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diff --git a/src/gallium/docs/source/tgsi.rst b/src/gallium/docs/source/tgsi.rst new file mode 100644 index 00000000000..65a669d8cfa --- /dev/null +++ b/src/gallium/docs/source/tgsi.rst @@ -0,0 +1,1291 @@ +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 + + +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 |