OpenGL Insights

284 III Bending the Pipeline

11

11 133

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1

2

(a)

15 15 16 17 19 19 19 19

6 7 8 11 14 15 15 15

11235666

00011111

(b)

Figure 20.5. An example of (a) counts and (b) offsets for three triangles.

In step 3, offsets are computed, applying the parallel prefix sum algorithm [Lad-

ner and Fischer 80] to the count data. The offsets are computed in place, overwriting

the counts since the counts can be recalculated as the difference between consecutive

offset values. This algorithm is visualized in Figure 20.4(b), and an example of the

final offset table is shown in Figure 20.5(b). For simplicity, the input data for the

parallel prefix sums is increased to the next power ...