Mathematical Topics from 3D Graphics - 3D Math Primer for Graphics and Game Development - page 349

particular location. (Later, we see how those intuitive terms in quotes are
a bit too vague for rendering purposes.) Compared to a forward renderer,
a deferred renderer follows our two-step rendering algorithm a bit more lit-
erally. First we “render” the scene into the G-buffer, essentially performing
only visibility determination—fetching the material properties of the point
that is “seen” by each pixel but not yet performing lighting calculations.
The second pass actually performs the lighting calculations. Listing 10.3
explains deferred rendering in pseudocode.

/ / C l e a r t h e geometry and depth b u f f e r s

c l e a r G e o m e t r y B u f f e r ( ) ;
f i l l D e p t h B u f f e r ( i n f i n i t y ) ;

/ / R a s t e r i z e a l l p r i m i t i v e s i n t o t h e G − b u f f e r

f o r ( each g e o m e t r i c p r i m i t i v e ) {

f o r ( each p i x e l x , y i n t h e p r o j e c t i o n o f t h e p r i m i t i v e ) {

/ / T e s t t h e depth b u f f e r , t o s e e i f a c l o s e r p i x e l has

/ / a l r e a d y been w r i t t e n .

f l o a t primDepth = g e t D e p t h O f P r i m i t i v e A t P i x e l ( x , y ) ;

i f ( primDepth > r e a d D e p t h B u f f e r ( x , y ) ) {

/ / P i x e l o f t h i s p r i m i t i v e i s obscured , d i s c a r d i t

c o n t i n u e ;

}

/ / F e t c h i n f o r m a t i o n needed f o r s h a d i n g i n t h e n e x t p a s s .

M a t e r i a l I n f o m t l I n f o ;
V e c t o r 3 pos , n o r m a l ;
g e t P r i m i t i v e S h a d i n g I n f o ( m t l I n f o , pos , n o r m a l ) ;

/ / Save i t o f f i n t o t h e G − b u f f e r and depth b u f f e r

w r i t e G e o m e t r y B u f f e r ( x , y , m t l I n f o , pos , n o r m a l ) ;

w r i t e D e p t h B u f f e r ( x , y , primDepth ) ;

}

}

/ / Now p e r f o r m s h a d i n g i n a 2nd pass , i n s c r e e n space

f o r ( each x , y s c r e e n p i x e l ) {

i f ( r e a d D e p t h B u f f e r ( x , y ) == i n f i n i t y ) {

/ / No geometry h e r e . J u s t w r i t e a background c o l o r

w r i t e F r a m e B u f f e r ( x , y , b a c k g r o u n d C o l o r ) ;

} {

e l s e

/ / F e t c h s h a d i n g i n f o back from t h e geometry b u f f e r

M a t e r i a l I n f o m t l I n f o ;
V e c t o r 3 pos , n o r m a l ;
r e a d G e o m e t r y B u f f e r ( x , y ,

m t l I n f o , pos , n o r m a l ) ;

/ / Shade t h e p o i n t

C o l o r c = s h a d e P o i n t ( pos , normal , m t l I n f o ) ;

/ / P u t i t i n t o t h e f ra m e b u f f e r

w r i t e F r a m e B u f f e r ( x , y , c ) ;

}

}
Listing 10.3
Pseudocode for deferred rendering using the depth buffer