float4x4 invProj;
float4x4 invView;

float3 lightPos;
float3 lightColor;
float lightIntensity;
float3 cameraPos;

void VS_light(in  float4 inPosition            : POSITION,
              out float4 outPosition           : POSITION,
              out float4 outWorldPosition      : TEXCOORD0) {
    outPosition = inPosition;
    outWorldPosition = mul(invView, mul(invProj, inPosition));
}

void PS_light(in  float4 inWorldPosition       : TEXCOORD0,
              out float4 outColor              : COLOR)
{
    float4 value;
    outColor = float4(0, 0, 0, 0);
    float3 position = inWorldPosition.xyz;
    float distance = length(lightPos - position);
    const float stepSize = distance / 250.0;
    const float3 rayStep = normalize(position - cameraPos) * stepSize;

    [unroll(2)]
    for (int i = 0; i < 250; i++) {
        float lightAttenuation = 1 / pow(distance, 3);
        float shadow = 1.0;//shadow(position);
        float opacity = 1.0;
        value.rgb = (1.0 - outColor.a) * (lightColor * lightIntensity * lightAttenuation * shadow);
        value.a = (1.0 - outColor.a) * opacity;
        outColor += value;
        position += rayStep;
        distance -= stepSize;
    }
}

technique light
{
    pass
    {
        VertexShader = compile vs_2_0 VS_light();
        PixelShader = compile ps_2_0 PS_light();
    }
}