rotate object but keeping lighting fixed DirectX? - c++

Question

i am using directx11 , and i create light source ( parallel light source )and scene ( loaded from obj file ) , and every thing look correct but when i rotate some object in the scene , my light rotate too with the object , and i don't wont to rotate the light and keep it fixed .
i try to fix the problem by do something like this , but i fail :
XMMATRIX light_rotat = XMMatrixIdentity()
/*render the light*/
XMMATRIX light_rotat = XMMatrixRotationY(timeGetTime()/3500.0f);
/* render scene */
/* the hlsl code */
cbuffer LIGHT
{
float4 light_color ;
float3 Direction ;
float3 Position ;
float3 attribute ;
float Power ;
float range ;
float spotpower ;
};
cbuffer CAMERA
{
float4x4 view ;
float4x4 world ;
float4x4 proj ;
};
cbuffer local
{
float3 eye;
float4x4 localworld ;
};
Texture2D texture_obj ;
SamplerState Texture_sampler ;
/* diffuse texture */
float4 Get_Texture (float2 uv )
{
return texture_obj.Sample (Texture_sampler , uv );
}
/* light calc */
float4 Parrallel (float3 eye ,float3 Position ,float3 Normal , MTRL mtrl )
{
float3 lightvec = normalize(-Direction) ;
float4 LitColor = float4(0.0f , 0.0f ,0.0f ,0.0f );
float diff_factor = dot(lightvec , Normal );
float4 diff = light_color * mtrl.Diffuse_Mtrl ;
if (diff_factor > 0.0f )
{
float4 amb = light_color * mtrl.Ambient_Mtrl ;
float3 view = normalize(eye - Position) ;
float3 rf = normalize(reflect (Direction , Normal )) ;
float4 Spec_Fac = pow ( max ( dot (rf , view ) , 0.0f ) , max (1.0f ,Power ));
float4 Spec = light_color * mtrl.Specular_Mtrl ;
LitColor += ( diff *diff_factor) + (Spec_Fac*Spec) + (amb*diff_factor) ;
}
return LitColor ;
}
struct VS_INPUT
{
float4 Pos :POSITION ;
float3 Normal : NORMAL0 ;
float2 UV : TEXCOORD0 ;
};
struct VS_OUT
{
float4 Pos :SV_Position ;
float4 Posw : POSITION ;
float4 Normal : TEXCOORD1 ;
float2 UV : TEXCOORD0 ;
};
VS_OUT VS (VS_INPUT input)
{
VS_OUT v ;
v.Pos = mul ( input.Pos , localworld );
v.Pos = mul (v.Pos , world );
v.Pos = mul (v.Pos , view );
v.Pos = mul (v.Pos , proj );
v.Posw = mul ( input.Pos, localworld );
v.UV = input.UV ;
v.Normal = mul (float4(input.Normal , 0.0f) ,world );
return v ;
}
float4 PS (VS_OUT ps):SV_Target
{
MTRL y ;
y.Diffuse_Mtrl = Get_Texture (ps.UV);
y.Ambient_Mtrl = y.Diffuse_Mtrl /8 ;
y.Specular_Mtrl = float4 ( 0.5f , 0.5f , 0.5f , 0.0f );
float4 licolor = Parrallel ( eye , (float3)ps.Posw , (float3)ps.Normal ,y ) ;
return licolor ;
}
technique11 tech2
{
pass P0
{
SetVertexShader( CompileShader( vs_5_0, VS() ) );
SetPixelShader( CompileShader( ps_5_0, PS() ) );
}
}
this is the render loop
Device->Draw(Color);
t.localworld = ::XMMatrixTranspose ( XMMatrixRotationY ( timeGetTime() /3000.0f ) );
t.eye = XMFLOAT3( 0.0f, 10.0f, -30.0f );
local->UpdateSubresource (My_Buffer , 0 , NULL ,0, 0 , &t );
ID3DX11EffectConstantBuffer *cm = effect->Get_Effect()->GetConstantBufferByName ( "local");
cm->SetConstantBuffer ( Local->Get_Buffer());
effect->Apply(Flags , Context);
mesh->draw();
Device->EndDraw();
any help ?

Answer 1

Ok, the 'localworld' matrix should be the key here, what you need to do is create a rotation matrix Y , and multiply the localworld variable, with this rotation matrix, before you write the localworld variable to HLSL in your render loop. That should rotate you vertices only, and your light should stay static.