Graphics Reference
In-Depth Information
// Read roughness from a render target and convert to a BRDF
// specular power .
float
specularPower
=
roughnessToSpecularPower
(
roughness
);
// Depending on what BRDF used , convert to cone angle . Cone
// angle is maximum extent of the specular lobe aperture .
float
coneTheta
=
specularPowerToConeAngle
(
specularPower
);
// Cone
trace using an isosceles triangle to approximate a cone
// in screen space
for
(
int
i
=0;
i
<
7; ++
i
)
{
−
// Intersection length is the adjacent side , get the opposite
// side using trigonometry
float
oppositeLength
=
isoscelesTriangleOpposite
(
adjacentLength
,
coneTheta
);
// Calculate in
−
radius of the isosceles triangle now
float
incircleSize
=
isoscelesTriangleInradius
(
adjacentLength
,
oppositeLength
);
// Get the sample position in screen space
float2
samplePos
=
screenPos
.
xy
+
adjacentUnit
(
adjacentLength
−
incircleSize
);
// Convert the in
−
radius into screen size (960x540) and then
// check what power N we have to raise 2 to reach it .
// That power N becomes our mip level to sample from.
float
mipChannel
=
log2
(
incircleSize
max
(
screenSize
.
x
,
screenSize
.
y
));
// Read color and accumulate it using trilinear filtering
// (blending in xy and mip direction) and weight it .
// Uses pre
−
convolved image and pre−i
−
integrated transparency
// buffer and Hi
Z buffer . It checks if cone sphere is below,
// in between , or above the Hi
−
Z minimum and maxamimum and
// weights it together with transparency.
// Visibility is accumulated in the alpha channel .
totalColor
+=
coneSampleWeightedColor
(
samplePos
,
mipChannel
−
←
);
if
(
totalColor
.
a
>
1.0
f
)
break
;
// Calculate next smaller triangle that approximates the cone
// in screen space .
adjacentLength
=
isoscelesTriangleNextAdjacent
(
adjacentLength
,
incircleSize
);
}
Listing 4.7.
Again the full implementation of some of the functions is not shown
because of code length. The demo code available online has the full implementation;
the demo also comes with alternative toggle-able code for accumulating the colors such
as basic averaging, distance-based weighting, and hierarchical pre-integrated visibility
buffer weighting.
