//-----------------------------------------------------------------------
// Pixel shader function (DIRECTIONAL LIGHT)
//-----------------------------------------------------------------------
float4 PS( VS_OUTPUT IN ) : COLOR
{
    float3 viewDir = cameraPos - IN.worldPos;
    float3 lightDir = -lightDirection;
    float3 halfVector = normalize(normalize(lightDir) + normalize(viewDir));

    float3 n = normalize(IN.Normal);
    float3 h = normalize(halfVector);
    float3 l = normalize(lightDir);
    
    float nDotL = saturate(dot(n, l));
    float nDotH = saturate(dot(n, h));
    float power = (nDotL == 0.0f) ? 0.0f : pow(nDotH, materialPower);
    
    float4 FinalDiffuse = materialDiffuse * lightDiffuse;
    float4 FinalSpecular = materialSpecular * lightSpecular;

    float4 color = (materialAmbient + globalAmbient) +
                   (FinalDiffuse * nDotL) + (FinalSpecular * power);
    return color * tex2D(colorMap, IN.UV);
}

Here is a part of the C++ code:

// Light
float lightDiffuse[4] = {1.0f, 1.0f, 1.0f, 0.01f};
float lightSpecular[4] = {0.5f, 0.5f, 0.5f, 0.5f};
pEffect->SetValue("lightDiffuse", &lightDiffuse, sizeof(lightDiffuse));
pEffect->SetValue("lightSpecular", &lightSpecular, sizeof(lightSpecular));

// Material
float materialDiffuse[4] = {1.0f, 1.0f, 1.0f, 1.0f};
float materialAmbient[4] = {0.15f, 0.15f, 0.15f, 1.0f};
float materialSpecular[4] = {1.0f, 1.0f, 1.0f, 1.0f};
float materialPower = 10.0f;

float gAmbient[4] = { 1.0f, 1.0f, 1.0f, 1.0f };
pEffect->SetValue("globalAmbient", &gAmbient, sizeof(gAmbient));

D3DXVECTOR3 lightDirection(0.0f, 10.0f, 1.0f);
pEffect->SetValue("lightDirection", &lightDirection, sizeof(D3DXVECTOR3));
pEffect->SetValue("cameraPos", &getCameraPosition(), sizeof(D3DXVECTOR3));

pEffect->SetTexture("colorMapTexture", texture);

VS_OUTPUT VS( VS_INPUT IN )
{
    VS_OUTPUT Out;
    Out = (VS_OUTPUT)0;
    float4x4 WVP = mul(World, mul(View, Projection));
    Out.Pos = mul(float4(IN.Pos, 1.0f), WVP);
    Out.UV = IN.UV;
    Out.Normal = mul(IN.Normal, (float3x3)World);
    Out.worldPos = mul(float4(IN.Pos, 1.0f), World).xyz;
    return Out;
}