Currently I'm going through some tutorials and learning DX11 on a DX10 machine (though I just ordered a new DX11 compatible computer) by means of setting the D3D_FEATURE_LEVEL_ setting to 10_0 and switching the vertex and pixel shader versions in D3DX11CompileFromFile to "vs_4_0" and "ps_4_0" respectively. This works fine as I'm not using any DX11-only features yet.

I'd like to make it compatible with DX9.0c, which naively I thought I could do by changing the feature level setting to 9_3 or something and taking the vertex/pixel shader versions down to 3 or 2. However, no matter what I change the vertex/pixel shader versions to, it always fails when I try to call D3DX11CompileFromFile to compile the vertex/pixel shader files when I have D3D_FEATURE_LEVEL_9_3 enabled.

Maybe this is due to the the vertex/pixel shader files themselves being incompatible for the lower vertex/pixel shader versions, but I'm not expert enough to say.

My shader files are listed below:

Vertex shader:

cbuffer MatrixBuffer
{
matrix worldMatrix;
matrix viewMatrix;
matrix projectionMatrix;
};

struct VertexInputType
{
float4 position : POSITION;
float2 tex : TEXCOORD0;
float3 normal : NORMAL;
};

struct PixelInputType
{
float4 position : SV_POSITION;
float2 tex : TEXCOORD0;
float3 normal : NORMAL;
};

PixelInputType LightVertexShader(VertexInputType input)
{
PixelInputType output;


// Change the position vector to be 4 units for proper matrix calculations.
input.position.w = 1.0f;

// Calculate the position of the vertex against the world, view, and projection matrices.
output.position = mul(input.position, worldMatrix);
output.position = mul(output.position, viewMatrix);
output.position = mul(output.position, projectionMatrix);

// Store the texture coordinates for the pixel shader.
output.tex = input.tex;
// Calculate the normal vector against the world matrix only.
output.normal = mul(input.normal, (float3x3)worldMatrix);

// Normalize the normal vector.
output.normal = normalize(output.normal);

return output;
}

Pixel Shader:

Texture2D shaderTexture;
SamplerState SampleType;

cbuffer LightBuffer
{   
float4 ambientColor;
float4 diffuseColor;
float3 lightDirection;
float padding;
};

struct PixelInputType
{
float4 position : SV_POSITION;
float2 tex : TEXCOORD0;
float3 normal : NORMAL;
};

float4 LightPixelShader(PixelInputType input) : SV_TARGET
{
float4 textureColor;
float3 lightDir;
float lightIntensity;
float4 color;

// Sample the pixel color from the texture using the sampler at this texture coordinate location.
textureColor = shaderTexture.Sample(SampleType, input.tex);

 // Set the default output color to the ambient light value for all pixels.
color = ambientColor;

// Invert the light direction for calculations.
lightDir = -lightDirection;

// Calculate the amount of light on this pixel.
lightIntensity = saturate(dot(input.normal, lightDir));

if(lightIntensity > 0.0f)
{
    // Determine the final diffuse color based on the diffuse color and the amount of light intensity.
    color += (diffuseColor * lightIntensity);
}

// Saturate the final light color.
color = saturate(color);

// Multiply the texture pixel and the final diffuse color to get the final pixel color result.
color = color * textureColor;

return color;
}