I am following tutorials to implement directional light in directx, the diffuse part is as below

diffuse = float4(0.0f, 0.0f, 0.0f, 0.0f);
float diffuseFactor = dot(lightVec, normal);
diffuse = saturate(diffuseFactor * mat.Diffuse * L.Diffuse);

what confused me is the result of diffuse.

mat.Diffuse * L.Diffuse should be a float4, how could it be saved to "diffuse", a float type variable.

the same question to the ambient part

ambient = float4(0.0f, 0.0f, 0.0f, 0.0f);
ambient = mat.Ambient * L.Ambient;

both mat.Ambient and L.Ambient are float4 types, after the * operation, it should be a float type.

I find materials on the internet and found there are only two multiply operations of vectors,dot product and cross product, so why the code mentioned above still use *, but not dot function?

float4 a, b;
float4 c = a*b; //c = (a.x*b.x,a.y*b.y,a.z*b.z, a.w*b.w)

float a;
float4 b;
float4 c = a*b; //c = (a*b.x,a*b.y,a*b.z,a*b.w)

I am following tutorials to implement directional light in directx, the diffuse part is as below

diffuse = float4(0.0f, 0.0f, 0.0f, 0.0f);
float diffuseFactor = dot(lightVec, normal);
diffuse = saturate(diffuseFactor * mat.Diffuse * L.Diffuse);

what confused me is the result of diffuse.
mat.Diffuse * L.Diffuse should be a float4, how could it be saved to "diffuse", a float type variable.

the same question to the ambient part

ambient = float4(0.0f, 0.0f, 0.0f, 0.0f);
ambient = mat.Ambient * L.Ambient;

both mat.Ambient and L.Ambient are float4 types, after the * operation, it should be a float type.

I find materials on the internet and found there are only two multiply operations of vectors,dot product and cross product, so why the code mentioned above still use *, but not dot function?

That all looks fine, assuming diffuse and ambient are float4's, which they almost certainly should be if you want lights that aren't just white.

That all looks fine, assuming diffuse and ambient are float4's, which they almost certainly should be if you want lights that aren't just white.

Diffuse and ambient should be float3. There is no sense of calculating light value for alpha channel. It's just wasteful.

Thank you all, I have mistaken here

diffuse = float4(0.0f, 0.0f, 0.0f, 0.0f);
float diffuseFactor = dot(lightVec, normal);
diffuse = saturate(diffuseFactor * mat.Diffuse * L.Diffuse);

the correct one should be

diffuse = float4(0.0f, 0.0f, 0.0f, 0.0f);
float diffuseFactor = saturate(dot(lightVec, normal));
diffuse = diffuseFactor * mat.Diffuse * L.Diffuse;