Need help drawing light though the vexter shader

Need help drawing light though the vexter shader

I need some help with "drawing" out specular light thought the vexter
shader instead of the pixel shader , since my teacher want to prove a
point that it wont work properly.. I have tried to solve it myself , but I
can't mange to solve it..
The original code :
struct Light
{
float3 pos;
float range;
float3 dir;
float cone;
float3 att;
float4 ambient;
float4 diffuse;
};
cbuffer cbPerFrame
{
Light light;
};
cbuffer cbPerObject
{
float4x4 WVP;
float4x4 World;
};
Texture2D ObjTexture;
SamplerState ObjSamplerState;
struct VS_OUTPUT
{
float4 Pos : SV_POSITION;
float4 worldPos : POSITION;
float2 TexCoord : TEXCOORD;
float3 normal : NORMAL;
};
VS_OUTPUT VS(float4 inPos : POSITION, float2 inTexCoord : TEXCOORD, float3
normal : NORMAL)
{
VS_OUTPUT output;
output.Pos = mul(inPos, WVP);
output.worldPos = mul(inPos, World);
output.normal = mul(normal, World);
output.TexCoord = inTexCoord;
return output;
}
float4 PS(VS_OUTPUT input) : SV_TARGET
{
input.normal = normalize(input.normal);
float4 diffuse = ObjTexture.Sample( ObjSamplerState, input.TexCoord );
float3 finalColor = float3(0.0f, 0.0f, 0.0f);
//Create the vector between light position and pixels position
float3 lightToPixelVec = light.pos - input.worldPos;
//Find the distance between the light pos and pixel pos
float d = length(lightToPixelVec);
//Add the ambient light
float3 finalAmbient = diffuse * light.ambient;
//If pixel is too far, return pixel color with ambient light
if( d > light.range )
return float4(finalAmbient, diffuse.a);
//Turn lightToPixelVec into a unit length vector describing
//the pixels direction from the lights position
lightToPixelVec /= d;
//Calculate how much light the pixel gets by the angle
//in which the light strikes the pixels surface
float howMuchLight = dot(lightToPixelVec, input.normal);
//If light is striking the front side of the pixel
if( howMuchLight > 0.0f )
{
//Add light to the finalColor of the pixel
finalColor += diffuse * light.diffuse;
//Calculate Light's Distance Falloff factor
finalColor /= (light.att[0] + (light.att[1] * d)) + (light.att[2]
* (d*d));
//Calculate falloff from center to edge of pointlight cone
finalColor *= pow(max(dot(-lightToPixelVec, light.dir), 0.0f),
light.cone);
}
//make sure the values are between 1 and 0, and add the ambient
finalColor = saturate(finalColor + finalAmbient);
//Return Final Color
return float4(finalColor, diffuse.a);
}
float4 D2D_PS(VS_OUTPUT input) : SV_TARGET
{
float4 diffuse = ObjTexture.Sample( ObjSamplerState, input.TexCoord );
return diffuse;
}