Name SGIS_detail_texture Name Strings GL_SGIS_detail_texture Version $Date: 1995/07/09 06:48:46 $ $Revision: 1.31 $ Number 21 Dependencies EXT_texture is required EXT_subtexture affects the definition of this extension EXT_copy_texture affects the definition of this extension EXT_texture_object affects the definition of this extension Overview This extension introduces texture magnification filters that blend between the level 0 image and a separately defined "detail" image. The detail image represents the characteristics of the high frequency subband image above the band-limited level 0 image. The detail image is typically a rectangular portion of the subband image which is modified so that it can be repeated without discontinuities along its edges. Detail blending can be enabled for all color channels, for the alpha channel only, or for the red, green, and blue channels only. It is available only for 2D textures. WARNING - Silicon Graphics has filed for patent protection for some of the techniques described in this extension document. Issues * Should detail textures be supported in 1D? 3D? (Currently written to support 2D only) * Is there any need to support detail textures with NEAREST or FILTER4 filtering? (No) * How does detail texture interact with a texture whose minimum LOD image is not layer zero? (Handle this in the LOD extension.) * Should six detail filters be defined, so that the MODE is part of the filter name? (LINEAR_ADD_DETAIL_SGIS, LINEAR_ADD_DETAIL_ALPHA_SGIS, ...) (No) * I have scaled and biased the detail texture value to the range [-1,1] in this specification. I believe that Iris GL scaled and biased to [-0.5,0.5]. The [-1,1] range seems clearer to me, if it allows F() to be limited to [0,1]. Is this acceptable? * Should detail texture objects and 2D texture objects be separate sets, or should it be possible to use the same texture object both as a detail texture and as a 2D texture? (Keep them separate) New Procedures and Functions void DetailTexFuncSGIS(enum target, sizei n, const float* points); void GetDetailTexFuncSGIS(enum target, float* points); New Tokens Accepted by the parameters of GetTexImage, GetTexLevelParameterfv, GetTexLevelParameteriv, GetTexParameterfv, GetTexParameteriv, TexImage2D, TexParameterf, TexParameterfv, TexParameteri, and TexParameteriv. If the corresponding extensions are supported, also accepted by the parameters of TexSubImage2DEXT, CopyTexImage2DEXT, CopyTexSubImage2DEXT, and BindTextureEXT: DETAIL_TEXTURE_2D_SGIS Accepted by the parameters of GetBooleanv, GetIntegerv, GetFloatv, and GetDoublev: DETAIL_TEXTURE_2D_BINDING_SGIS Accepted by the parameter of TexParameteri and TexParameterf, and by the parameter of TexParameteriv and TexParameterfv, when their parameter is TEXTURE_MAG_FILTER: LINEAR_DETAIL_SGIS LINEAR_DETAIL_ALPHA_SGIS LINEAR_DETAIL_COLOR_SGIS Accepted by the parameter of TexParameteri, TexParameterf, TexParameteriv, TexParameterfv, GetTexParameteriv, and GetTexParameterfv: DETAIL_TEXTURE_LEVEL_SGIS DETAIL_TEXTURE_MODE_SGIS Accepted by the parameter of GetTexParameteriv and GetTexParameterfv: DETAIL_TEXTURE_FUNC_POINTS_SGIS Additions to Chapter 2 of the 1.0 Specification (OpenGL Operation) None Additions to Chapter 3 of the 1.0 Specification (Rasterization) GL Specification Table 3.7 is updated as follows: Name Type Legal Values ---- ---- ------------ TEXTURE_WRAP_S integer CLAMP, REPEAT TEXTURE_WRAP_T integer CLAMP, REPEAT TEXTURE_WRAP_R_EXT integer CLAMP, REPEAT TEXTURE_MIN_FILTER integer NEAREST, LINEAR, NEAREST_MIPMAP_NEAREST, NEAREST_MIPMAP_LINEAR, LINEAR_MIPMAP_NEAREST, LINEAR_MIPMAP_LINEAR, FILTER4_SGIS TEXTURE_MAG_FILTER integer NEAREST, LINEAR, FILTER4_SGIS, LINEAR_DETAIL_SGIS, LINEAR_DETAIL_ALPHA_SGIS, LINEAR_DETAIL_COLOR_SGIS TEXTURE_BORDER_COLOR 4 floats any 4 values in [0,1] DETAIL_TEXTURE_LEVEL_SGIS integer any non-positive integer DETAIL_TEXTURE_MODE_SGIS integer ADD, MODULATE Table 3.7: Texture parameters and their values. 3.8.2.1 Texture magnification with detail Three additional texture magnification filters are defined for texture magnification. These values, which are assigned to TEXTURE_MAG_FILTER, are LINEAR_DETAIL_SGIS, LINEAR_DETAIL_ALPHA_SGIS, and LINEAR_DETAIL_COLOR_SGIS. All three filters sample the level zero texture array exactly as it would be sampled with filter mode LINEAR. All three also sample the level zero texture array of a second texture, known as the detail texture, when three conditions are met. The detail texture corresponding to texture TEXTURE_2D is DETAIL_TEXTURE_2D_SGIS. The conditions are: 1. The active texture must be TEXTURE_2D. 2. The internal formats of TEXTURE_2D and DETAIL_TEXTURE_2D_SGIS must have been specified identically. 3. The level 0 array of DETAIL_TEXTURE_2D_SGIS must have nonzero width and height. If these conditions are not met, it is as though the magnification texture filter was LINEAR. (Although querying the magnification filter value will return the value as specified.) If they are met, the level zero array of the detail texture is also linearly sampled, using the following arithmetic: n = log base 2 of the width of the level zero array of TEXTURE_2D m = log base 2 of the height of the level zero array of TEXTURE_2D N = log base 2 of the width of DETAIL_TEXTURE_2D_SGIS M = log base 2 of the height of DETAIL_TEXTURE_2D_SGIS L = DETAIL_TEXTURE_LEVEL_SGIS value of TEXTURE_2D u = s * 2**(n-L) v = t * 2**(m-L) i0 = floor(u - 1/2) mod 2**N j0 = floor(v - 1/2) mod 2**M i1 = (i0 + 1) mod 2**N j1 = (j0 + 1) mod 2**M A = frac(u - 1/2) B = frac(v - 1/2) Tdetail = (1-A) * (1-B) * detail[i0,j0] + A * (1-B) * detail[i1,j0] + (1-A) * B * detail[i0,j1] + A * B * detail[i1,j1] Note that magnification corresponds to negative values of level-of-detail and minification corresponds to positive values. Hence L, the value of the DETAIL_TEXTURE_LEVEL_SGIS parameter of TEXTURE_2D, must be negative. The absolute value of L can be thought of as the number of levels that separate the level 0 image of TEXTURE_2D and the image of DETAIL_TEXTURE_2D, which is replicated as necessary to fill the appropriate number of texels. For example, if L is -2, the detail texture image is replicated as necessary in x and y to form a single image whose dimensions are four times larger than the level zero array of TEXTURE_2D. The texture value computed from the primary texture (Ttexture) and the value computed from the detail texture (Tdetail) are combined in one of two ways to compute the final texture value (T). The values of Ttexture, Tdetail, and T are treated as though they range from 0.0 through 1.0 in these equations. If DETAIL_TEXTURE_MODE_SGIS of TEXTURE_2D is ADD, then T' = Ttexture + F(LOD) * (2*Tdetail-1) / 0 T' < 0 T = < T' 0 <= T' <= 1 \ 1 T' > 1 where F is a function of the level-of-detail parameter LOD, which is represented by the Greek character lambda in the GL specification. In effect, the detail texture is scaled and biased so that its range is [-1,1]. The resulting signed value is scaled by a function of LOD, added to the base texture, and clamped to [0,1]. If DETAIL_TEXTURE_MODE_SGIS or TEXTURE_2D is MODULATE, then T' = Ttexture * (1 + F(LOD) * (2*Tdetail-1)) / 0 T' < 0 T = < T' 0 <= T' <= 1 \ 1 T' > 1 Here again the detail texture is scaled and biased so that its range is [-1,1]. The resulting signed value is scaled by a function of LOD, and biased by 1. This result scales the base texture, which is then clamped to [0,1]. The function F of level-of-detail parameter LOD is specified by calling DetailTexFuncSGIS with set to TEXTURE_2D, pointing at an array of pairs of floating point values, and set to the number of value pairs in . The first value of each value pair in specifies a value of LOD, and the second value of each value pair specifies the corresponding function value. The order in which the points are specified is not significant. The value pairs in completely specify the function, replacing any previous specification that may have existed. Since negative values of LOD correspond to magnification and positive values correspond to minification, the points should have negative values for LOD (though it is not an error to specify positive values). Function F is evaluated by sorting the value pairs specified by DetailTexFuncSGIS by LOD value, then fitting a curve through these points. This curve may be linear between adjacent points, or it may be smoothed, but it will pass exactly through the points, limited only by the resolution of the implementation. The value pair with the lowest LOD value specifies the function value F for all values of LOD less than or equal to that pair's LOD. Likewise, the value pair with the greatest LOD value specifies the function value F for all values of LOD greater than or equal to that pair's LOD. F is undefined if two or more value pairs have the same LOD value. If the texture magnification filter is LINEAR_DETAIL_SGIS, then both the color and the alpha components of T are computed as described in the equations above. If the filter is LINEAR_DETAIL_COLOR_SGIS, then all components of T other than alpha are computed as described above, and the alpha component of T is computed as if the texture magnification filter were LINEAR. Finally, if the filter is LINEAR_DETAIL_ALPHA_SGIS, the alpha component of T is computed as described in the equations above, and all other components of T are computed as if the texture magnification filter were LINEAR. All OpenGL texture commands that accept a target value of TEXTURE_2D also accept the target value DETAIL_TEXTURE_2D_SGIS. These commands operate on and return state of the detail texture just as they do of the 2-dimensional texture. If EXT_texture_object is supported, detail texture objects can be created, operated on, and bound just as their 2D counterparts are. The sets of detail textures and 2D textures are exclusive, however, so it is not possible to use a texture object both as a 2D texture and as a detail texture. By default zero is bound to DETAIL_TEXTURE_2D_SGIS, just as zero is bound to TEXTURE_2D. Specification of a detail texture --------------------------------- A detail texture is specified by calling TexImage2D or CopyTexImage2DEXT with set to DETAIL_TEXTURE_2D_SGIS, set to 0, set to 0, and the other parameters specified to generate the desired image. Minification vs. Magnification ------------------------------ If the magnification filter is given by LINEAR_DETAIL_SGIS, LINEAR_DETAIL_ALPHA_SGIS, or LINEAR_DETAIL_COLOR_SGIS, and the minification filter is given by NEAREST_MIPMAP_NEAREST or LINEAR_MIPMAP_NEAREST, then c = 0.5. The parameter c is used to determine whether minification or magnification filtering is done, as described in Section 3.8.2 of the GL Specification (Texture Magnification). Additions to Chapter 4 of the 1.0 Specification (Per-Fragment Operations and the Framebuffer) None Additions to Chapter 5 of the 1.0 Specification (Special Functions) GetDetailTexFuncSGIS is not included in display lists. Additions to Chapter 6 of the 1.0 Specification (State and State Requests) Although many of the parameter values of a detail texture have no effect on texture operation, they are maintained and may be queried. There is no value associated with the binding point DETAIL_TEXTURE_2D_SGIS, so it is not accepted as the parameter of GetBooleanv, GetIntegerv, GetFloatv, or GetDoublev. The name of the detail texture that is bound to DETAIL_TEXTURE_2D_SGIS is queried by calling GetBooleanv, GetIntegerv, GetFloatv, or GetDoublev with set to DETAIL_TEXTURE_2D_BINDING_SGIS. Zero is returned if no texture has been bound. The number of points in the detail texture function specification of a texture is queried by calling GetTexParameteriv or GetTexParameterfv with set to the target of the desired texture and set to DETAIL_TEXTURE_FUNC_POINTS_SGIS. The function GetDetailTexFuncSGIS returns in all of the points in the detail texture function of texture . Additions to the GLX Specification None GLX Protocol Two new GLX protocol commands are added. DetailTexFuncSGIS 2 12+4*2*n rendering command length 2 2051 rendering command opcode 4 ENUM target 4 INT32 n 4*2*n LISTofFLOAT points GetDetailTexFuncSGIS 1 CARD8 opcode (X assigned) 1 17 GLX opcode (glXVendorPrivateWithReply) 2 4 request length 4 4096 vendor specific opcode 4 GLX_CONTEXT_TAG context tag 4 ENUM target => 1 1 reply 1 unused 2 CARD16 sequence number 4 n reply length, m = n 4 unused 4 CARD32 n 16 unused n*4 LISTofFLOAT32 points Note that n may be zero, indicating that a GL error occurred. Otherwise n must be even and n >= 2. Dependencies on EXT_texture EXT_texture is required. Dependencies on EXT_texture3D None, because detail texture is not specified for 3D textures. This extensions is designed to allow a subsequent extension to define 3D detail textures, however. Dependencies on EXT_subtexture If EXT_subtexture is not implemented, then the references to TexSubImage2DEXT and CopyTexSubImage2DEXT in this file are invalid, and should be ignored. Dependencies on EXT_copy_texture If EXT_copy_texture is not implemented, then the references to CopyTexImage2DEXT and CopyTexSubImage2DEXT in this file are invalid, and should be ignored. Dependencies on EXT_texture_object If EXT_texture_object is not implemented, then the references to BindTextureEXT are invalid, and should be ignored. If EXT_texture_object is implemented, the state values named DETAIL_TEXTURE_LEVEL_SGIS DETAIL_TEXTURE_MODE_SGIS DETAIL_TEXTURE_FUNC_POINTS_SGIS are added to the state vector of each texture object. When an attribute set that includes texture information is popped, the bindings and enables are first restored to their pushed values, then the bound textures have their detail parameters restored to their pushed values. Errors INVALID_VALUE is generated if TexImage2D or CopyTexImage2DEXT parameter is DETAIL_TEXTURE_2D_SGIS, and parameter or parameter is not zero. INVALID_VALUE is generated if BindTextureEXT parameter is DETAIL_TEXTURE_2D_SGIS, and parameter is not the name of a detail texture, the name of an as yet unbound texture, or zero. INVALID_VALUE is generated if TexParameteri, TexParameterf, TexParameteriv, or TexParameterfv parameter is DETAIL_TEXTURE_MODE_SGIS, and parameter is not ADD or MODULATE, or parameter doesn't point to ADD or MODULATE. INVALID_VALUE is generated if TexParameteri, TexParameterf, TexParameteriv, or TexParameterfv parameter is DETAIL_TEXTURE_LEVEL_SGIS, and parameter is positive, or parameter points to a positive value. INVALID_ENUM is generated if DetailTexFuncSGIS or GetDetailTexFuncSGIS parameter is not TEXTURE_2D. INVALID_VALUE is generated if DetailTexFuncSGIS parameter is negative. INVALID_OPERATION is generated if DetailTexFuncSGIS or GetDetailTexFuncSGIS is executed between execution of Begin and the corresponding execution to End. New State Get Value Get Command Type Initial Value Attribute --------- ----------- ---- ------------- --------- DETAIL_TEXTURE_2D_BINDING_SGIS GetIntegerv Z+ 0 texture DETAIL_TEXTURE_LEVEL_SGIS GetTexParameteriv n x Z- -4 texture DETAIL_TEXTURE_MODE_SGIS GetTexParameteriv n x Z2 ADD texture DETAIL_TEXTURE_FUNC_POINTS_SGIS GetTexParameteriv n x Z+ 2 texture GetDetailTexFuncSGIS n x m x R {0, 0}, {-4, 1} texture New Implementation Dependent State None