Name SGIS_color_range Name Strings GLX_SGIS_color_range GL_SGIS_color_range Version $Date: 1999/06/23 23:25:41 $ $Revision: 1.9 $ Number 115 Dependencies OpenGL 1.1 is required SGIX_fbconfig is required SGIX_fbconfig_float is recommended EXT_histogram affects the definition of this extension SGI_color_table affects the definition of this extension SGIS_multisample affects the definition of this extension Overview This extension enhances the fbconfig types to support fbconfigs (visuals) with extended range color data. The range of color data is extended from [0,1] to [min,max], e.g., [-1.5,4.0]. Most OpenGL data paths which clamp colors to [0,1] are modified to clamp colors to [min,max]. The range is a fixed property of the fbconfig. Extended range color is useful for imaging calculations and multipass shading operations which often require signed data or increased dynamic range. IP Status Silicon Graphics has filed for patent protection for some of the techniques described in this extension document. Issues * how does an application request 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? They are interpreted uniquely. An fbconfig is chosen with the tightest possible bound which meets or exceeds the range indicated by the application. * the spec does not distinguish between old-style [0,1] color and extended range color (i.e. no attribute bits, just the min and max values). Is this okay? NO!!! Added EXTENDED_RANGE_SGI attribute to distinguish extended range visuals from other visuals. * 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? YES. * when the color range is extended this implies that accumulation buffers and texture colors also support the extended range. Is this okay? it has been suggested that accumulation stay as [-1,1] which would imply that out of range results would leave the acbuf undefined? * 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? no, alpha is 1.0 * treatment of alpha in general - whenever it would have been set to 1.0 it continues to be 1.0 not * do the ONE_MINUS* blend functions change? no. they are still 1.0-x If the resulting value is negative it is clamped to not 0. Same is true for texture environment calculations. * do transparent pixel values need to be embellished? * floating point representations need some more clarification: 1. internal formats (need new extensions for these) 2. logic op (operates on mantissa or on the raw value?) 3. color table lookups (raw bits or clamped[0,1] 4. color indices - not supported 5. GLX_{RGBA}_SIZE - returns number of bits in the representation * float versions of glXGetFBConfigAttribSGIX? YES! * is clamp to [0,1] behavior necessary? it could be useful to have this behavior where colors are used for blend factors in the texture environment and color buffer blending operations. * Is this extension SGI, SGIX, or SGIS? SGIS, because it does not apply to all SGI platforms, however unlike SGIX, is intended for wide acceptance. New Procedures and Functions None New Tokens Accepted by the parameters of GetBooleanv, GetIntegerv, GetFloatv, and GetDoublev, the parameter of glXChooseFBConfigSGIX, and the and parameters of glXChooseFBConfigWithFltSGIX. EXTENDED_RANGE_SGIS 0x85A5 MIN_RED_SGIS 0x85A6 MAX_RED_SGIS 0x85A7 MIN_GREEN_SGIS 0x85A8 MAX_GREEN_SGIS 0x85A9 MIN_BLUE_SGIS 0x85AA MAX_BLUE_SGIS 0x85AB MIN_ALPHA_SGIS 0x85AC MAX_ALPHA_SGIS 0x85AD Accepted by the parameter of glXGetFBConfigAttribSGIX and glXGetFBConfigFltAttribSGIX, the parameter of glXChooseFBConfigSGIX, and the and parameters of glXChooseFBConfigWithFltSGIX: GLX_EXTENDED_RANGE_SGIS 0x???? GLX_MIN_RED_SGIS 0x???? GLX_MAX_RED_SGIS 0x???? GLX_MIN_GREEN_SGIS 0x???? GLX_MAX_GREEN_SGIS 0x???? GLX_MIN_BLUE_SGIS 0x???? GLX_MAX_BLUE_SGIS 0x???? GLX_MIN_ALPHA_SGIS 0x???? GLX_MAX_ALPHA_SGIS 0x???? Additions to Chapter 2 of the 1.1 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 component may take on in the framebuffer. The three component variants of the color command set A to 1.0 Section 2.13 Colors and Coloring Unsigned integer colors are still scaled to the range [0,1] and thus cannot directly represent colors outside the range [0,1]. Signed integer and floating-point colors can be used to represent colors outside the range [0,1]. Section 2.13.6 (Clamping or Masking) After lighting, RGBA colors are clamped to the range [min, max]. Section 2.13.9 (Final Color Processing) For an RGBA color, each color component (which lies in [min,max]) is converted (by rounding to nearest) to a value with m bits. If the value is fixed-point we assume that the 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. [XXX what should we assume if the value is not a fixed point value?] [XXXare 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 1.1 Specification (Rasterization) Section 3.6.3 (Rasterization of Pixel Rectangles) 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 [0,1]. 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 where t is an integer one less than the size of the corresponding table, and, for each element, an address is found by rounding 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 [0,1], 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. The color components used to index the histogram are clamped, the original values are passed through unmodified to the min/max stage. Color Table The color components of each group that are being replaced by table values are converted to indices by clamping the components to [0,1], multiplying each by t, 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 3.8.5 (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 1.1 Specification (Per-Fragment Operations and the Frame buffer) Color buffers consist of either unsigned integer color indices or R, G, B, and , optionally A unsigned or signed integer values. [XXXfloating point] 4.1.2.5 Multisample Fragment Operations If SAMPLE_ALPHA_TO_MASK_SGIS is enabled, the fragment alpha value used for mask conversion is clamped to [0,1] before the mask is generated, but the fragment alpha value is left unchanged. If SAMPLE_ALPHA_TO_ONE_SGIS is enabled the fragment alpha is set to 1.0. Section 4.1.3 (Alpha Test) ref 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 2.13.9. 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 clamped 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 floating point then each component is first clamped to [min, max]; if the type is signed integer, then the component is clamped to the more restrictive of [-1,1] and [min,max], otherwise 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 1.1 Specification (Special Functions) None Additions to Chapter 6 of the 1.1 Specification (State and State Requests) None Additions to the GLX Specification [Added to the description of glXChooseFBConfigSGIX ] If GLX_EXTENDED_RANGE_SGIS is specified as True, and if any of GLX_MIN_RED_SGIS, GLX_MAX_RED_SGIS, GLX_MIN_GREEN_SGIS, GLX_MAX_GREEN_SGIS, GLX_MIN_BLUE_SGIS, GLX_MAX_BLUE_SGIS, GLX_MIN_ALPHA_SGIS, or GLX_MAX_ALPHA_SGIS 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. Integer values for MIN and MAX attributes are cast to double precision floating point, which is the internal representation of these attributes. Non-integral values for these attributes may be specified using glXChooseFBConfigWithFltSGIX, which is defined in the SGIX_fbconfig_float GLX extension. The visuals returned by glXChooseFBConfigSGIX are sorted on the basis of color range if and only if GLX_EXTENDED_RANGE_SGIS is specified as True. In that case, color range has a higher precedence than GLX_DEPTH_BITS and a lower precedence than GLX_SAMPLES_SGIS. Extended color range visuals can be specified for both displayable (window) and non-displayable (pixmap) drawables. Extended range visuals are displayed in a device-dependant manner, however for traditional color displays they will typically be clamped to the range [0,1]. [Added to Table 3] Attribute Type Description --------- ---- ----------- GLX_EXTENDED_RANGE_SGIS boolean true if visual is extended range GLX_MIN_RED_SGIS double minimum value of red component GLX_MAX_RED_SGIS double maximum value of red component GLX_MIN_GREEN_SGIS double minimum value of green component GLX_MAX_GREEN_SGIS double maximum value of green component GLX_MIN_BLUE_SGIS double minimum value of blue component GLX_MAX_BLUE_SGIS double maximum value of blue component GLX_MIN_ALPHA_SGIS double minimum value of alpha component GLX_MAX_ALPHA_SGIS double maximum value of alpha component [Added to Table 4] Attribute Default Sorting Criterion --------- ------- ----------------- GLX_EXTENDED_RANGE_SGIS False exact GLX_MIN_RED_SGIS 0.0 range GLX_MAX_RED_SGIS 1.0 range GLX_MIN_GREEN_SGIS 0.0 range GLX_MAX_GREEN_SGIS 1.0 range GLX_MIN_BLUE_SGIS 0.0 range GLX_MAX_BLUE_SGIS 1.0 range GLX_MIN_ALPHA_SGIS 0.0 range GLX_MAX_ALPHA_SGIS 1.0 range range - configs with a [MIN,MAX] range that meets or exceeds the specified range are returned, with precedence given to tighter bounds (that is, less negative MIN and less positive MAX). 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 SGIS_multisample If SGIS_multisample is not implemented, then the references to SAMPLE_ALPHA_TO_MASK_SGIS and SAMPLE_ALPHA_TO_ONE_SGIS are invalid, and should be ignored. Errors None New State None New Implementation Dependent State Get Value Get Command Type Minimum Value Maximum Value --------- ----------- ---- ------------- ------------- EXTENDED_RANGE_SGIS GetBooleanv B MIN_RED_SGIS GetFloatv R - 0.0 MAX_RED_SGIS GetFloatv R+ 1.0 - MIN_GREEN_SGIS GetFloatv R - 0.0 MAX_GREEN_SGIS GetFloatv R+ 1.0 - MIN_BLUE_SGIS GetFloatv R - 0.0 MAX_BLUE_SGIS GetFloatv R+ 1.0 - MIN_ALPHA_SGIS GetFloatv R - 0.0 MAX_ALPHA_SGIS GetFloatv R+ 1.0 -