2006年出了兩篇關於SOFT SHADOW MAPS論文：
《Soft Shadow Maps： Efficient Sampling of Light Source Visibility》和
《Real-time soft shadow mapping by backprojection》
他們不同大學分別做出的類似技術。都是使用SHADOW MAPS處理和模糊陰影邊緣。軟陰影方面雖然SHADOW VOLUME走得更遠，但隨着梯形SHADOW MAPS，對數SHADOW MAPS等一些變形SHADOW MAPS成熟，硬件支持如果更加重視，也許未來陰影實用話方面SHADOW MAPS能夠超過VOLUME。畢竟VOLUME在模糊陰影邊緣方面有天生得弱勢。PRT或者其他的諧和函數方法模擬動態或靜態的低頻光源，或許是軟陰影的另一個方向。今後有時間把SHADOW一節展開來記錄一下。
先看看這兩篇相同時間相同內容的PAPER，它們是如何互相評價的.
from<Soft Shadow Maps:Effcient Sampling of Light Source Visibility>:
Guennebaud et al. [GBP06]（就是下一篇） also used the back projection
of each pixel in the shadow map to compute the soft shadow.
Their method was developed independently of ours, yet is
very similar. The main differences between the two methods
lie in the order of the computations: we compute the soft
shadow in shadow map space, while they compute the soft
shadow in screen space, requiring a search in the shadow
map.。。。言下之意，多一道手續，慢。。。
說到自己的缺陷：
Our algorithm also has some limitations when compared
to existing algorithms. First, our algorithm splits scene geometry
into occluders and receivers and self shadowing is
not accounted for. Also, since our algorithm uses shadow
maps to approximate occluder geometry, it inherits the well
known issues with aliasing from shadow map techniques.
For large area light sources, the soft shadows tend to blur
the artifacts but for smaller area light sources, such aliasing
is apparent.
這個方法沒有自陰影。。。遮擋物和接受物必須分開。受限很小的SHADOW MAP（應該指occluder map）。當面光源比較小後，走樣比較明顯。
看一下另一篇
from<Real-time soft shadow mapping by backprojection>:
In a very recent work [AHL*06], Atty et al. have
presented a soft shadow algorithm whith a percentage of
visibility computation based, as in our approach, on the back
projection of the shadow map samples. However, unlike
our algorithm, their method relies on a very restrictive
assumption: occluders and receivers are disjointed sets.
Moreover, they are limited to very small shadow map
resolution (they report 200×200 pixels) and because all
visibility computations are done in the discrete shadow map
space, shadows are more aliased. 真是直接。。。
