Project Reality: Shader Model 3.0 Considerations#

The Project Reality Team (realitymod.com) upgraded Project Reality to support Shader Model 3, unlocking greater graphical potential. This document outlines key considerations when porting shaders from Shader Model 2 to 3.

Fogging#

In Shader Model 3, fogging is no longer a fixed-function operation. You must implement your desired fogging method within the pixel shader.

Output Register Count#

Shader Model 2 vertex shaders have a limited number of output registers for each data type:

oPos:

1 position

oFog:

1 fog

oPts:

1 point-size

oD#:

2 vertex color

oT#:

8 texture coordinate
Shader Model 3 provides 12 output registers, usable for any data type.

Input Register Format#

In Shader Model 2, output registers have varying precision levels.

For example, vertex color registers oD# are 8-bit unsigned data, mapped to the [0, 1] range in the pixel shader.
When porting vertex colors oD# from Shader Model 2 to 3, apply saturate() to the vertex color output to ensure correct clamping.

Register Assignments and Declarations#

If you encounter the following assembly code, where constants are not explicitly declared:

Example ASM#

VertexShader = asm
{
   vs.1.1

   dcl_position0 v0

   add r0.xyz, v0.xzw, -c[0].xyz
   mul r0.xyz, r0.xyz, c[1].xyw // z = 0, w = 1
   add oPos.x, r0.x, -c[1].w
   add oPos.y, r0.y, -c[1].w
   mov oPos.z, r0.z
   mov oPos.w, c[1].w // z = 0, w = 1
   add r1, v0.y, -c[2].x
   mul oD0, r1, c[2].y
   mov oD0.a, c[1].z // z = 0
};

PixelShader = asm
{
   ps.1.1
   mov r0, v0
};

The solution is to use the : register() syntax to bind shader variables to specific registers.

Solution#

// Assign variables to registers because DICE didn't do so in their ASM.
float4 Constant0 : register(c0); // c[0]
float4 Constant1 : register(c1); // c[1]
float4 Constant2 : register(c2); // c[2]

struct APP2PS_ProjectRoad
{
   float4 Pos : POSITION0;
};

struct VS2PS_ProjectRoad
{
   float4 HPos : POSITION;
   float4 Color : TEXCOORD0;
};

// VertexShader
VS2PS_ProjectRoad VS_ProjectRoad(APP2PS_ProjectRoad Input)
{
   VS2PS_ProjectRoad Output = (VS2PS_ProjectRoad)0.0;

   // add r0.xyz, v0.xzw, -c[0].xyz
   // mul r0.xyz, r0.xyz, c[1].xyw // z = 0, w = 1
   float3 ProjPos = Input.Pos.xzw - Constant0.xyz;
   ProjPos *= Constant1.xyw; // z = 0, w = 1

   // add oPos.x, r0.x, -c[1].w
   // add oPos.y, r0.y, -c[1].w
   // mov oPos.z, r0.z
   // mov oPos.w, c[1].w // z = 0, w = 1
   Output.HPos.x = ProjPos.x - Constant1.w;
   Output.HPos.y = ProjPos.y - Constant1.w;
   Output.HPos.z = ProjPos.z;
   Output.HPos.w = Constant1.w; // z = 0, w = 1

   // add r1, v0.y, -c[2].x
   // mul oD0, r1, c[2].y
   // mov oD0.a, c[1].z // z = 0
   float4 Color = Input.Pos.y - Constant2.x;
   Output.Color = Color * Constant2.y;
   Output.Color.a = Constant1.z; // z = 0
   Output.Color = saturate(Output.Color);

   return Output;
}

// PixelShader
float4 PS_ProjectRoad(VS2PS_ProjectRoad Input) : COLOR0
{
   // mov r0, v0
   return Input.Color;
}

Project Reality: Shader Model 3.0 Considerations#

Fogging#

Output Register Count#

Input Register Format#

Register Assignments and Declarations#

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