4 TGSI, Tungsten Graphics Shader Infrastructure, is an intermediate language
5 for describing shaders. Since Gallium is inherently shaderful, shaders are
6 an important part of the API. TGSI is the only intermediate representation
12 All TGSI instructions, known as *opcodes*, operate on arbitrary-precision
13 floating-point four-component vectors. An opcode may have up to one
14 destination register, known as *dst*, and between zero and three source
15 registers, called *src0* through *src2*, or simply *src* if there is only
18 Some instructions, like :opcode:`I2F`, permit re-interpretation of vector
19 components as integers. Other instructions permit using registers as
20 two-component vectors with double precision; see :ref:`Double Opcodes`.
22 When an instruction has a scalar result, the result is usually copied into
23 each of the components of *dst*. When this happens, the result is said to be
24 *replicated* to *dst*. :opcode:`RCP` is one such instruction.
30 ^^^^^^^^^^^^^^^^^^^^^^^^^
32 These opcodes are guaranteed to be available regardless of the driver being
35 .. opcode:: ARL - Address Register Load
39 dst.x = \lfloor src.x\rfloor
41 dst.y = \lfloor src.y\rfloor
43 dst.z = \lfloor src.z\rfloor
45 dst.w = \lfloor src.w\rfloor
48 .. opcode:: MOV - Move
61 .. opcode:: LIT - Light Coefficients
69 dst.z = (src.x > 0) ? max(src.y, 0)^{clamp(src.w, -128, 128))} : 0
74 .. opcode:: RCP - Reciprocal
76 This instruction replicates its result.
83 .. opcode:: RSQ - Reciprocal Square Root
85 This instruction replicates its result.
89 dst = \frac{1}{\sqrt{|src.x|}}
92 .. opcode:: EXP - Approximate Exponential Base 2
96 dst.x = 2^{\lfloor src.x\rfloor}
98 dst.y = src.x - \lfloor src.x\rfloor
105 .. opcode:: LOG - Approximate Logarithm Base 2
109 dst.x = \lfloor\log_2{|src.x|}\rfloor
111 dst.y = \frac{|src.x|}{2^{\lfloor\log_2{|src.x|}\rfloor}}
113 dst.z = \log_2{|src.x|}
118 .. opcode:: MUL - Multiply
122 dst.x = src0.x \times src1.x
124 dst.y = src0.y \times src1.y
126 dst.z = src0.z \times src1.z
128 dst.w = src0.w \times src1.w
131 .. opcode:: ADD - Add
135 dst.x = src0.x + src1.x
137 dst.y = src0.y + src1.y
139 dst.z = src0.z + src1.z
141 dst.w = src0.w + src1.w
144 .. opcode:: DP3 - 3-component Dot Product
146 This instruction replicates its result.
150 dst = src0.x \times src1.x + src0.y \times src1.y + src0.z \times src1.z
153 .. opcode:: DP4 - 4-component Dot Product
155 This instruction replicates its result.
159 dst = src0.x \times src1.x + src0.y \times src1.y + src0.z \times src1.z + src0.w \times src1.w
162 .. opcode:: DST - Distance Vector
168 dst.y = src0.y \times src1.y
175 .. opcode:: MIN - Minimum
179 dst.x = min(src0.x, src1.x)
181 dst.y = min(src0.y, src1.y)
183 dst.z = min(src0.z, src1.z)
185 dst.w = min(src0.w, src1.w)
188 .. opcode:: MAX - Maximum
192 dst.x = max(src0.x, src1.x)
194 dst.y = max(src0.y, src1.y)
196 dst.z = max(src0.z, src1.z)
198 dst.w = max(src0.w, src1.w)
201 .. opcode:: SLT - Set On Less Than
205 dst.x = (src0.x < src1.x) ? 1 : 0
207 dst.y = (src0.y < src1.y) ? 1 : 0
209 dst.z = (src0.z < src1.z) ? 1 : 0
211 dst.w = (src0.w < src1.w) ? 1 : 0
214 .. opcode:: SGE - Set On Greater Equal Than
218 dst.x = (src0.x >= src1.x) ? 1 : 0
220 dst.y = (src0.y >= src1.y) ? 1 : 0
222 dst.z = (src0.z >= src1.z) ? 1 : 0
224 dst.w = (src0.w >= src1.w) ? 1 : 0
227 .. opcode:: MAD - Multiply And Add
231 dst.x = src0.x \times src1.x + src2.x
233 dst.y = src0.y \times src1.y + src2.y
235 dst.z = src0.z \times src1.z + src2.z
237 dst.w = src0.w \times src1.w + src2.w
240 .. opcode:: SUB - Subtract
244 dst.x = src0.x - src1.x
246 dst.y = src0.y - src1.y
248 dst.z = src0.z - src1.z
250 dst.w = src0.w - src1.w
253 .. opcode:: LRP - Linear Interpolate
257 dst.x = src0.x \times src1.x + (1 - src0.x) \times src2.x
259 dst.y = src0.y \times src1.y + (1 - src0.y) \times src2.y
261 dst.z = src0.z \times src1.z + (1 - src0.z) \times src2.z
263 dst.w = src0.w \times src1.w + (1 - src0.w) \times src2.w
266 .. opcode:: CND - Condition
270 dst.x = (src2.x > 0.5) ? src0.x : src1.x
272 dst.y = (src2.y > 0.5) ? src0.y : src1.y
274 dst.z = (src2.z > 0.5) ? src0.z : src1.z
276 dst.w = (src2.w > 0.5) ? src0.w : src1.w
279 .. opcode:: DP2A - 2-component Dot Product And Add
283 dst.x = src0.x \times src1.x + src0.y \times src1.y + src2.x
285 dst.y = src0.x \times src1.x + src0.y \times src1.y + src2.x
287 dst.z = src0.x \times src1.x + src0.y \times src1.y + src2.x
289 dst.w = src0.x \times src1.x + src0.y \times src1.y + src2.x
292 .. opcode:: FRC - Fraction
296 dst.x = src.x - \lfloor src.x\rfloor
298 dst.y = src.y - \lfloor src.y\rfloor
300 dst.z = src.z - \lfloor src.z\rfloor
302 dst.w = src.w - \lfloor src.w\rfloor
305 .. opcode:: CLAMP - Clamp
309 dst.x = clamp(src0.x, src1.x, src2.x)
311 dst.y = clamp(src0.y, src1.y, src2.y)
313 dst.z = clamp(src0.z, src1.z, src2.z)
315 dst.w = clamp(src0.w, src1.w, src2.w)
318 .. opcode:: FLR - Floor
320 This is identical to :opcode:`ARL`.
324 dst.x = \lfloor src.x\rfloor
326 dst.y = \lfloor src.y\rfloor
328 dst.z = \lfloor src.z\rfloor
330 dst.w = \lfloor src.w\rfloor
333 .. opcode:: ROUND - Round
346 .. opcode:: EX2 - Exponential Base 2
348 This instruction replicates its result.
355 .. opcode:: LG2 - Logarithm Base 2
357 This instruction replicates its result.
364 .. opcode:: POW - Power
366 This instruction replicates its result.
370 dst = src0.x^{src1.x}
372 .. opcode:: XPD - Cross Product
376 dst.x = src0.y \times src1.z - src1.y \times src0.z
378 dst.y = src0.z \times src1.x - src1.z \times src0.x
380 dst.z = src0.x \times src1.y - src1.x \times src0.y
385 .. opcode:: ABS - Absolute
398 .. opcode:: RCC - Reciprocal Clamped
400 This instruction replicates its result.
402 XXX cleanup on aisle three
406 dst = (1 / src.x) > 0 ? clamp(1 / src.x, 5.42101e-020, 1.884467e+019) : clamp(1 / src.x, -1.884467e+019, -5.42101e-020)
409 .. opcode:: DPH - Homogeneous Dot Product
411 This instruction replicates its result.
415 dst = src0.x \times src1.x + src0.y \times src1.y + src0.z \times src1.z + src1.w
418 .. opcode:: COS - Cosine
420 This instruction replicates its result.
427 .. opcode:: DDX - Derivative Relative To X
431 dst.x = partialx(src.x)
433 dst.y = partialx(src.y)
435 dst.z = partialx(src.z)
437 dst.w = partialx(src.w)
440 .. opcode:: DDY - Derivative Relative To Y
444 dst.x = partialy(src.x)
446 dst.y = partialy(src.y)
448 dst.z = partialy(src.z)
450 dst.w = partialy(src.w)
453 .. opcode:: KILP - Predicated Discard
458 .. opcode:: PK2H - Pack Two 16-bit Floats
463 .. opcode:: PK2US - Pack Two Unsigned 16-bit Scalars
468 .. opcode:: PK4B - Pack Four Signed 8-bit Scalars
473 .. opcode:: PK4UB - Pack Four Unsigned 8-bit Scalars
478 .. opcode:: RFL - Reflection Vector
482 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
484 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
486 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
492 Considered for removal.
495 .. opcode:: SEQ - Set On Equal
499 dst.x = (src0.x == src1.x) ? 1 : 0
501 dst.y = (src0.y == src1.y) ? 1 : 0
503 dst.z = (src0.z == src1.z) ? 1 : 0
505 dst.w = (src0.w == src1.w) ? 1 : 0
508 .. opcode:: SFL - Set On False
510 This instruction replicates its result.
518 Considered for removal.
521 .. opcode:: SGT - Set On Greater Than
525 dst.x = (src0.x > src1.x) ? 1 : 0
527 dst.y = (src0.y > src1.y) ? 1 : 0
529 dst.z = (src0.z > src1.z) ? 1 : 0
531 dst.w = (src0.w > src1.w) ? 1 : 0
534 .. opcode:: SIN - Sine
536 This instruction replicates its result.
543 .. opcode:: SLE - Set On Less Equal Than
547 dst.x = (src0.x <= src1.x) ? 1 : 0
549 dst.y = (src0.y <= src1.y) ? 1 : 0
551 dst.z = (src0.z <= src1.z) ? 1 : 0
553 dst.w = (src0.w <= src1.w) ? 1 : 0
556 .. opcode:: SNE - Set On Not Equal
560 dst.x = (src0.x != src1.x) ? 1 : 0
562 dst.y = (src0.y != src1.y) ? 1 : 0
564 dst.z = (src0.z != src1.z) ? 1 : 0
566 dst.w = (src0.w != src1.w) ? 1 : 0
569 .. opcode:: STR - Set On True
571 This instruction replicates its result.
578 .. opcode:: TEX - Texture Lookup
583 .. opcode:: TXD - Texture Lookup with Derivatives
588 .. opcode:: TXP - Projective Texture Lookup
593 .. opcode:: UP2H - Unpack Two 16-Bit Floats
599 Considered for removal.
601 .. opcode:: UP2US - Unpack Two Unsigned 16-Bit Scalars
607 Considered for removal.
609 .. opcode:: UP4B - Unpack Four Signed 8-Bit Values
615 Considered for removal.
617 .. opcode:: UP4UB - Unpack Four Unsigned 8-Bit Scalars
623 Considered for removal.
625 .. opcode:: X2D - 2D Coordinate Transformation
629 dst.x = src0.x + src1.x \times src2.x + src1.y \times src2.y
631 dst.y = src0.y + src1.x \times src2.z + src1.y \times src2.w
633 dst.z = src0.x + src1.x \times src2.x + src1.y \times src2.y
635 dst.w = src0.y + src1.x \times src2.z + src1.y \times src2.w
639 Considered for removal.
642 .. opcode:: ARA - Address Register Add
648 Considered for removal.
650 .. opcode:: ARR - Address Register Load With Round
663 .. opcode:: BRA - Branch
669 Considered for removal.
671 .. opcode:: CAL - Subroutine Call
677 .. opcode:: RET - Subroutine Call Return
681 Potential restrictions:
682 * Only occurs at end of function.
684 .. opcode:: SSG - Set Sign
688 dst.x = (src.x > 0) ? 1 : (src.x < 0) ? -1 : 0
690 dst.y = (src.y > 0) ? 1 : (src.y < 0) ? -1 : 0
692 dst.z = (src.z > 0) ? 1 : (src.z < 0) ? -1 : 0
694 dst.w = (src.w > 0) ? 1 : (src.w < 0) ? -1 : 0
697 .. opcode:: CMP - Compare
701 dst.x = (src0.x < 0) ? src1.x : src2.x
703 dst.y = (src0.y < 0) ? src1.y : src2.y
705 dst.z = (src0.z < 0) ? src1.z : src2.z
707 dst.w = (src0.w < 0) ? src1.w : src2.w
710 .. opcode:: KIL - Conditional Discard
714 if (src.x < 0 || src.y < 0 || src.z < 0 || src.w < 0)
719 .. opcode:: SCS - Sine Cosine
732 .. opcode:: TXB - Texture Lookup With Bias
737 .. opcode:: NRM - 3-component Vector Normalise
741 dst.x = src.x / (src.x \times src.x + src.y \times src.y + src.z \times src.z)
743 dst.y = src.y / (src.x \times src.x + src.y \times src.y + src.z \times src.z)
745 dst.z = src.z / (src.x \times src.x + src.y \times src.y + src.z \times src.z)
750 .. opcode:: DIV - Divide
754 dst.x = \frac{src0.x}{src1.x}
756 dst.y = \frac{src0.y}{src1.y}
758 dst.z = \frac{src0.z}{src1.z}
760 dst.w = \frac{src0.w}{src1.w}
763 .. opcode:: DP2 - 2-component Dot Product
765 This instruction replicates its result.
769 dst = src0.x \times src1.x + src0.y \times src1.y
772 .. opcode:: TXL - Texture Lookup With LOD
777 .. opcode:: BRK - Break
787 .. opcode:: ELSE - Else
792 .. opcode:: ENDIF - End If
797 .. opcode:: PUSHA - Push Address Register On Stack
806 Considered for cleanup.
810 Considered for removal.
812 .. opcode:: POPA - Pop Address Register From Stack
821 Considered for cleanup.
825 Considered for removal.
829 ^^^^^^^^^^^^^^^^^^^^^^^^
831 These opcodes are primarily provided for special-use computational shaders.
832 Support for these opcodes indicated by a special pipe capability bit (TBD).
834 XXX so let's discuss it, yeah?
836 .. opcode:: CEIL - Ceiling
840 dst.x = \lceil src.x\rceil
842 dst.y = \lceil src.y\rceil
844 dst.z = \lceil src.z\rceil
846 dst.w = \lceil src.w\rceil
849 .. opcode:: I2F - Integer To Float
853 dst.x = (float) src.x
855 dst.y = (float) src.y
857 dst.z = (float) src.z
859 dst.w = (float) src.w
862 .. opcode:: NOT - Bitwise Not
875 .. opcode:: TRUNC - Truncate
888 .. opcode:: SHL - Shift Left
892 dst.x = src0.x << src1.x
894 dst.y = src0.y << src1.x
896 dst.z = src0.z << src1.x
898 dst.w = src0.w << src1.x
901 .. opcode:: SHR - Shift Right
905 dst.x = src0.x >> src1.x
907 dst.y = src0.y >> src1.x
909 dst.z = src0.z >> src1.x
911 dst.w = src0.w >> src1.x
914 .. opcode:: AND - Bitwise And
918 dst.x = src0.x & src1.x
920 dst.y = src0.y & src1.y
922 dst.z = src0.z & src1.z
924 dst.w = src0.w & src1.w
927 .. opcode:: OR - Bitwise Or
931 dst.x = src0.x | src1.x
933 dst.y = src0.y | src1.y
935 dst.z = src0.z | src1.z
937 dst.w = src0.w | src1.w
940 .. opcode:: MOD - Modulus
944 dst.x = src0.x \bmod src1.x
946 dst.y = src0.y \bmod src1.y
948 dst.z = src0.z \bmod src1.z
950 dst.w = src0.w \bmod src1.w
953 .. opcode:: XOR - Bitwise Xor
957 dst.x = src0.x \oplus src1.x
959 dst.y = src0.y \oplus src1.y
961 dst.z = src0.z \oplus src1.z
963 dst.w = src0.w \oplus src1.w
966 .. opcode:: SAD - Sum Of Absolute Differences
970 dst.x = |src0.x - src1.x| + src2.x
972 dst.y = |src0.y - src1.y| + src2.y
974 dst.z = |src0.z - src1.z| + src2.z
976 dst.w = |src0.w - src1.w| + src2.w
979 .. opcode:: TXF - Texel Fetch
984 .. opcode:: TXQ - Texture Size Query
989 .. opcode:: CONT - Continue
995 Support for CONT is determined by a special capability bit,
996 ``TGSI_CONT_SUPPORTED``. See :ref:`Screen` for more information.
1000 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
1002 These opcodes are only supported in geometry shaders; they have no meaning
1003 in any other type of shader.
1005 .. opcode:: EMIT - Emit
1010 .. opcode:: ENDPRIM - End Primitive
1018 These opcodes are part of :term:`GLSL`'s opcode set. Support for these
1019 opcodes is determined by a special capability bit, ``GLSL``.
1021 .. opcode:: BGNLOOP - Begin a Loop
1026 .. opcode:: BGNSUB - Begin Subroutine
1031 .. opcode:: ENDLOOP - End a Loop
1036 .. opcode:: ENDSUB - End Subroutine
1041 .. opcode:: NOP - No Operation
1046 .. opcode:: NRM4 - 4-component Vector Normalise
1048 This instruction replicates its result.
1052 dst = \frac{src.x}{src.x \times src.x + src.y \times src.y + src.z \times src.z + src.w \times src.w}
1060 .. opcode:: CALLNZ - Subroutine Call If Not Zero
1065 .. opcode:: IFC - If
1070 .. opcode:: BREAKC - Break Conditional
1079 The double-precision opcodes reinterpret four-component vectors into
1080 two-component vectors with doubled precision in each component.
1082 Support for these opcodes is XXX undecided. :T
1084 .. opcode:: DADD - Add
1088 dst.xy = src0.xy + src1.xy
1090 dst.zw = src0.zw + src1.zw
1093 .. opcode:: DDIV - Divide
1097 dst.xy = src0.xy / src1.xy
1099 dst.zw = src0.zw / src1.zw
1101 .. opcode:: DSEQ - Set on Equal
1105 dst.xy = src0.xy == src1.xy ? 1.0F : 0.0F
1107 dst.zw = src0.zw == src1.zw ? 1.0F : 0.0F
1109 .. opcode:: DSLT - Set on Less than
1113 dst.xy = src0.xy < src1.xy ? 1.0F : 0.0F
1115 dst.zw = src0.zw < src1.zw ? 1.0F : 0.0F
1117 .. opcode:: DFRAC - Fraction
1121 dst.xy = src.xy - \lfloor src.xy\rfloor
1123 dst.zw = src.zw - \lfloor src.zw\rfloor
1126 .. opcode:: DFRACEXP - Convert Number to Fractional and Integral Components
1128 Like the ``frexp()`` routine in many math libraries, this opcode stores the
1129 exponent of its source to ``dst0``, and the significand to ``dst1``, such that
1130 :math:`dst1 \times 2^{dst0} = src` .
1134 dst0.xy = exp(src.xy)
1136 dst1.xy = frac(src.xy)
1138 dst0.zw = exp(src.zw)
1140 dst1.zw = frac(src.zw)
1142 .. opcode:: DLDEXP - Multiply Number by Integral Power of 2
1144 This opcode is the inverse of :opcode:`DFRACEXP`.
1148 dst.xy = src0.xy \times 2^{src1.xy}
1150 dst.zw = src0.zw \times 2^{src1.zw}
1152 .. opcode:: DMIN - Minimum
1156 dst.xy = min(src0.xy, src1.xy)
1158 dst.zw = min(src0.zw, src1.zw)
1160 .. opcode:: DMAX - Maximum
1164 dst.xy = max(src0.xy, src1.xy)
1166 dst.zw = max(src0.zw, src1.zw)
1168 .. opcode:: DMUL - Multiply
1172 dst.xy = src0.xy \times src1.xy
1174 dst.zw = src0.zw \times src1.zw
1177 .. opcode:: DMAD - Multiply And Add
1181 dst.xy = src0.xy \times src1.xy + src2.xy
1183 dst.zw = src0.zw \times src1.zw + src2.zw
1186 .. opcode:: DRCP - Reciprocal
1190 dst.xy = \frac{1}{src.xy}
1192 dst.zw = \frac{1}{src.zw}
1194 .. opcode:: DSQRT - Square Root
1198 dst.xy = \sqrt{src.xy}
1200 dst.zw = \sqrt{src.zw}
1203 Explanation of symbols used
1204 ------------------------------
1211 :math:`|x|` Absolute value of `x`.
1213 :math:`\lceil x \rceil` Ceiling of `x`.
1215 clamp(x,y,z) Clamp x between y and z.
1216 (x < y) ? y : (x > z) ? z : x
1218 :math:`\lfloor x\rfloor` Floor of `x`.
1220 :math:`\log_2{x}` Logarithm of `x`, base 2.
1222 max(x,y) Maximum of x and y.
1225 min(x,y) Minimum of x and y.
1228 partialx(x) Derivative of x relative to fragment's X.
1230 partialy(x) Derivative of x relative to fragment's Y.
1232 pop() Pop from stack.
1234 :math:`x^y` `x` to the power `y`.
1236 push(x) Push x on stack.
1240 trunc(x) Truncate x, i.e. drop the fraction bits.
1247 discard Discard fragment.
1251 target Label of target instruction.
1262 Declares a register that is will be referenced as an operand in Instruction
1265 File field contains register file that is being declared and is one
1268 UsageMask field specifies which of the register components can be accessed
1269 and is one of TGSI_WRITEMASK.
1271 Interpolate field is only valid for fragment shader INPUT register files.
1272 It specifes the way input is being interpolated by the rasteriser and is one
1273 of TGSI_INTERPOLATE.
1275 If Dimension flag is set to 1, a Declaration Dimension token follows.
1277 If Semantic flag is set to 1, a Declaration Semantic token follows.
1279 CylindricalWrap bitfield is only valid for fragment shader INPUT register
1280 files. It specifies which register components should be subject to cylindrical
1281 wrapping when interpolating by the rasteriser. If TGSI_CYLINDRICAL_WRAP_X
1282 is set to 1, the X component should be interpolated according to cylindrical
1286 Declaration Semantic
1287 ^^^^^^^^^^^^^^^^^^^^^^^^
1290 Follows Declaration token if Semantic bit is set.
1292 Since its purpose is to link a shader with other stages of the pipeline,
1293 it is valid to follow only those Declaration tokens that declare a register
1294 either in INPUT or OUTPUT file.
1296 SemanticName field contains the semantic name of the register being declared.
1297 There is no default value.
1299 SemanticIndex is an optional subscript that can be used to distinguish
1300 different register declarations with the same semantic name. The default value
1303 The meanings of the individual semantic names are explained in the following
1306 TGSI_SEMANTIC_POSITION
1307 """"""""""""""""""""""
1309 For vertex shaders, TGSI_SEMANTIC_POSITION indicates the vertex shader
1310 output register which contains the homogeneous vertex position in the clip
1311 space coordinate system. After clipping, the X, Y and Z components of the
1312 vertex will be divided by the W value to get normalized device coordinates.
1314 For fragment shaders, TGSI_SEMANTIC_POSITION is used to indicate that
1315 fragment shader input contains the fragment's window position. The X
1316 component starts at zero and always increases from left to right.
1317 The Y component starts at zero and always increases but Y=0 may either
1318 indicate the top of the window or the bottom depending on the fragment
1319 coordinate origin convention (see TGSI_PROPERTY_FS_COORD_ORIGIN).
1320 The Z coordinate ranges from 0 to 1 to represent depth from the front
1321 to the back of the Z buffer. The W component contains the reciprocol
1322 of the interpolated vertex position W component.
1329 For vertex shader outputs or fragment shader inputs/outputs, this
1330 label indicates that the resister contains an R,G,B,A color.
1332 Several shader inputs/outputs may contain colors so the semantic index
1333 is used to distinguish them. For example, color[0] may be the diffuse
1334 color while color[1] may be the specular color.
1336 This label is needed so that the flat/smooth shading can be applied
1337 to the right interpolants during rasterization.
1341 TGSI_SEMANTIC_BCOLOR
1342 """"""""""""""""""""
1344 Back-facing colors are only used for back-facing polygons, and are only valid
1345 in vertex shader outputs. After rasterization, all polygons are front-facing
1346 and COLOR and BCOLOR end up occupying the same slots in the fragment shader,
1347 so all BCOLORs effectively become regular COLORs in the fragment shader.
1353 The fog coordinate historically has been used to replace the depth coordinate
1354 for generation of fog in dedicated fog blocks. Gallium, however, does not use
1355 dedicated fog acceleration, placing it entirely in the fragment shader
1358 The fog coordinate should be written in ``(f, 0, 0, 1)`` format. Only the first
1359 component matters when writing from the vertex shader; the driver will ensure
1360 that the coordinate is in this format when used as a fragment shader input.
1365 PSIZE, or point size, is used to specify point sizes per-vertex. It should
1366 be in ``(s, 0, 0, 1)`` format, where ``s`` is the (possibly clamped) point size.
1367 Only the first component matters when writing from the vertex shader.
1369 When using this semantic, be sure to set the appropriate state in the
1370 :ref:`rasterizer` first.
1372 TGSI_SEMANTIC_GENERIC
1373 """""""""""""""""""""
1375 Generic semantics are nearly always used for texture coordinate attributes,
1376 in ``(s, t, r, q)`` format. ``t`` and ``r`` may be unused for certain kinds
1377 of lookups, and ``q`` is the level-of-detail bias for biased sampling.
1379 These attributes are called "generic" because they may be used for anything
1380 else, including parameters, texture generation information, or anything that
1381 can be stored inside a four-component vector.
1383 TGSI_SEMANTIC_NORMAL
1384 """"""""""""""""""""
1386 Vertex normal; could be used to implement per-pixel lighting for legacy APIs
1387 that allow mixing fixed-function and programmable stages.
1392 FACE is the facing bit, to store the facing information for the fragment
1393 shader. ``(f, 0, 0, 1)`` is the format. The first component will be positive
1394 when the fragment is front-facing, and negative when the component is
1397 TGSI_SEMANTIC_EDGEFLAG
1398 """"""""""""""""""""""
1404 ^^^^^^^^^^^^^^^^^^^^^^^^
1407 Properties are general directives that apply to the whole TGSI program.
1412 Specifies the fragment shader TGSI_SEMANTIC_POSITION coordinate origin.
1413 The default value is UPPER_LEFT.
1415 If UPPER_LEFT, the position will be (0,0) at the upper left corner and
1416 increase downward and rightward.
1417 If LOWER_LEFT, the position will be (0,0) at the lower left corner and
1418 increase upward and rightward.
1420 OpenGL defaults to LOWER_LEFT, and is configurable with the
1421 GL_ARB_fragment_coord_conventions extension.
1423 DirectX 9/10 use UPPER_LEFT.
1425 FS_COORD_PIXEL_CENTER
1426 """""""""""""""""""""
1428 Specifies the fragment shader TGSI_SEMANTIC_POSITION pixel center convention.
1429 The default value is HALF_INTEGER.
1431 If HALF_INTEGER, the fractionary part of the position will be 0.5
1432 If INTEGER, the fractionary part of the position will be 0.0
1434 Note that this does not affect the set of fragments generated by
1435 rasterization, which is instead controlled by gl_rasterization_rules in the
1438 OpenGL defaults to HALF_INTEGER, and is configurable with the
1439 GL_ARB_fragment_coord_conventions extension.
1441 DirectX 9 uses INTEGER.
1442 DirectX 10 uses HALF_INTEGER.
1446 Texture Sampling and Texture Formats
1447 ------------------------------------
1449 This table shows how texture image components are returned as (x,y,z,w) tuples
1450 by TGSI texture instructions, such as :opcode:`TEX`, :opcode:`TXD`, and
1451 :opcode:`TXP`. For reference, OpenGL and Direct3D conventions are shown as
1454 +--------------------+--------------+--------------------+--------------+
1455 | Texture Components | Gallium | OpenGL | Direct3D 9 |
1456 +====================+==============+====================+==============+
1457 | R | (r, 0, 0, 1) | (r, 0, 0, 1) | (r, 1, 1, 1) |
1458 +--------------------+--------------+--------------------+--------------+
1459 | RG | (r, g, 0, 1) | (r, g, 0, 1) | (r, g, 1, 1) |
1460 +--------------------+--------------+--------------------+--------------+
1461 | RGB | (r, g, b, 1) | (r, g, b, 1) | (r, g, b, 1) |
1462 +--------------------+--------------+--------------------+--------------+
1463 | RGBA | (r, g, b, a) | (r, g, b, a) | (r, g, b, a) |
1464 +--------------------+--------------+--------------------+--------------+
1465 | A | (0, 0, 0, a) | (0, 0, 0, a) | (0, 0, 0, a) |
1466 +--------------------+--------------+--------------------+--------------+
1467 | L | (l, l, l, 1) | (l, l, l, 1) | (l, l, l, 1) |
1468 +--------------------+--------------+--------------------+--------------+
1469 | LA | (l, l, l, a) | (l, l, l, a) | (l, l, l, a) |
1470 +--------------------+--------------+--------------------+--------------+
1471 | I | (i, i, i, i) | (i, i, i, i) | N/A |
1472 +--------------------+--------------+--------------------+--------------+
1473 | UV | XXX TBD | (0, 0, 0, 1) | (u, v, 1, 1) |
1474 | | | [#envmap-bumpmap]_ | |
1475 +--------------------+--------------+--------------------+--------------+
1476 | Z | XXX TBD | (z, z, z, 1) | (0, z, 0, 1) |
1477 | | | [#depth-tex-mode]_ | |
1478 +--------------------+--------------+--------------------+--------------+
1480 .. [#envmap-bumpmap] http://www.opengl.org/registry/specs/ATI/envmap_bumpmap.txt
1481 .. [#depth-tex-mode] the default is (z, z, z, 1) but may also be (0, 0, 0, z)
1482 or (z, z, z, z) depending on the value of GL_DEPTH_TEXTURE_MODE.