Hi,
When reading Frank Luna's book Introduction to 3D Game Programming with DX11, chapter 10 stenciling, the author made a demo to achieve mirror reflection effect. He made tranformation matrix and transform directional lights as following:
// Build reflection matrix to reflect the skull.
XMVECTOR mirrorPlane = XMVectorSet(0.0f, 0.0f, 1.0f, 0.0f); // xy plane
XMMATRIX R = XMMatrixReflect(mirrorPlane);
XMMATRIX world = XMLoadFloat4x4(&mSkullWorld) * R;
…/
/ Reflect the light source as well.
// Cache the old light directions, and reflect the light directions.
XMFLOAT3 oldLightDirections[3];
for(int i = 0; i < 3; ++i)
{
oldLightDirections = mDirLights.Direction;
XMVECTOR lightDir = XMLoadFloat3(&mDirLights.Direction);
XMVECTOR reflectedLightDir = XMVector3TransformNormal(lightDir, R);
XMStoreFloat3(&mDirLights.Direction, reflectedLightDir);
}But I think the direction of a light source is no more than a vector, not a normal. Why did the author use XMVector3TransformNormal to flip the lights? Thanks!
