Redshift The Irradiance Point Cloud GI Engine輻射點雲GI

How It Works工作原理

When multiple GI bounces are needed, each ray has to bounce a few times around until it reaches a light. Because the ray bouncing happens randomly finding lighting, in some ways, is left to chance. Using more rays improves these chances, which is why increasing the ray counts always produces cleaner results.

如果需要多次GI反彈，則每條射線在反彈很多次後才抵達光源。由於射線反彈尋找光源是隨機的，因而遇到光源某種程度上是概率事件。所以越多的射線意味著得到越乾淨的結果。

The Irradiance Point Cloud attempts to improve the situation by computing a coarse GI approximation on random points around the scene. In some ways it』s similar to the Irradiance Cache except:

Irradiance Point Cloud通過一種在隨機點周圍粗略的GI近似來提供渲染質量，它的過程與Irradiance Cache很近似，除了以下不同：

It creates points in places that might not be visible to the camera. This necessary because multiple GI ray bounces will very often land on out-of-camera-frustum locations.

它生成信息點的位置有可能在攝像機之外。這是有必要的。因為多次GI射線的反彈很可能觸及攝像機視野之外的區域。

The points don』t care too much about creases and detail. This is done to conserve memory and improve computation time.

這些信息點並不明顯反映出縫隙和細節。這麼做的目的是節省內存，縮短渲染時間。

The figures below show how the Irradiance Point Cloud works

下面這幅圖展示Irradiance Point Cloud是如何工作的：

During the irradiance point cloud computation pass, rays are shot from the camera, create points on intersections and are bounced around. That creates a 『blanket』 of points around the scene. A coarse GI solution is incrementally computed on each of these points.

在Irradiance Point Cloud計算過程中，射線從相機射出，遇到物體表面後形成點，並向四周反彈，之後形成一層覆蓋場景的點。通過對這些點遞進式計算，可以得到一個初略的GI計算結果。

During Irradiance Caching or Brute-Force primary GI, these points are used to compute a smoother GI result. Here, the lighting of an irradiance cache point (shown in white) is computed using the irradiance point cloud.

當使用Irradiance Cache或者Brute Force作為Primary GI時，通過這些信息點，能渲染得到一個更為平滑的結果。下圖Irradiance Cache點（白色點）就是使用Irradiance Point Cloud（輻射點雲信息）來計算的。

Looking at the second figure, if we didn』t have the point cloud enabled, the irradiance cache point (white point) would have to shoot the rays shown as dashed arrows and then bounce those rays off the wall. Finding lighting this way would be hard. Using the irradiance point cloud, instead, each of these dashed array rays gets back lighting that is of higher quality.

看第二張圖，如果我們不使用點雲，Irradiance Cache點（白色點）就必須再發射射線（虛線箭頭所示）到周圍場景，再從牆壁上反彈這些射線。以這種方式尋找光源計算很大。藉助於Irradiance Point Cloud（輻射點雲），得到的光源信息質量更高。

Even though each one of these points contains a coarse lighting solution (meaning it can be fairly noisy), that is often not a big issue with secondary GI lighting. The same applies to the Photon Map when it』s used as a secondary GI engine: it might be a bit splotchy, but the final result can still be clean.

儘管每個信息點包含的信息只是粗略近似，但用作Second GI還是足夠了。同樣當Secondary GI選擇Photo Mapping時，也是類似的情況，儘管有斑塊，但最終呈現出來的結果仍然會是乾淨的。

Later in this document there are pictures that shown the kind of visual benefit you can expect from the Irradiance Point Cloud.

下面展示的是使用Irradiance Point Cloud的幾個特點。

Pros優點：

Helps make Brute-Force and Irradiance Caching faster and cleaner 幫助Brute Force 和Irradiance Cache渲染更快更乾淨。

Certain very difficult lighting scenarios can only be rendered with this technique! (i.e. they would take an extremely long time with purely brute force techniques)適合燈光對比度較大的場景（如果用Brute Force渲染會花費大量的時間。）

Cons缺點：

Requires some storage (but, typically, not much) 佔用存儲空間（但不會很多）

There are a few settings to tweak so a bit of experimentation is required.需要調節一些參數。

Only provides a benefit when multiple bounces are needed, if the scene contains lots of lights or when the lighting conditions are difficult只有在多重反彈和極端的燈光配置中才體現出優勢。否則，用Brute Force能達到同樣的效果，且不需要額外的預測計算進程和存儲開銷。

Settings設置

Mode/Filename 模式 文件名

When 「Mode」 is set to 「Rebuild (don』t save)」, Redshift will compute a new irradiance point cloud from scratch (for each frame) but will not save it to disk. The frame will be rendered to completion.

當模式設置為Rebuild (don』t save) （重建 不保存）時，Redshift會計算新的Irradiance Point Cloud但不會存儲到硬碟。這一幀將被完整渲染出來。

When 「Mode」 is set to 「Rebuild (prepass only)」, Redshift will compute a new irradiance point cloud from scratch (for each frame) and will save it to the user-specified file. The final rendering pass will be skipped.

當模式設置為Rebuild（Prepass only）（重建 預計算）時，Redshift會計算新的Irradiance Point Cloud並且存儲到硬碟。最終渲染過程會被跳過。

When 「Mode」 is set to 「Rebuild」, Redshift will compute a new irradiance point cloud from scratch (for each frame) and will save it to the user-specified file. The frame will be rendered to completion.

當模式設置為Rebuild（重建）時，Redshift會計算新的Irradiance Point Cloud並且存儲到用戶指定文件內。這一幀將被完全渲染出來。

When 「Mode」 is set to 「Load」, the computation stage is skipped and the data is loaded from the user-specified file. The frame will be rendered to completion.

當模式設置為Mode（載入）時，Redshift會從用戶指定文件載入之前存儲的點雲數據。這一幀將被完全渲染出來。

Number of frames to blend融合幀數

The 「Number of frames to blend」 parameter is only enabled when the 「Mode」 is set to 「Load」. It allows averaging the results of multiple irradiance point cloud files (one for each frame) together in order to improve any flickering effects that might be present because of insufficient quality settings and/or difficult lighting situations. Please refer tothis sectionbelow for more information on how to use the 「Rebuild (prepass)」 and 「Load」 modes. Since this mode has to do with loading and blending multiple frames before rendering, it』s only available for the 「Load」 mode and is grayed out for the 「Rebuild」 modes.

Number of frame to blend參數僅當模式為Load時起作用。它使得渲染器在渲染時先計算多個幀的點雲信息的平均值，再利用平均值來避免由於渲染質量開得不夠高和燈光條件很苛刻所造成的閃爍。使用Rebuild（Prepass）和Load模式的調節方法詳見下面的內容。由於該模式具有渲染之前做載入和緩存的混合工作。所以僅適用於載入模式。在重建模式下，顯示為灰色不可用。

Irradiance Point Cloud data is view-dependant which means that it has to be re-generated when either the camera or any objects move. It also has to be regenerated if lights change (position or intensity) and if materials are adjusted.

Irradiance Point Cloud信息是隨著視角變化和變化的。無論是物體移動還是視角運動，都需要重新計算。同樣改變燈光強度和位置以及改變材質，也一樣需要重新計算。

Show Calculation顯示計算過程

Due to the way the irradiance point cloud works, it can be very hard to directly visualize it, unfortunately. So what this option does is show the color results of the rays shot from the camera. For this reason, it looks like progressive rendering.

Irradiance Point Cloud的計算特點意味著它無法被直觀的觀察。這一選項能給用戶反饋一些來自攝像機射線生成的色彩斑點效果，功能上有些類似於漸進式渲染。

The overhead of this option can be significant on some very simple scenes so disabling 「Show Calculation」 can make the computation a bit faster.

對於特別簡單的場景，取消這一項能略微節省一點時間。

Screen Radius顯示尺度

Like mentioned above, the Irradiance Point Cloud algorithm stores points around the scene. It can』t storea point for each ray that was shot from the camera because doing so would generate an extremely large number of points for high-resolution images. Instead, it uses a screen-space metric to space out these points. So the 「Screen Radius」 parameter refers to pixels.

像上面所提到的，Irradiance Point Cloud 演算法存儲場景中信息點，如果渲染解析度很高，那它不會存儲所有從相機發出射線產生的信息點，那樣數據量會過大。取而代之，Irradiance Point Cloud使用Scene-Space Metric（顯示空間單位）來隔開這些點，因而Scene Radius 參數實際上單位是像素。

This parameter affects two things:這個參數影響兩點：

1、The used videocardmemory. Setting 「Screen Radius」 to larger values means that fewer points will be created and, therefore, less videocard memory will be used.

被使用的顯卡顯存。設置更大的Screen Radius意味著產生更少的點，以及更少的顯存佔用。

2、How often the results can be used by the primary GI engines. If the points are very far apart (because of a large screen radius), then the primary GI engines (Irradiance Cache, Brute-Force) will not use them as often (and depending on the 「Retrace Threshold」 parameter). So this can effect the performance of these two primary GI engines. Therefore, lower screen radius values can translate into better rendering performance.

結果能被Primary　GI引擎利用多少。如果信息點之間的距離很大Screen Radius參數控制，則PrimaryGI引擎（Irradiance Cache，Brute Force）會減少調用它們的次數（也受Retrace Threshold參數的影響）。因此這一參數會影響上面兩種 PrimaryGi引擎的效率。 也就是說Screen Radius越小，意味著更快的渲染速度。

Often times a setting of 8 or 16 will work fine. If you scene is of a high resolution (2K or larger) you can try larger values such as 32 or 64.

通常情況下8或16即可。如果你的場景解析度很高（2K或者更高）你可以試著增加到32或者64。

Note注意

If your videocard has enough VRAM (2GB or more), we strongly suggest using relatively low screen radius values, such as 8 for the performance reason explained above.

如果顯卡顯存足夠（2G以上）我們強烈建議使用較低的Screen Radius比如說8，來提升渲染速度。

Samples Per Pixel單個像素採樣

This parameter controls the quality of each point. In some ways, this works like 「Num Rays」 for Brute-Force or the Irradiance Cache, i.e. larger values produce smoother results. Scenes that are fairly well-lit (large light sources or several of them covering most surfaces) can use values such as 8 or 16. Harder lighting scenarios (small bright light sources or lighting coming through small openings) will need higher settings such as 32 or 64.

這個參數控制每個信息點的質量。類似於Brute Force或者Irradiance Cache中的Num Rays，數值越大，結果越平滑。如果場景光源條件比較好（大型光源或者多個光源覆蓋大部分區域）可以用8或者16。如果光源條件苛刻（小光源或者小窗口照射）則需要32或者64

The 「Screen Radius」 can also play a role in the final point quality. If you increase 「Screen Radius」 there are fewer points so each point will receive more rays and, hence, be smoother.

Screen Radius也在一定程度上影響最終像素點的質量。Screen Radius越大，產生的信息點越少，像素點就要依賴更多的採樣射線，因此渲染明結果也更平滑。

Filter Size過濾尺寸

As shown in the figures near the top of this document, the Irradiance Point Cloud is used by Brute-Force or the Irradiance Cache. When rays shot by Brute-Force or an Irradiance Cache point hit a surface, the closest Irradiaince Point Cloud points are found and used. The 「Filter Size」 controls how many of these 「closest points」 the algorithm should use.

如文檔最前面的圖所示，Irradiance Point Cloud是用來輔助Brute Force或者 Irradiance Cache的。當使用Brute Force或者Irradiance Cache演算法發射的採樣射線觸及物體表面時，最近處的Irradiance Point Cloud信息點會被使用。Filter Size決定演算法將使用多少最近處的Irradiance Point Cloud信息點。

Larger numbers will smooth out the points but will take longer to render. The default 2 value should work for most cases. We generally recommend smoothing out the Irradiance Point Cloud using more 「Samples Per Pixel」 instead of increasing 「Filter Size」.

數值越大，結果就越平滑。但渲染時間會加長。默認為2適用於絕大多數場景。要使結果平滑，通常建議優化增加Sample Per Pixel，而不是調整這個參數。

Retrace Threshold光線追蹤閾值

The Irradiance Point Cloud is constructed without too much care about scene detail (creases, corners, etc). This is done to conserve memory. Not doing so would mean creating a very large number of points around corners – like the Irradiance Cache has to do.

Irradiance Point Cloud並不負責處理場景中的細節，用它只能為了節省內存。因為如果不使用，在場景中的那些拐角處就會產生太多的信息點。這與Irradiance Cache的行為很相似。

For this reason, using the Irradiance Point Cloud as a secondary GI engine can sometimes create splotchy artifacts near corners or cause light leaks. The 「Retrace Threshold」 parameter prevents Brute-Force or Irradiance Cache from using points in these places. The larger the 「Retrace Threshold」 is, the more these points will not be used around corners and creases.

由於這個原因，用Irradiance Point Cloud為作Secondary GI引擎，有時會在拐角處出現斑塊或者發生漏光。Retrace Threshold參數會在這些區域抑制Brute Force或者 Irradiance Cache使用點信息計算。值越大意味著拐角和褶皺處有更多信息點被取消掉。

When using Irradiance Cache as the primary GI engine, values such as 1 or 2 as usually sufficient.

當使用Irradiance Cache作為Primary GI引擎時，用1或者2足以。

When using Brute-Force as the primary GI engine, values such as 2 or 3 are usually sufficient. Brute-Force is a more accurate technique than Irradiance Cache so any artifacts would be more visible. This is why this value has to be higher for Brute-Force than the Irradiance Cache.

當Brute Force作為Primary GI引擎時，可以用2或者3。Brute Force比Irradiance Cache更精確，因而更容易產生明顯的噪點。這就是Brute Force 比Irradiance Cache 需要更大的Retrace Threshold的原因。

How To Use如何使用

Using the Irradiance Point Cloud is very easy. All you have to do is select it as a secondary GI engine and (typically) only tweak 「Screen Radius」 and 「Samples Per Pixel」.

使用Irradiance Point Cloud很容易。只需要將它用於Secondary GI引擎，然後只需要調節Screen Radius和Sample Per Pixel。

First, we demonstrate the benefits of the Irradiance Point Cloud.

首先，我們來看使用Irradiance Point Cloud的優勢。

Both of the scenes shown below were rendered with the primary GI engine set to Brute-Force. 「Num Rays」 was set to a high number: 4000. There is 1 GI bounce in these scenes.

下面的兩個場景我們設置Primary GI 為Brute Force。Num Ray=4000。一次GI反彈。

The first image used Brute-Force for the secondary GI engine while the second image used Irradiance Point Cloud for the secondary GI engine. The second image was rendered approximately twice as fast and is cleaner, too!

Irradiance Point Cloud作為Secondary GI引擎，第二張圖渲染時間是第一張圖的一半，但和第一張圖一樣乾淨。

Using Brute-Force as the secondary GI engine. Even with 4000 rays, there is noise everywhere.

使用Brute-Force作為Secondary GI引擎。4000採樣射線，仍然到處是噪點。

Using the Irradiance Point Cloud as the secondary GI engine. The results are much cleaner and the frame was completed in nearly half the time.

使用Irradiance Point Cloud作為Secondary GI引擎。這個結果更乾淨，渲染節省一半的時間。

We will now demonstrate the effect of the Irradiance Point Cloud parameters.

然後再看看Irradiance Point Cloud參數作用。

The image below is using 「Screen radius」 of 4, 「Samples per pixel」 8, 「Filter Size」 3 and 「Retrace Threshold 0」. We intentionally made the retrace threshold 0 to demonstrate the splotchy effects near corners. These artifacts exist because the Irradiance Point Cloud was created with a fairly low number of samples per pixel (8), so the points are noisy. The recommended way to fix this issue is to use a larger retrace threshold. For Brute-Force values such as 3 or 4 work fine. For Irradiance Caching, you can use values like 1 or 2. Of course, there might be scenes that might not exhibit such issues – for these scenes you can lower the retrace threshold.

下圖Screen Radius=4，Samples Per Pixel=8，Filter Size=3，而Retrace Threshold=0。當我們設置Retrace Threshold=0時，會看到角落中有很多斑點污跡。這種污跡的存在是因為點雲初始Samples Per Pixel很低(8)，以至於信息點是充滿噪點的。我們意見解決方式是增加Retrace Threshold。如果使用Brute-Force作為Primary GI引擎的話，Retrace Threshold=3或者4。如果使用Irradiance Cache作為Primary GI引擎的話，Retrace Threshold=1或者2。當然，有些場景根本沒有噪點問題。那麼可以再降低retrace threshold。

Increasing 「Retrace Threshold」 means that the primary GI engine will not use the points near corners so, instead, it will have to shoot rays. Shooting rays is slower than simply using points, so increasing 「Retrace Threshold」 can make the rendering a bit slower during the Irradiance Cache computation stage (if Irradiance Cache is selected as the primary GI engine) or during final rendering (if Brute-Force is selected as the primary GI engine).

增加Retrace Threshold意味著Primary GI引擎在拐角處將不使用信息點，而使用更多的射線採樣。射線採樣花費的時間要比簡單的使用信息點要長，因此，增加Retrace Threshold會導致Irradiance Cache計算過程時間加長（如果Primary GI用是的Irradiance Cache）或者導致最終渲染時間變長（如果Primary GI引擎是Brute－Force）

Retrace Threshold set to 0. With 8 samples per pixel, the points are noisy so artifacts appear near corners

Retrace Threshold=0 Samples Per Pixel=8，信息點充滿噪點，因此在角落附近出現噪點。　

Now the samples per pixel was raised to 64 which make the Irradiance Point Cloud computation stage longer, but the corner artifacts were improved. There are still some, though.

現在Samples per Pixel=64，Irradiance Point Cloud時間更長，角落附近的噪點有改善，但斑點還是存在。

Using 8 samples per pixel but a retrace threshold of 3. The Irradiance Point Cloud computation was fast (because of the low 「Samples per pixel」) and doesn』t have issues. The final rendering was a bit slower, though.

Samples Per Pixel=8，但Retrace Threshold=3。Irradiance Point Cloud非常快（由於Samples Per Pixel很低）最終渲染速度儘管慢一點，但噪點沒有了。

The corner artifacts will typically be as large as 「Screen Radius」. This means that reducing 「Screen Radius」 will shrink the artifacts. Smaller artifacts also mean faster rendering times because 「Retrace Threshold」 will not have to work as hard.

拐角處的色斑通常與Screen Radius設定一樣大。也就是Screen Radius會縮小色斑。色斑小也意味著渲染更快。因為Retrace Threshold參數應該相應放鬆一些。

Because the Irradiance Cache can also generate corner artifacts (if its 「Num Rays」 is low or 「Adaptive Error Threshold」 is too high) it can sometimes be a bit confusing understanding which GI engine is responsible for these artifacts. There is a fairly simple rule of thumb: if you set your 「Retrace Threshold」 properly (i.e. 1 or 2 for the Irradiance Cache) and you are seeing corner artifacts then it』s most likely that it』s the Irradiance Cache itself that is responsible – and not the Irradiance Point Cloud.

由於Irradiance Cache也會在拐角產生色斑（如果Num Rays數值很小或者Adaptive Error Threshold設置很大）。這一點可能有點難以理解。有一些很簡單的規則經驗：如果正確設置了Retrace Threshold(比如1或者2，用於Irradiance Cache)，假如在拐角處有色斑，那麼大多情況是因為Irradiance Cache本身的設置造成的，這些噪點與Irradiance Point Cloud設置無關。

The pictures below use the Irradiance Cache as the primary GI engine. 「Retrace Threshold」 was set to 1.

下兩張圖Primary GI引擎是Irradiance Cache，Retrace Threshold設置為1。

Using Irradiance Cache as the primary GI engine. 「Num Rays」 set to 1000 and 「Adaptive Threshold」 set to 0.001. The corners exhibit artifacts because of the low 「Num Rays」

使用Irradiance Cache作為 Primary GI引擎。Num Rays設置為1000，Adaptive Threshold設置為0.001。拐角處出現了斑塊。這是因為Num Rays數太低造成的。

The Irradiance Cache 「Num Rays」 was raised to 4000 and the artifacts are now gone.

將Num Rays提高到4000斑塊消失了。

How to use 「Rebuild (prepass)」 and 「Load」 modes to improve/eliminate flickering artifacts

如何使用Rebuild （prepass）和Load模式減少斑塊污跡和人工效果

Note注意

Irradiance point cloud prepass/load modes are mostly useful when combining it with brute-force GI. If you are using the irradiance cache for your primary GI engine, then you should use the irradiance cache』s own prepass/load modes. While it would be possible to do multiple passes (create irradiance point cloud files with prepass, then set them to load/blend and then create the irradiance cache files, etc), this would be too elaborate and, in most cases, will provide minimal benefits.

在與Brute-Force GI引擎結合使用時，Irradiance Point Cloud的Prepass/Load模式非常有用。如果使用Irradiance Cache作為 Primary GI，則應該用Irradiance Cache自己的Prepass/Load模式。儘管可以將其細分為多個階段（首先用Prepass生成Irradiance Point Cloud信息文件，再將這些文件Load/blend，然後再生成Irradiance Cache文件等等），但這樣有些細化過度了。多數情況，這種細化並不能帶來多少真正的優化。

When combining the irradiance point cloud with brute-force GI, slight flickering artifacts might appear during animations. These artifacts are quite rare and mostly happen if the lighting conditions are very hard and not enough 「Samples per pixel」 have been used.

當使用Brute-Force GI與Irradiance Point Cloud配合的時候，動畫序列可能會有閃動。這種情況只有在燈光條件極為苛刻，且Sample Per Pixel設置不夠多的時候出現。

1、If you encounter any such artifacts, you can try the following procedure:如果你遇到這種情況，可以採取下方法：

First, select 「Rebuild (prepass)」 and select an appropriate filename – or use the default filename.

先將模式改為Rebuild（Prepass），並選取適當的文件名

2、Render your animation. During rendering, one irradiance point cloud file for each frame will be generated but the final rendering pass will be skipped.

渲染序列。此時每幀Irradiance Point Cloud文件會被計算生成，最終渲染序列不會產生。

3、Then, select the 「Load」 mode and adjust the 「number of frames to blend」 parameter. Render your animation. For each frame, Redshift will now load a number of 『neighboring frame』 irradiance point cloud files, blend them together and use the blended result to render the final frame. Because of this inter-frame blending, any temporal artifacts (flickering) will be reduced or even eliminated.

然後選擇Load模式，並調節Number Of Frames To blend參數，然後渲染序列。Redshift會在每一幀時讀取相領幀的Irradiance Point Cloud信息，並將它們混合在一起，用混合後的結果作為最終的渲染輸出。最終所有閃爍問題會被抑制或者消除。

The 「number of frames to blend」 parameter controls how many 『neighboring』 irradiance point cloud files will be loaded and blended together. For example, a setting of 2 means 「load the previous two and next two frames」. So, for this example, the algorithm will blend 4 neighboring frames plus the current frame, i.e. 5 frames together. A setting of 1 means 「load the previous and next frames」, so 3 frames will be blended together.

Number of frames to blend用於控制有多少相領的幀混合進來。2意味著之前2幀和之後的2幀都考慮進來。在這個例子中，相鄰的4幀和當前幀一共5幀被混合在一起。如果設為1，則表示前後兩幀加當前幀，共3幀混合。

Larger numbers of blended frames means less flickering. However, blending too many frames together can create a light 『ghosting』 or 『lagging』 effect in scenes with fast moving objects or lights. If your irradiance point cloud settings are properly adjusted, a setting between 2 and 4 should be sufficient to improve artifacts to the point of either being completely eliminated or barely visible.

數值越大，渲染結果閃爍缺少。混合太多幀的話會產生拖尾，只要設置Irradiance Point Cloud正確，2-4的值就能保證沒有閃爍問題。

Note注意：

Irradiance point cloud files can be large so be sure to select a folder/drive that has enough free space.

Irradiance Point Cloud 文件很大，需要確保指定位置有足夠的空間。

Memory Considerations內存管理

If you are rendering very high-resolution images and 「Screen Radius」 is low, you might get an error regarding the points not fitting in the allotted GPU memory space. The message will read like this:

如果渲染解析度很高Screen Radius又很小，可能會渲染出現錯誤，報告沒有足夠的GPU顯存空間。

Irradiance point cloud doesnt fit in VRAM. Frame aborted. Please either increase the Screen Radius parameter or the irradiance point cloud memory budget in the memory options

Irradiance Point Cloud無法載入顯存。忽略當前渲染。請增加Screen Radius參數或者在Memory Option中提高Irradiance Point Cloud顯存配額。

Like the message suggests, you have two options:遇到種情況，有兩個解決辦法：

1、Increase 「Screen Radius」. This should drastically reduce the memory requirements and, for high resolution images, will not affect image quality.

增大Screen Radius，這能極大程度節省顯存消耗。

2、Increase the Irradiance Point Cloud memory in the options. If your GPU has enough memory, you can try increasing the 64MB to something like 80MB or 120MB

增加Irradiance Point Cloud顯存設置。只要GPU有足夠的顯存可用，可以增加這個值到６４MB、80MB甚至120MB。

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