Clipping path
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[edit] In 2D Graphics
In 2D computer graphics, a clipping path is a closed vector path, or shape, used to cut out an image in current image editing software. Anything inside the path will be included after the clipping path is applied; anything outside the path will be omitted from the output. Applying the clipping path results in a hard edge.
As an analogy, think of a cookie cutter. The shape of the cookie cutter describes the clipping path. The dough is analogous to the image the path is applied to. After the cutter is pressed in, everything outside of it is removed. The remaining image (or cookie in the analogy) has a clearly defined edge.
The inside of the path is defined by its direction. Reversing the direction of a path reverses what is considered inside or outside. An inclusive path is one where what is visually "inside" the path corresponds to what will be preserved; an exclusive path, of opposite direction, contains what is visually "outside" the path. By convention, a clockwise path that is non-self-intersecting is considered inclusive.
A compound path results from the combination of multiple paths (inclusive and exclusive) and the Boolean operations that ultimately determine what the combined path contains. For instance, an inclusive path which contains a smaller exclusive path results in a shape with a "hole" (defined by the exclusive path).
One common use of a clipping path is to cull objects that do not need to be rendered because they are outside the user's viewport or obscured by display elements (such as an HUD).
[edit] In 3D Graphics
Clipping planes are used in 3D computer graphics in order to prevent the renderer from calculating surfaces at an extreme distance from the viewer. The plane is perpendicular to the camera, a set distance away (the threshold), and occupies the entire viewport. Used in real-time rendering, clipping planes can help preserve processing for objects within clear sight.
The use of clipping planes can result in a detraction from the realism of a scene, as the viewer may notice that everything at the threshold is not rendered correctly or seems to (dis)appear spontaneously. The addition of fog—a variably transparent region of color or texture just before the clipping plane—can help soften the transition between what should be in plain sight and opaque, and what should be beyond notice and fully transparent, and therefore does not need to be rendered.
