Difference between revisions of "NV2A/Vertex Shader"

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

Revision as of 14:57, 21 April 2017

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