| 575 |
|
short lookups. Setting this radius too large, on the other hand, may |
| 576 |
|
degrade performance. |
| 577 |
|
.TP |
| 578 |
+ |
.BI -ac " pagesize" |
| 579 |
+ |
Set the photon cache page size when using out-of-core photon mapping. The |
| 580 |
+ |
photon cache reduces disk I/O incurred by on-demand loading (paging) of |
| 581 |
+ |
photons, and thus increases performance. This |
| 582 |
+ |
is expressed as a (float) multiple of the density estimate bandwidth |
| 583 |
+ |
specified with |
| 584 |
+ |
.I \-ap |
| 585 |
+ |
under the assumption that photon lookups are local to a cache page. Cache |
| 586 |
+ |
performance is sensitive to this parameter: larger pagesizes will reduce the |
| 587 |
+ |
paging frequency at the expense of higher latency when paging does occur. |
| 588 |
+ |
Sensible values are in the range 4 (default) to 16. |
| 589 |
+ |
.TP |
| 590 |
+ |
.BI -aC " cachesize" |
| 591 |
+ |
Set the total number of photons cached when using out-of-core photon |
| 592 |
+ |
mapping, taking into account the pagesize specified by |
| 593 |
+ |
.I \-ac. |
| 594 |
+ |
Note that this is approximate as the number of cache pages is rounded to |
| 595 |
+ |
the nearest prime. This allows adapting the cache to the available physical |
| 596 |
+ |
memory. In conjunction with the |
| 597 |
+ |
.I \-n |
| 598 |
+ |
option, this is the cache size |
| 599 |
+ |
.I per parallel process. |
| 600 |
+ |
Cache performance is less sensitive to this parameter, |
| 601 |
+ |
and reasonable performance can obtained with as few as 10k photons. The |
| 602 |
+ |
default is 1M. This option recognises multiplier suffixes (k = 1e3, M = |
| 603 |
+ |
1e6), both in upper and lower case. |
| 604 |
+ |
.TP |
| 605 |
|
.BI -me " rext gext bext" |
| 606 |
|
Set the global medium extinction coefficient to the indicated color, |
| 607 |
|
in units of 1/distance (distance in world coordinates). |
