TGSI ==== TGSI, Tungsten Graphics Shader Infrastructure, is an intermediate language for describing shaders. Since Gallium is inherently shaderful, shaders are an important part of the API. TGSI is the only intermediate representation used by all drivers. Instruction Set --------------- From GL_NV_vertex_program ^^^^^^^^^^^^^^^^^^^^^^^^^ ARL - Address Register Load .. math:: dst.x = \lfloor src.x\rfloor dst.y = \lfloor src.y\rfloor dst.z = \lfloor src.z\rfloor dst.w = \lfloor src.w\rfloor MOV - Move .. math:: dst.x = src.x dst.y = src.y dst.z = src.z dst.w = src.w LIT - Light Coefficients .. math:: dst.x = 1 dst.y = max(src.x, 0) dst.z = (src.x > 0) ? max(src.y, 0)^{clamp(src.w, -128, 128))} : 0 dst.w = 1 RCP - Reciprocal .. math:: dst.x = \frac{1}{src.x} dst.y = \frac{1}{src.x} dst.z = \frac{1}{src.x} dst.w = \frac{1}{src.x} RSQ - Reciprocal Square Root .. math:: dst.x = \frac{1}{\sqrt{|src.x|}} dst.y = \frac{1}{\sqrt{|src.x|}} dst.z = \frac{1}{\sqrt{|src.x|}} dst.w = \frac{1}{\sqrt{|src.x|}} EXP - Approximate Exponential Base 2 .. math:: dst.x = 2^{\lfloor src.x\rfloor} dst.y = src.x - \lfloor src.x\rfloor dst.z = 2^{src.x} dst.w = 1 LOG - Approximate Logarithm Base 2 .. math:: dst.x = \lfloor\log_2{|src.x|}\rfloor dst.y = \frac{|src.x|}{2^{\lfloor\log_2{|src.x|}\rfloor}} dst.z = \log_2{|src.x|} dst.w = 1 MUL - Multiply .. math:: dst.x = src0.x \times src1.x dst.y = src0.y \times src1.y dst.z = src0.z \times src1.z dst.w = src0.w \times src1.w ADD - Add .. math:: dst.x = src0.x + src1.x dst.y = src0.y + src1.y dst.z = src0.z + src1.z dst.w = src0.w + src1.w DP3 - 3-component Dot Product .. math:: dst.x = src0.x \times src1.x + src0.y \times src1.y + src0.z \times src1.z dst.y = src0.x \times src1.x + src0.y \times src1.y + src0.z \times src1.z dst.z = src0.x \times src1.x + src0.y \times src1.y + src0.z \times src1.z dst.w = src0.x \times src1.x + src0.y \times src1.y + src0.z \times src1.z DP4 - 4-component Dot Product .. math:: dst.x = src0.x \times src1.x + src0.y \times src1.y + src0.z \times src1.z + src0.w \times src1.w dst.y = src0.x \times src1.x + src0.y \times src1.y + src0.z \times src1.z + src0.w \times src1.w dst.z = src0.x \times src1.x + src0.y \times src1.y + src0.z \times src1.z + src0.w \times src1.w dst.w = src0.x \times src1.x + src0.y \times src1.y + src0.z \times src1.z + src0.w \times src1.w DST - Distance Vector .. math:: dst.x = 1 dst.y = src0.y \times src1.y dst.z = src0.z dst.w = src1.w MIN - Minimum .. math:: dst.x = min(src0.x, src1.x) dst.y = min(src0.y, src1.y) dst.z = min(src0.z, src1.z) dst.w = min(src0.w, src1.w) MAX - Maximum .. math:: dst.x = max(src0.x, src1.x) dst.y = max(src0.y, src1.y) dst.z = max(src0.z, src1.z) dst.w = max(src0.w, src1.w) SLT - Set On Less Than .. math:: dst.x = (src0.x < src1.x) ? 1 : 0 dst.y = (src0.y < src1.y) ? 1 : 0 dst.z = (src0.z < src1.z) ? 1 : 0 dst.w = (src0.w < src1.w) ? 1 : 0 SGE - Set On Greater Equal Than .. math:: dst.x = (src0.x >= src1.x) ? 1 : 0 dst.y = (src0.y >= src1.y) ? 1 : 0 dst.z = (src0.z >= src1.z) ? 1 : 0 dst.w = (src0.w >= src1.w) ? 1 : 0 MAD - Multiply And Add .. math:: dst.x = src0.x \times src1.x + src2.x dst.y = src0.y \times src1.y + src2.y dst.z = src0.z \times src1.z + src2.z dst.w = src0.w \times src1.w + src2.w SUB - Subtract .. math:: dst.x = src0.x - src1.x dst.y = src0.y - src1.y dst.z = src0.z - src1.z dst.w = src0.w - src1.w LRP - Linear Interpolate .. math:: dst.x = src0.x \times src1.x + (1 - src0.x) \times src2.x dst.y = src0.y \times src1.y + (1 - src0.y) \times src2.y dst.z = src0.z \times src1.z + (1 - src0.z) \times src2.z dst.w = src0.w \times src1.w + (1 - src0.w) \times src2.w CND - Condition .. math:: dst.x = (src2.x > 0.5) ? src0.x : src1.x dst.y = (src2.y > 0.5) ? src0.y : src1.y dst.z = (src2.z > 0.5) ? src0.z : src1.z dst.w = (src2.w > 0.5) ? src0.w : src1.w DP2A - 2-component Dot Product And Add .. math:: dst.x = src0.x \times src1.x + src0.y \times src1.y + src2.x dst.y = src0.x \times src1.x + src0.y \times src1.y + src2.x dst.z = src0.x \times src1.x + src0.y \times src1.y + src2.x dst.w = src0.x \times src1.x + src0.y \times src1.y + src2.x FRAC - Fraction .. math:: dst.x = src.x - \lfloor src.x\rfloor dst.y = src.y - \lfloor src.y\rfloor dst.z = src.z - \lfloor src.z\rfloor dst.w = src.w - \lfloor src.w\rfloor CLAMP - Clamp .. math:: dst.x = clamp(src0.x, src1.x, src2.x) dst.y = clamp(src0.y, src1.y, src2.y) dst.z = clamp(src0.z, src1.z, src2.z) dst.w = clamp(src0.w, src1.w, src2.w) FLR - Floor This is identical to ARL. .. math:: dst.x = \lfloor src.x\rfloor dst.y = \lfloor src.y\rfloor dst.z = \lfloor src.z\rfloor dst.w = \lfloor src.w\rfloor ROUND - Round .. math:: dst.x = round(src.x) dst.y = round(src.y) dst.z = round(src.z) dst.w = round(src.w) EX2 - Exponential Base 2 .. math:: dst.x = 2^{src.x} dst.y = 2^{src.x} dst.z = 2^{src.x} dst.w = 2^{src.x} LG2 - Logarithm Base 2 .. math:: dst.x = \log_2{src.x} dst.y = \log_2{src.x} dst.z = \log_2{src.x} dst.w = \log_2{src.x} POW - Power .. math:: dst.x = src0.x^{src1.x} dst.y = src0.x^{src1.x} dst.z = src0.x^{src1.x} dst.w = src0.x^{src1.x} XPD - Cross Product .. math:: dst.x = src0.y \times src1.z - src1.y \times src0.z dst.y = src0.z \times src1.x - src1.z \times src0.x dst.z = src0.x \times src1.y - src1.x \times src0.y dst.w = 1 ABS - Absolute .. math:: dst.x = |src.x| dst.y = |src.y| dst.z = |src.z| dst.w = |src.w| RCC - Reciprocal Clamped XXX cleanup on aisle three .. math:: dst.x = (1 / src.x) > 0 ? clamp(1 / src.x, 5.42101e-020, 1.884467e+019) : clamp(1 / src.x, -1.884467e+019, -5.42101e-020) dst.y = (1 / src.x) > 0 ? clamp(1 / src.x, 5.42101e-020, 1.884467e+019) : clamp(1 / src.x, -1.884467e+019, -5.42101e-020) dst.z = (1 / src.x) > 0 ? clamp(1 / src.x, 5.42101e-020, 1.884467e+019) : clamp(1 / src.x, -1.884467e+019, -5.42101e-020) dst.w = (1 / src.x) > 0 ? clamp(1 / src.x, 5.42101e-020, 1.884467e+019) : clamp(1 / src.x, -1.884467e+019, -5.42101e-020) DPH - Homogeneous Dot Product .. math:: dst.x = src0.x \times src1.x + src0.y \times src1.y + src0.z \times src1.z + src1.w dst.y = src0.x \times src1.x + src0.y \times src1.y + src0.z \times src1.z + src1.w dst.z = src0.x \times src1.x + src0.y \times src1.y + src0.z \times src1.z + src1.w dst.w = src0.x \times src1.x + src0.y \times src1.y + src0.z \times src1.z + src1.w COS - Cosine .. math:: dst.x = \cos{src.x} dst.y = \cos{src.x} dst.z = \cos{src.x} dst.w = \cos{src.x} DDX - Derivative Relative To X .. math:: dst.x = partialx(src.x) dst.y = partialx(src.y) dst.z = partialx(src.z) dst.w = partialx(src.w) DDY - Derivative Relative To Y .. math:: dst.x = partialy(src.x) dst.y = partialy(src.y) dst.z = partialy(src.z) dst.w = partialy(src.w) KILP - Predicated Discard discard PK2H - Pack Two 16-bit Floats TBD PK2US - Pack Two Unsigned 16-bit Scalars TBD PK4B - Pack Four Signed 8-bit Scalars TBD PK4UB - Pack Four Unsigned 8-bit Scalars TBD RFL - Reflection Vector .. math:: dst.x = 2 \times (src0.x \times src1.x + src0.y \times src1.y + src0.z \times src1.z) / (src0.x \times src0.x + src0.y \times src0.y + src0.z \times src0.z) \times src0.x - src1.x dst.y = 2 \times (src0.x \times src1.x + src0.y \times src1.y + src0.z \times src1.z) / (src0.x \times src0.x + src0.y \times src0.y + src0.z \times src0.z) \times src0.y - src1.y dst.z = 2 \times (src0.x \times src1.x + src0.y \times src1.y + src0.z \times src1.z) / (src0.x \times src0.x + src0.y \times src0.y + src0.z \times src0.z) \times src0.z - src1.z dst.w = 1 Considered for removal. SEQ - Set On Equal .. math:: dst.x = (src0.x == src1.x) ? 1 : 0 dst.y = (src0.y == src1.y) ? 1 : 0 dst.z = (src0.z == src1.z) ? 1 : 0 dst.w = (src0.w == src1.w) ? 1 : 0 SFL - Set On False .. math:: dst.x = 0 dst.y = 0 dst.z = 0 dst.w = 0 Considered for removal. SGT - Set On Greater Than .. math:: dst.x = (src0.x > src1.x) ? 1 : 0 dst.y = (src0.y > src1.y) ? 1 : 0 dst.z = (src0.z > src1.z) ? 1 : 0 dst.w = (src0.w > src1.w) ? 1 : 0 SIN - Sine .. math:: dst.x = \sin{src.x} dst.y = \sin{src.x} dst.z = \sin{src.x} dst.w = \sin{src.x} SLE - Set On Less Equal Than .. math:: dst.x = (src0.x <= src1.x) ? 1 : 0 dst.y = (src0.y <= src1.y) ? 1 : 0 dst.z = (src0.z <= src1.z) ? 1 : 0 dst.w = (src0.w <= src1.w) ? 1 : 0 SNE - Set On Not Equal .. math:: dst.x = (src0.x != src1.x) ? 1 : 0 dst.y = (src0.y != src1.y) ? 1 : 0 dst.z = (src0.z != src1.z) ? 1 : 0 dst.w = (src0.w != src1.w) ? 1 : 0 STR - Set On True .. math:: dst.x = 1 dst.y = 1 dst.z = 1 dst.w = 1 TEX - Texture Lookup TBD TXD - Texture Lookup with Derivatives TBD TXP - Projective Texture Lookup TBD UP2H - Unpack Two 16-Bit Floats TBD Considered for removal. UP2US - Unpack Two Unsigned 16-Bit Scalars TBD Considered for removal. UP4B - Unpack Four Signed 8-Bit Values TBD Considered for removal. UP4UB - Unpack Four Unsigned 8-Bit Scalars TBD Considered for removal. X2D - 2D Coordinate Transformation .. math:: dst.x = src0.x + src1.x \times src2.x + src1.y \times src2.y dst.y = src0.y + src1.x \times src2.z + src1.y \times src2.w dst.z = src0.x + src1.x \times src2.x + src1.y \times src2.y dst.w = src0.y + src1.x \times src2.z + src1.y \times src2.w Considered for removal. From GL_NV_vertex_program2 ^^^^^^^^^^^^^^^^^^^^^^^^^^ ARA - Address Register Add TBD Considered for removal. ARR - Address Register Load With Round .. math:: dst.x = round(src.x) dst.y = round(src.y) dst.z = round(src.z) dst.w = round(src.w) BRA - Branch pc = target Considered for removal. CAL - Subroutine Call push(pc) pc = target RET - Subroutine Call Return pc = pop() Potential restrictions: * Only occurs at end of function. SSG - Set Sign .. math:: dst.x = (src.x > 0) ? 1 : (src.x < 0) ? -1 : 0 dst.y = (src.y > 0) ? 1 : (src.y < 0) ? -1 : 0 dst.z = (src.z > 0) ? 1 : (src.z < 0) ? -1 : 0 dst.w = (src.w > 0) ? 1 : (src.w < 0) ? -1 : 0 CMP - Compare .. math:: dst.x = (src0.x < 0) ? src1.x : src2.x dst.y = (src0.y < 0) ? src1.y : src2.y dst.z = (src0.z < 0) ? src1.z : src2.z dst.w = (src0.w < 0) ? src1.w : src2.w KIL - Conditional Discard .. math:: if (src.x < 0 || src.y < 0 || src.z < 0 || src.w < 0) discard endif SCS - Sine Cosine .. math:: dst.x = \cos{src.x} dst.y = \sin{src.x} dst.z = 0 dst.y = 1 TXB - Texture Lookup With Bias TBD NRM - 3-component Vector Normalise .. math:: dst.x = src.x / (src.x \times src.x + src.y \times src.y + src.z \times src.z) dst.y = src.y / (src.x \times src.x + src.y \times src.y + src.z \times src.z) dst.z = src.z / (src.x \times src.x + src.y \times src.y + src.z \times src.z) dst.w = 1 DIV - Divide .. math:: dst.x = \frac{src0.x}{src1.x} dst.y = \frac{src0.y}{src1.y} dst.z = \frac{src0.z}{src1.z} dst.w = \frac{src0.w}{src1.w} DP2 - 2-component Dot Product .. math:: dst.x = src0.x \times src1.x + src0.y \times src1.y dst.y = src0.x \times src1.x + src0.y \times src1.y dst.z = src0.x \times src1.x + src0.y \times src1.y dst.w = src0.x \times src1.x + src0.y \times src1.y TXL - Texture Lookup With LOD TBD BRK - Break TBD IF - If TBD BGNFOR - Begin a For-Loop dst.x = floor(src.x) dst.y = floor(src.y) dst.z = floor(src.z) if (dst.y <= 0) pc = [matching ENDFOR] + 1 endif Note: The destination must be a loop register. The source must be a constant register. Considered for cleanup / removal. REP - Repeat TBD ELSE - Else TBD ENDIF - End If TBD ENDFOR - End a For-Loop dst.x = dst.x + dst.z dst.y = dst.y - 1.0 if (dst.y > 0) pc = [matching BGNFOR instruction] + 1 endif Note: The destination must be a loop register. Considered for cleanup / removal. ENDREP - End Repeat TBD PUSHA - Push Address Register On Stack push(src.x) push(src.y) push(src.z) push(src.w) Considered for cleanup / removal. POPA - Pop Address Register From Stack dst.w = pop() dst.z = pop() dst.y = pop() dst.x = pop() Considered for cleanup / removal. From GL_NV_gpu_program4 ^^^^^^^^^^^^^^^^^^^^^^^^ Support for these opcodes indicated by a special pipe capability bit (TBD). CEIL - Ceiling .. math:: dst.x = \lceil src.x\rceil dst.y = \lceil src.y\rceil dst.z = \lceil src.z\rceil dst.w = \lceil src.w\rceil I2F - Integer To Float .. math:: dst.x = (float) src.x dst.y = (float) src.y dst.z = (float) src.z dst.w = (float) src.w NOT - Bitwise Not .. math:: dst.x = ~src.x dst.y = ~src.y dst.z = ~src.z dst.w = ~src.w TRUNC - Truncate .. math:: dst.x = trunc(src.x) dst.y = trunc(src.y) dst.z = trunc(src.z) dst.w = trunc(src.w) SHL - Shift Left .. math:: dst.x = src0.x << src1.x dst.y = src0.y << src1.x dst.z = src0.z << src1.x dst.w = src0.w << src1.x SHR - Shift Right .. math:: dst.x = src0.x >> src1.x dst.y = src0.y >> src1.x dst.z = src0.z >> src1.x dst.w = src0.w >> src1.x AND - Bitwise And .. math:: dst.x = src0.x & src1.x dst.y = src0.y & src1.y dst.z = src0.z & src1.z dst.w = src0.w & src1.w OR - Bitwise Or .. math:: dst.x = src0.x | src1.x dst.y = src0.y | src1.y dst.z = src0.z | src1.z dst.w = src0.w | src1.w MOD - Modulus .. math:: dst.x = src0.x \bmod src1.x dst.y = src0.y \bmod src1.y dst.z = src0.z \bmod src1.z dst.w = src0.w \bmod src1.w XOR - Bitwise Xor .. math:: dst.x = src0.x \oplus src1.x dst.y = src0.y \oplus src1.y dst.z = src0.z \oplus src1.z dst.w = src0.w \oplus src1.w SAD - Sum Of Absolute Differences .. math:: dst.x = |src0.x - src1.x| + src2.x dst.y = |src0.y - src1.y| + src2.y dst.z = |src0.z - src1.z| + src2.z dst.w = |src0.w - src1.w| + src2.w TXF - Texel Fetch TBD TXQ - Texture Size Query TBD CONT - Continue TBD From GL_NV_geometry_program4 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ EMIT - Emit TBD ENDPRIM - End Primitive TBD From GLSL ^^^^^^^^^^ BGNLOOP - Begin a Loop TBD BGNSUB - Begin Subroutine TBD ENDLOOP - End a Loop TBD ENDSUB - End Subroutine TBD NOP - No Operation Do nothing. NRM4 - 4-component Vector Normalise .. math:: dst.x = \frac{src.x}{src.x \times src.x + src.y \times src.y + src.z \times src.z + src.w \times src.w} dst.y = \frac{src.y}{src.x \times src.x + src.y \times src.y + src.z \times src.z + src.w \times src.w} dst.z = \frac{src.z}{src.x \times src.x + src.y \times src.y + src.z \times src.z + src.w \times src.w} dst.w = \frac{src.w}{src.x \times src.x + src.y \times src.y + src.z \times src.z + src.w \times src.w} ps_2_x ^^^^^^^^^^^^ CALLNZ - Subroutine Call If Not Zero TBD IFC - If TBD BREAKC - Break Conditional TBD Double Opcodes ^^^^^^^^^^^^^^^ DADD - Add Double .. math:: dst.xy = src0.xy + src1.xy dst.zw = src0.zw + src1.zw DDIV - Divide Double .. math:: dst.xy = src0.xy / src1.xy dst.zw = src0.zw / src1.zw DSEQ - Set Double on Equal .. math:: dst.xy = src0.xy == src1.xy ? 1.0F : 0.0F dst.zw = src0.zw == src1.zw ? 1.0F : 0.0F DSLT - Set Double on Less than .. math:: dst.xy = src0.xy < src1.xy ? 1.0F : 0.0F dst.zw = src0.zw < src1.zw ? 1.0F : 0.0F DFRAC - Double Fraction .. math:: dst.xy = src.xy - \lfloor src.xy\rfloor dst.zw = src.zw - \lfloor src.zw\rfloor DFRACEXP - Convert Double Number to Fractional and Integral Components .. math:: dst0.xy = frexp(src.xy, dst1.xy) dst0.zw = frexp(src.zw, dst1.zw) DLDEXP - Multiple Double Number by Integral Power of 2 .. math:: dst.xy = ldexp(src0.xy, src1.xy) dst.zw = ldexp(src0.zw, src1.zw) DMIN - Minimum Double .. math:: dst.xy = min(src0.xy, src1.xy) dst.zw = min(src0.zw, src1.zw) DMAX - Maximum Double .. math:: dst.xy = max(src0.xy, src1.xy) dst.zw = max(src0.zw, src1.zw) DMUL - Multiply Double .. math:: dst.xy = src0.xy \times src1.xy dst.zw = src0.zw \times src1.zw DMAD - Multiply And Add Doubles .. math:: dst.xy = src0.xy \times src1.xy + src2.xy dst.zw = src0.zw \times src1.zw + src2.zw DRCP - Reciprocal Double .. math:: dst.xy = \frac{1}{src.xy} dst.zw = \frac{1}{src.zw} DSQRT - Square root double .. math:: dst.xy = \sqrt{src.xy} dst.zw = \sqrt{src.zw} Explanation of symbols used ------------------------------ Functions ^^^^^^^^^^^^^^ :math:`|x|` Absolute value of `x`. :math:`\lceil x \rceil` Ceiling of `x`. clamp(x,y,z) Clamp x between y and z. (x < y) ? y : (x > z) ? z : x :math:`\lfloor x\rfloor` Floor of `x`. :math:`\log_2{x}` Logarithm of `x`, base 2. max(x,y) Maximum of x and y. (x > y) ? x : y min(x,y) Minimum of x and y. (x < y) ? x : y partialx(x) Derivative of x relative to fragment's X. partialy(x) Derivative of x relative to fragment's Y. pop() Pop from stack. :math:`x^y` `x` to the power `y`. push(x) Push x on stack. round(x) Round x. trunc(x) Truncate x, i.e. drop the fraction bits. Keywords ^^^^^^^^^^^^^ discard Discard fragment. dst First destination register. dst0 First destination register. pc Program counter. src First source register. src0 First source register. src1 Second source register. src2 Third source register. target Label of target instruction. Other tokens --------------- Declaration Semantic ^^^^^^^^^^^^^^^^^^^^^^^^ Follows Declaration token if Semantic bit is set. Since its purpose is to link a shader with other stages of the pipeline, it is valid to follow only those Declaration tokens that declare a register either in INPUT or OUTPUT file. SemanticName field contains the semantic name of the register being declared. There is no default value. SemanticIndex is an optional subscript that can be used to distinguish different register declarations with the same semantic name. The default value is 0. The meanings of the individual semantic names are explained in the following sections. TGSI_SEMANTIC_POSITION """""""""""""""""""""" Position, sometimes known as HPOS or WPOS for historical reasons, is the location of the vertex in space, in ``(x, y, z, w)`` format. ``x``, ``y``, and ``z`` are the Cartesian coordinates, and ``w`` is the homogenous coordinate and used for the perspective divide, if enabled. As a vertex shader output, position should be scaled to the viewport. When used in fragment shaders, position will --- XXX --- wait a minute. Should position be in [0,1] for x and y? XXX additionally, is there a way to configure the perspective divide? it's accelerated on most chipsets AFAIK... Position, if not specified, usually defaults to ``(0, 0, 0, 1)``, and can be partially specified as ``(x, y, 0, 1)`` or ``(x, y, z, 1)``. XXX usually? can we solidify that? TGSI_SEMANTIC_COLOR """"""""""""""""""" Colors are used to, well, color the primitives. Colors are always in ``(r, g, b, a)`` format. If alpha is not specified, it defaults to 1. TGSI_SEMANTIC_BCOLOR """""""""""""""""""" Back-facing colors are only used for back-facing polygons, and are only valid in vertex shader outputs. After rasterization, all polygons are front-facing and COLOR and BCOLOR end up occupying the same slots in the fragment, so all BCOLORs effectively become regular COLORs in the fragment shader. TGSI_SEMANTIC_FOG """"""""""""""""" The fog coordinate historically has been used to replace the depth coordinate for generation of fog in dedicated fog blocks. Gallium, however, does not use dedicated fog acceleration, placing it entirely in the fragment shader instead. The fog coordinate should be written in ``(f, 0, 0, 1)`` format. Only the first component matters when writing from the vertex shader; the driver will ensure that the coordinate is in this format when used as a fragment shader input. TGSI_SEMANTIC_PSIZE """"""""""""""""""" PSIZE, or point size, is used to specify point sizes per-vertex. It should be in ``(p, n, x, f)`` format, where ``p`` is the point size, ``n`` is the minimum size, ``x`` is the maximum size, and ``f`` is the fade threshold. XXX this is arb_vp. is this what we actually do? should double-check... When using this semantic, be sure to set the appropriate state in the :ref:`rasterizer` first. TGSI_SEMANTIC_GENERIC """"""""""""""""""""" Generic semantics are nearly always used for texture coordinate attributes, in ``(s, t, r, q)`` format. ``t`` and ``r`` may be unused for certain kinds of lookups, and ``q`` is the level-of-detail bias for biased sampling. These attributes are called "generic" because they may be used for anything else, including parameters, texture generation information, or anything that can be stored inside a four-component vector. TGSI_SEMANTIC_NORMAL """""""""""""""""""" Vertex normal; could be used to implement per-pixel lighting for legacy APIs that allow mixing fixed-function and programmable stages. TGSI_SEMANTIC_FACE """""""""""""""""" FACE is the facing bit, to store the facing information for the fragment shader. ``(f, 0, 0, 1)`` is the format. The first component will be positive when the fragment is front-facing, and negative when the component is back-facing. TGSI_SEMANTIC_EDGEFLAG """""""""""""""""""""" XXX no clue