【W⁺】Line of Action 的觀念並沒有 2D 與 3D 的差別，是種視覺構圖的原則，能幫助表演的設計佈局（staging），包含 pose、動線、構圖等等。善用這些表演線條，能幫助故事的表達，也甚至能暗示即將開展的表演。Line of Action 是一種觀念，也是好用的工具。以下只做簡單的介紹，原文非常詳細，極推薦！
文章轉貼自 flooby nooby 部落格
Line of Action - Mickey's Christmas Carol
In animation, the term staging refers to the purpose of directing the audience's attention, and make it clear what is of greatest importance in a scene; what is happening, and what is about to happen. This can be done by various means, such as the placement of a character in the frame, the use of light and shadow, and the angle and position of the camera.
As shown in this post, the position and posture of the characters in the scene can greatly effect the staging and composition, in addition, it can help to place the characters within the situation, making them part of their environment and the story.
負空間（negative space） 與重疊（overlapping）：
The use of negative space and overlapping shapes for posing characters creates clear silhouettes, see the empty spaces between the arms and legs and major forms in these drawings
Another method is to create a strong line of action through your character. This helps your poses "read", it makes them clear and understandable and gives them a distinct non-ambiguous direction.
Here's some Preston Blair examples with Tom & Jerry:
如果你對傳統繪畫、攝影、漫畫、平面設計也有涉獵的話，你也會發現他們都運用相同的原則。甚至在大自然中，也能發現 lines of action 的定律。
If you study classical paintings, photography, comic books, and graphic design - you'll find that they all use this same principle. You need only to look at nature to find these lines of action:
試著假想這些 line of action 其實就是角色背後 ( 裡頭 ) 存在著的骨架，並揣想這些假想線將會如何支配或牽動你的角色，引領角色的表演。而這些線條也會是動畫師訂立 pose 的基本原則。
The one thing that will really bring your drawings to life is that 'line of action'. You can think of it as the back bone of a character or just as the imaginary line that dictates how the body will move. This line should always be used in setting up a pose.
當然，Lines of action 的原則不僅僅適用於角色，包括整體的 Layout 構圖，能幫助畫面創造出節奏、動線以及聚焦的效果。
Lines of action are not limited to characters alone, here's samples by Bill Peet on how invisible lines can be found in the overall layout of a well composed scene or illustration to create rhythm, flow, and a focal point within the shot:
許多 storyboard 藝術家和動畫師都會依據這個基本原則，來規劃表演的呈現。這些線條的設定不僅是視覺上的美感表現，也蘊藏了角色的情緒等等心理層面，最終轉化成具體而微的表情和肢體表演。
Most storyboard artists and animators follow this method as a basic principle for planning out the acting and motion of the animated characters - their attitude and behaviors become expressed through their physical body.