Redshift The Brute-Force GI Engine

How It Works工作原理

The Brute-Force GI Engine is the most basic GI Engine. It doesn』t attempt to interpolate any results and, as such, is very accurate but also the slowest.

Brute-Force GI Engine是最基本的GI引擎，由於不進行任何的差值運算，因此Brute-Force引擎計算非常準確，但也是最慢的方式。

Brute-Force can be selected as a primary or secondary GI engine. It works by simply shooting rays as shown below.

Brute-Force可以選擇作為Primary或者Secondary GI引擎。它的工作方式僅僅就是發射採樣射線而已，如下所示：

Zero GI Bounces. Camera shoots a ray and hits wall (point 「A」). The primary GI engine is used and shoots another ray of which is shown in red. This way, direct lighting (black dashed line) on point 「B」 affects point 「A」.

第0次GI反彈。攝像機發射出一條採樣射線，到達牆壁上A點。Primary GI引擎啟動，發射出另一條採樣射線（圖中以紅色顯示）。這樣一來，接受直接照明（黑色虛線）的B點就影響A點。

One GI Bounce. The processing now goes a bit further. Point 「B」 uses the secondary GI engine to gather illumination from the sphere by shooting a single ray (shown in blue). This way, the direct lighting (black dashed line) of points 「B」 and 「C」 affects point 「A」.

第1 次GI反彈。渲染繼續進行。B點採用Secondary GI引擎發射採樣射線（以藍色顯示）收集來自球體的光影信息。這樣一來，被直接照亮的B點和C點（黑色虛線）就會共同影響A點。

Pros優點

1、Very accurate非常精準

2、No flickering in animations沒有動畫閃爍問題

3、It』s easy as it only has one setting to tweak (「Num Rays」)沒有什麼要調節的參數。

4、Does not require any storage so the final image resolution and scene detail does not matte。不需要任何預先存儲信息，所以最終圖像的解析度和場景細節都不會在渲染工作中對內存有更多額外的需求。

Cons缺點

1、It』s the slowest technique. But due to Redshift』s speed, it』s more practical compared to other renderers.速度最慢的方式。但由於RedShift的計算速度會比其它渲染器快一些。

2、Unless many rays are shot per pixel, it can produce grainy images – especially in difficult lighting situations除非在每個像素都 需要發射大量採樣射線，否則會產生顆粒感的圖像 尤其是在光線不好的情況下。

3、增加渲染解析度會線性的增加渲染時間。

Settings設置

Num Rays採樣射線設置

With Brute Force GI, each pixel on the screen has its GI computed by shooting out a number of rays. The more rays are shot, the cleaner (less 「grain」) the result but the longer the computation time. Scenes that have few small bright light sources might need many rays to produce grain-free results.

運用Brute Force GI，屏幕上的每個像素都是通過發射大批量採樣射線來計算GI效果。發射越多，渲染結果就越乾淨（更少的顆粒感），同時這也需要更長的計算時間。只有幾個小亮光源的場景可能需要非常多的光線來產生無顆粒的渲染畫面。

How To Use 如何使用

Num Rays採樣射線數量

Below we show the effect of 「Num Rays」. The images are pretty self-explanatory.

下面展示的是「Num Rays」的作用。原理顯而易見。

「Num Rays」 set to 16. The result is grainy.

「Num Rays」設置為16，畫面中充滿了噪點。

Now using 512 rays, which produces a smoother result.

「Num Rays」設置增加到512畫面質量細膩了很多。