nv2a-vsh 0.1.12

Assembler/disassembler for the Xbox nv2a vertex shader

Trivial assembler for the nv2a vertex shader.

The Cg -> vp20 path performs various optimizations that sometimes make it hard to force unusual test conditions. This assembler performs no optimizations, and simply translates operands into machine code.

Instructions

• ADD dst, src1, src2

  • Sum dst = src1 + src2

• ARL a0, src

  • Load address register - a0 = src

• DP3 dst, src1, src2

  • 3-component (xyz) dot product - dst = src1 dotproduct_xyz src2

• DP4 dst, src1, src2

  • 4-component (xyzw) dot product - dst = src1 dotproduct_xyzw src2

• DPH dst, src1, src2

  • Homogenous dot product - dst = src1.x * src2.x + src1.y * src2.y + src1.z * src2.z + src2.w

• DST dst, src1, src2

  • Compute distance vector. src1.yz should be distance squared, src2.yw should be 1.0 / distance

  dst.x = 1.0
  dst.y = src1.y * src2.y
  dst.z = src1.z
  dst.w = src2.w
  

• EXPP dst, src

  • Partial precision 2^x exponentiation.

    x_floor = floorf(src.x)
    dst.x = pow(2.0f, x_floor)
    dst.y = src.x - x_floor
    dst.z = pow(2.0f, src.x)
    dst.w = 1.0f
    

• LIT dst, src

  • Calculate lighting coefficients The src vector should be initialized with:

    src.x = normal dotproduct direction_to_light

    src.y = normal dotproduct light_half_vector

    src.w = power

    kMax = 127.9961f
    
    dst.x = 1.0f
    dst.y = 0.0f
    dst.z = 0.0f
    dst.w = 1.0f
    
    power = clamp(src.w, -kMax, kMax)
    
    if (src.x > 0.0f) {
    
      dst.x = src.x
    
      if (src.y > 0.0f) {
        dst.z = pow(src.y, power)
      }
    
    }
    

• LOGP dst, src

  • Partial precision base 2 logarithm

  dst.x = exponent
  dst.y = mantissa
  dst.z = log2(abs(src.x))
  

• MAD dst, src1, src2, src3

  • Multiplies two sources, then adds a third. dst = src1 * src2 + src3

• MAX dst, src1, src2

  • Returns the component-wise maximum between two vectors. dst.C = max(src1.C, src2.C); for C in {x, y, z, w}

• MIN dst, src1, src2

  • Returns the component-wise minimum between two vectors. dst.C = min(src1.C, src2.C); for C in {x, y, z, w}

• MOV dst, src

  • Assigns the value of one register to another. dst = src

• MUL dst, src1, src2

  • Multiply dst = src1 * src2

• RCC dst, src

  • Compute clamped reciprocal. dst.xyzw = 1 / src[.x] clamped to ~(5.42101e-020f, 1.884467e+019)

• RCP dst, src

  • Compute reciprocal. dst.xyzw = 1 / src[.x]

• RSQ dst, src

  • Compute reciprocal of the square root. dst.xyzw = 1 / sqrt(src[.x])

• SGE dst, src1, src2

  • Per component greater than or equal comparison. dst.C = 1.0 if src1.C >= src2.C else 0.0; for C in {x, y, z, w}

• SLT dst, src1, src2

  • Per component less than comparison. dst.C = 1.0 if src1.C < src2.C else 0.0; for C in {x, y, z, w}

Registers

Temporary registers

• r0 - r11
• r12 - read-only view of the oPos output register

Constant/uniform registers

• c0 - c191

Constant registers may also use relative addressing via bracket syntax. E.g., c[a0 + 12]

Address register

• a0

May only be set via the ARL instruction. E.g., ARL a0, v12

Inputs

• v0, iPos
• v1, iWeight
• v2, iNormal
• v3, iDiffuse
• v4, iSpecular
• v5, iFog
• v6, iPts
• v7, iBackDiffuse
• v8, iBackSpecular
• v9, iTex0
• v10, iTex1
• v11, iTex2
• v12, iTex3
• v13
• v14
• v15

Outputs

• oB0, oBackDiffuse
• oB1, oBackSpecular
• oD0, oDiffuse
• oD1, oSpecular
• oFog
• oPos
• oPts
• oTex0, oT0
• oTex1, oT1
• oTex2, oT2
• oTex3, oT3

Swizzle/destination masks

• xyzw
• rgba

Uniform macros

A simple macro syntax is supported to allow symbolic naming for c-register access. Two types are currently implemented, vector and matrix4.

A vector type aliases a single c register. E.g., to give a symbolic name to c10: #uniform_name vector 10. The macro can then be used in subsequent instructions; e.g., mov r0, #uniform_name.

A matrix4 type aliases a contiguous set of 4 c registers. E.g., to give a symbolic name to a model matrix passed at 'c96': #my_model_matrix matrix4 96. To access the second row: mul r0, v0.y, #my_model_matrix[1].

Operation macros

Higher level operations are supported via macros that expand to multiple instructions.

matmul4x4 - Multiply a 4 element vector by a 4x4 matrix

%matmul4x4 <dst> <read_register> <#matrix4_uniform>

Expands to 4 commands.

%matmul4x4 r0 iPos #model_matrix
------------------------------------
dp4 r0.x, iPos, #model_matrix[0]
dp4 r0.y, iPos, #model_matrix[1]
dp4 r0.z, iPos, #model_matrix[2]
dp4 r0.w, iPos, #model_matrix[3]

norm3 - Normalize a 3-component vector.

%norm3 <dst> <read_register> <read_write_temp_register>

Expands to 3 commands and requires one sacrificial register.

%norm3 r2 iNormal r0
------------------------------------
dp3 r0.x, iNormal, iNormal  ; r0.x = len(normal)^2
rsq r0.w, r0.x  ; r0.w = 1 / len(normal)
mul r2.xyz, iNormal, r0.w  ; r2.xyz = normalized(normal)