GPU PRO 3

3. Volumetric Real-Time Water and Foam Rendering 129

3.3.5 Volumetric Compositing

The difference between the usual compositing of layers and volumetric composit-

ing is that we take the thickness of each layer into account to attenuate a viewing

ray. Compositing along a viewing ray back to front, we have (see Figure 3.2):

C

wb

= lerp(c

fluid

, C

background

, e

−T

wb

)

,

C

foam

= lerp(c

fb

, c

ff

, e

−T

f f

),

C

f

= lerp(C

foam

, C

wb

, e

−T

f

),

C

wf

= lerp(c

fluid

, C

f

, e

−T

wf

),

where c

fluid

is the water color and c

ff

and c

fb

are two user-defined colors that

are blended together to create more freedom in designing the look of the foam.

After attenuation, we calculate highlights at the front ...