Deferred Rendering - Practical Rendering and Computation with Direct3D 11 - page 521

// Clamp the rectangle to the screen extents
rectTopCS = Clamp( rectTopCS, -1.0f, 1.0f );
rectBottomCS = Clamp( rectBottomCS, -l.0f, l.0f );
rectLeftCS = Clamp( rectLeftCS, -l.0f, l.ef );
rectRightCS = Clamp( rectRightCS, -l.0f, 1.0f );
// Now we convert to screen coordinates by applying the
// viewport transform
float rectTopSS = rectTopCS * 0.5f + 0.5f;
float rectBottomSS = rectBottomCS * 0.5f + 0.5f;
float rectLeftSS = rectLeftCS * 0.5f + 0.5f;
float rectRightSS = rectRightCS * 0.5f + 0.5f;
rectTopSS = 1.0f - rectTopSS;
rectBottomSS = l.0f - rectBottomSS;
rectTopSS *= m_uVPHeight;
rectBottomSS *= m_uVPHeight;
rectLeftSS *= m_uVPWidth;
rectRightSS *= m_uVPWidth;
// Final step is to convert to integers and fill out the
// D3D11_RECT structure
D3D11_RECT rect;
rect.left = static_cast<LONG>( rectLeftSS );
rect. right = static_cast<LON6>( rectRightSS );
rect.top = static_cast<LONG>( rectTopSS );
rect.bottom = static_cast<LONG>( rectBottomSS );
// Clamp to the viewport size
rect.left = max( rect.left, 0 );
rect. top = max( rect.top, 0 );
rect.right = min( rect. right, static_cast<LONG>( m_uVPWidth ) );
rect.bottom = min( rect.bottom, static_cast<LONG>( m_uVPHeight ) );
return rect;
}
Listing 11.14. C++ code for fitting scissor rectangle to a point light.
For a spot light, we can use the same process of fitting a bounding sphere and de-
termining the screen-space extents. The code in Listing 11.14 will work for a spot light
without any modifications, since the resulting bounding sphere will completely encompass
the conical area of effect, regardless of the light's orientation and angular attenuation pa-
rameters. If necessary, the angular attenuation factors can be used to fit a bounding cone to
the light, to which a tighter bounding sphere can be fit.
An alternative to this approach is to approximate the light's bounding cone using a
mesh of vertices, and then calculate the bounding box, based on the vertices' projected
positions in screen space. This requires more calculations at runtime, but it can potentially
result in a tighter fit than using a bounding sphere.