)
Each component of Cf is clamped to [min, max] when specified.
Additions to Chapter 4 of the 1.0 Specification (Per-Fragment Operations
and the Frame buffer)
Color buffers consiste of either unsigned integer color indices or
R, G, B, and , optionally A unsigned or signed integer values. The
values may also consist of real and imaginary parts.
Section 4.1.3 (Alpha Test)
red is clamped to lie in [min, max], and then converted to a fixed-point
value according to the rules given for an A component in section 2.12.9.
Section 4.2.3 (Clearing the Buffers)
void ClearColor(clampf r, clampf g, clampf b, clampf a);
sets the clear value for the color buffers in RGBA mode. Each of the
specified components is clapmed to [min, max] and converted to fixed-point
according to the rules of section 2.12.9.
void ClearAccum(clampf r, clampf g, clampf b, clampf a);
takes four floating-point arguments that are the values, in order, to which
to set the R, G, B, and A values of the accumulation buffer (see the next
section). These values are clamped to the range [min2,max] where min2
= minimum(-1,) when they are specified.
Section 4.2.4 (The Accumulation Buffer)
Accumulation buffer values are taken to be signed values in the range
[min2,max] where min2 = minimum(-1,). Using ACCUM obtains the R, G,
B, and A components from the buffer current selected for
reading (section 4.3.2). Each component, considered as a fixed-point
values in [min,max] (see section 2.12.9) is converted to floating-point.
Each result is then multiplied by value.
The color components operated on by Accum must be clamped only if the
operation is RETURN. In this case, a value sent to the enabled color
buffers is first clamped to [min,max]. Otherwise, results are undefined
if the result of an operation on a color component is too large (in
magnitude) to be represented by the number of available bits.
4.3.2 (Reading Pixels)
Conversion to RGBA values
The R, G, and B (and possibly A) values form a group of elements. Each
element is taken to be a fixed-point value in [min,max] with m bits, where
m is the number of bits in the corresponding color component of the
selected buffer (see section 2.12.9)
Final Conversion
For a component, if the type is FLOAT then each component is first clamped
to [min, max]; if the type is not FLOAT then each component is first
clamped to [0,1]. Then the appropriate conversion formula from Table 4.7
is applied to the component.
Additions to Chapter 5 of the 1.0 Specification (Special Functions)
None
Additions to Chapter 6 of the 1.0 Specification (State and State Requests)
None
Additions to the GLX Specification
[Added to the description of glXChooseFBConfigSGIX ]
If any of GLX_MIN_RED_SGIX, GLX_MAX_RED_SGIX, GLX_MIN_GREEN_SGIX,
GLX_MAX_GREEN_SGIX, GLX_MIN_BLUE_SGIX, GLX_MAX_BLUE_SGIX,
GLX_MIN_ALPHA_SGIX, or GLX_MAX_ALPHA_SGIX are specified in
then the value that follows indicates the minimum or maximum value
which can be represented in the OpenGL pipeline as a color. Any
OpenGL state which stores color values (e.g. current color, texture
data, the color buffer, accumulation buffer, aux buffers, etc) can
represent values between the minimum and maximum range. Values
are specified as integral numerator, denominator pairs (rational
numbers).
If GLX_COLOR_TYPE_SGIX is in then the value that follows
indicates how color values are represented in the framebuffer:
GLX_REAL_COLOR_SGIX specifies that only the real value of each color
component is stored in the color and accumulation buffers.
The actual representation of the data is unspecified, but the
range that can be represented can be queried using the color
component min and max requests.
GLX_COMPLEX_COLOR_SGIX specifies that each color component
is stored as a complex number. The distribution of bits
used to represent the real and imaginary portions of the
complex number are unspecified as is the actual representation
of the data (two's complement, sign magnitude, floating point etc).
GLX_RED_SIZE, GLX_GREEN_SIZE, GLX_BLUE_SIZE, GLX_ALPHA_SIZE
are equal to the sum of the number of framebuffer bits used to store
both the real and imaginary parts.
If an accumulation buffer is present, then it also stores both
real and imaginary parts for each color component present.
GLX_ACCUM_RED_SIZE, GLX_ACCUM_GREEN_SIZE, GLX_ACCUM_BLUE_SIZE, and
GLX_ACCUM_ALPHA_SIZE are equal to the total number of bits used to
store each complex component.
In general, only non-displayable drawable types (e.g. GLXPbuffers) will
be able to be created with FBConfigs which support extended range real or
complex color component types (see GLX_DRAWABLE_TYPE_SGIX).
GLX Protocol
[tbd]
Dependencies on EXT_histogram
If EXT_histogram is not implemented, then the references to
GetHistogramEXT and GetMinmaxEXT in this file are invalid, and should be
ignored.
Dependencies on SGI_color_table
If SGI_color_table is not implemented, then the references to
ColorTableSGI and GetColorTableSGI in this file are invalid, and should
be ignored.
Dependencies on SGI_complex
If SGI_complex is not supported, references to GLX_REAL_COLOR_SGIX,
GLX_COMPLEX_COLOR_SGIX and GLX_COLOR_TYPE_SGIX in this document are
invalid and should be ignored.
Errors
None
New State
None
New Implementation Dependent State
None