Difference between revisions of "NV2A/Vertex Shader"

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=== Functional units ===
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==== Inverse Logic Unit (ILU) ====
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{| class="wikitable"
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|+ILU Operations
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|-
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!Value
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!Meaning
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|-
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|0
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|NOP
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|-
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|1
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|MOV
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|-
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|2
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|RCP
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|-
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|3
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|RCC
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|-
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|4
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|RSQ
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|-
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|5
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|EXP
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|-
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|6
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|LOG
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|-
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|7
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|LIT
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|}
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==== Multiply-Accumulate (MAC) ====
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{| class="wikitable"
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|+MAC Operations
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|-
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!Value
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!Meaning
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|-
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|0
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|NOP
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|-
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|1
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|MOV
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|-
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|2
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|MUL
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|-
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|3
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|ADD
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|-
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|4
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|MAD
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|-
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|5
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|DP3
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|-
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|6
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|DPH
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|-
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|7
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|DP4
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|-
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|8
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|DST
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|-
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|9
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|MIN
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|-
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|10
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|MAX
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|-
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|11
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|SLT
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|-
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|12
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|SGE
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|-
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|13
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|ARL
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|}
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== Related links ==
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 +
* nvidia resources
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** [https://web.archive.org/web/20191214200729/https://www.nvidia.com/attach/6559 WhereIsThatVertexShaderInstruction.pdf] / [https://web.archive.org/web/20191214200738/https://www.nvidia.com/attach/6560 WhereIsThatVertexShaderInstruction.doc]
 +
* [https://github.com/envytools/envytools/blob/master/nvhw/pgraph_celsius_xfrm.c Code which appears to implement bit-accurate emulation of some instructions]{{FIXME|reason=Unconfirmed, needs testing}}
 +
 +
[[Category:NV2A]]

Latest revision as of 23:42, 4 May 2020

The Xbox implements the 2 GL extensions NV_vertex_program and NV_vertex_program1_1 (with some modifications). This article will mainly focus on actual encoding on hardware as the behaviour is mostly outlined in those GL extensions already.

Operating modes

  • Fixed / Programmable
  • Writeable / Read-Only constants
  • Low-constants only / all constants
  • Vertex processing / State program

Registers

Input registers

There are 16 input registers v[0] to v[15].

They normally map to the vertex attributes. However, in the case of vertex state programs, v[0] is fed from LAUNCH_DATA (PGRAPH Methods 0x1E80, 0x1E84, 0x1E88, 0x1E8C for XYZW respectively) instead.

Output registers

11 output registers o[<RegName>] (initialized to XYZ=0x00000000 W=0x3F800000).

Output registers
Index GL Name D3D Name Meaning
0 HPOS oPos Homogeneous clip space position
3 COL0 oD0 Primary color (front-facing)
4 COL1 oD1 Secondary color (front-facing)
5 FOGC oFog Fog coordinate
6 PSIZ oPts Point size
7 BFC0 oB0 Back-facing primary color
8 BFC1 oB1 Back-facing secondary color
9 TEX0 oT0 Texture coordinate set 0
10 TEX1 oT1 Texture coordinate set 1
11 TEX2 oT2 Texture coordinate set 2
12 TEX3 oT3 Texture coordinate set 3

Address register

A0.x exists as documented in the GL extension.

Temporary registers

There are 12 temporary registers: R0 to R11 (initialized to XYZW=0x00000000), as documented in the GL extension. Additionally, o[HPOS] is mirrored as R12 and can be used as source operand; so effectively you have 13 temporaries

Constant space

There are 192 constant registers in two seperate blocks with 96 constants each. They can be accessed through the PGRAPH RDI: select=0x17. Each constant slot is 4x DWORD, ordered as WZYX. Alternatively they can be uploaded through PGRAPH method [FIXME], with 4x DWORD, ordered XYZW.

In nvidia vertex programs only 96 constants are normally accessible. Microsoft exposed the 96 additional constant registers in D3D shaders through c[-96] to c[-1]. This documentation uses the GL terminology instead and expose the new registers as c[96] to c[191]. This means c[0] to c[191] valid.

Instructions

In total, there are 136 instruction slots.

Each slot consists of 16 bytes, we consider those as 4 seperate little-endian DWORDS describing the operation. Word 0 is inused.

Fields
Meaning Word Offset (bits) Size (bits)
ILU Operation 1 25 3
MAC Operation 1 21 4
Constant index 1 13 8
Input index 1 9 4
Source 1 negate 1 8 1
Source 1 swizzle X 1 6 2
Source 1 swizzle Y 1 4 2
Source 1 swizzle Z 1 2 2
Source 1 swizzle W 1 0 2
Source 1 register 2 28 4
Source 1 mux 2 26 2
Source 2 negate 2 25 1
Source 2 swizzle X 2 23 2
Source 2 swizzle Y 2 21 2
Source 2 swizzle Z 2 19 2
Source 2 swizzle W 2 17 2
Source 2 register 2 13 4
Source 2 mux 2 11 2
Source 3 negate 2 10 1
Source 3 swizzle X 2 8 2
Source 3 swizzle Y 2 6 2
Source 3 swizzle Z 2 4 2
Source 3 swizzle W 2 2 2
Source 3 register (Hi) 2 0 2
Source 3 register (Lo) 3 30 2
Source 3 mux 3 28 2
Destination MAC mask 3 24 4
Destination temporary register 3 20 4
Destination ILU mask 3 16 4
Destination overall mask 3 12 4
Destination select 3 11 1
Destination output register 3 3 8
Destination mux 3 2 1
Relative constant addressing 3 1 1
Final instruction marker (EOF) 3 0 1
Swizzle table
Value Meaning
0 X
1 Y
2 Z
3 W

Functional units

Inverse Logic Unit (ILU)

ILU Operations
Value Meaning
0 NOP
1 MOV
2 RCP
3 RCC
4 RSQ
5 EXP
6 LOG
7 LIT

Multiply-Accumulate (MAC)

MAC Operations
Value Meaning
0 NOP
1 MOV
2 MUL
3 ADD
4 MAD
5 DP3
6 DPH
7 DP4
8 DST
9 MIN
10 MAX
11 SLT
12 SGE
13 ARL

Related links

Retrieved from "https://xboxdevwiki.net/index.php?title=NV2A/Vertex_Shader&oldid=6852"