Project Reality: Shader Model 3.0 Considerations

The Project Reality Team updated Project Reality to support Shader Model 3. The update gave Project Reality more graphical potential. This post considerations when porting shaders from Shader Model 2 to 3.

Fogging

From Shader Model 3, fogging is no longer fixed-function. You must implement your fogging method in the pixel shader.

Output Register Count

Shader Model 2 vertex shaders have a certain number of output registers for each type of data.

oPos:

1 position

oFog:

1 fog

oPts:

1 point-size

oD#:

2 vertex color

oT#:

8 texture coordinate
In Shader Model 3, you have 12 output registers available for any type of data.

Input Register Format

In Shader Model 2, output registers have different levels of precision.

For example, vertex color registers, like oD#, are 8 bits of unsigned data, in the range of 0-1 in the pixel shader.
When you port vertex colors oD# from Shader Model 2 to 3, you must apply saturate() to the vertex color output.

Register Assignments and Declarations

If you encounter the following asm, with constants not declared in 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: use the : register() to a shader variable to a particular register. You can read more about it here.

// 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;
}