GPGPU Programming for Games and Science

GPU Computing 143

G

y

-1

N

y

=G

y

*T

y

threads

0

g

y

N

x

=G

x

*T

x

threads

0

g

x

G

x

-1

T

y

-1

0

t

y

0

t

x

T

x

-1

(T

x

*g

x

+t

x

, T

y

*g

y

+t

y

)

Base index of upper left

corner is (N

x

*g

x

, N

y

*g

y

)

FIGURE 4.8: An illustration of Equation (4.22) that relates the dispatch

thread ID to the group ID and the group thread ID.

t as an int2 for convenience. Notice that output is a 2D texture. This compute

shader has no need for texture sampling, so we can look up the texture values

directly without sampling. The

operator[] provides the direct lookup and it

expects a 2-tuple for the index. Because

t is already a 2-tuple, I can use it as

is. However, if I had declared

int3 t, then I would need to perform the lo ...