Clipping in the context of computer graphics is a method to selectively enable or disable rendering operations within a defined range of interest. Mathematically, clipping can be described with the terminology of constructive geometry. A rendering algorithm draws only pixels at the intersection between the clip area and the scene model (for example 3D configurator). Lines and areas outside the visible volume (frustum) are removed.
Clip areas are often specified to improve rendering performance. A well selected clip allows the renderer to save time and energy by skipping calculations to pixels that the user cannot see. The pixels to draw are inside the clipart. Pixels that are not drawn are outside the Clip Area. More informally, pixels that are not to be drawn are called clipped.
Clipping to 2D graphics.
In two-dimensional graphics, a clipart area can be defined so that pixels are only drawn within the boundaries of a window or frame. Clip areas can also be used to selectively control pixel rendering for aesthetic or artistic purposes. In many implementations, the final clip area is the composite (or intersection) of one or more application-defined shapes and any hardware limitations of the system.
In a sample application, an image editing program is recommended. A user application can render the image into a viewport. As the user zooms and scrolls to see a smaller portion of the image, the application can set a clip boundary so that pixels outside the viewport are not rendered. In addition, GUI widgets, overlays, and other windows or frames can hide some pixels from the original image. In this sense, the Clip Area is the interaction of the application-defined “User Clip” and the “Device Clip”, which is forced by the software and hardware implementation of the system. The application software can use this clip information to save computing time, energy and storage space and avoid working with pixels that are not visible.
Clipping to 3D graphics.
In three-dimensional graphics, the terminology of clipping can be used to describe many related features. Typically, “clipping” refers to operations in the plane that work with rectangular shapes, and “culling” to more general methods of selectively processing scene model elements. This terminology is not rigid, and the exact use varies from source to source.
Scene model elements include geometric primitives: points or nodes, line segments or edges, polygons or faces, and more powerful model objects such as curves, splines, faces, and even text. In complicated scene models, individual elements can be selectively deactivated (truncated), e.g. for reasons of visibility within the viewport (backface culling), orientation (backside alveation), darkening by other scenes or model elements (occlusion culling, depth or z clipping). There are sophisticated algorithms to efficiently detect and perform such clipping. Many optimized clipping methods are based on a specific hardware acceleration logic provided by a GPU.
The concept of clipping can be extended to a higher dimensionality using methods of abstract algebraic geometry.
In addition to corner point projection and 2D clipping, near clipping is required to correctly rasterize 3D primitives. This is because corner points may have been projected behind the eye. Near clipping ensures that all nodes used have valid 2D coordinates. Along with far clipping, it also helps prevent the depth buffer values from overflowing. Some early texture mapping devices (with forward texture mapping) in video games suffered from complications related to near clipping and UV coordinates.
Occlusion clipping (Z or Depth clipping).
In Depth clipping, “Z” often refers to the depth axis in the coordinate system, which is centered on the viewport origin: “Z” is used interchangeably with “Depth” and conceptually corresponds to the distance “into the virtual screen”. In this coordinate system, “X” and “Y” therefore refer to a conventional Cartesian coordinate system located on the user’s screen or viewport. This viewport is defined by the geometry of the field of view and parameterizes the field of view.
Z clipping or depth clipping refers to techniques that selectively render certain scene objects based on their depth relative to the screen. Most graphics toolkits allow the programmer to specify a “near” and “far” clip depth, and only parts of objects between these two layers are displayed. A creative application programmer can use this method to visualize the interior of a 3D object in the scene. For example, a medical imaging application could use this technique to visualize the organs in a human body. For example, a medical imaging application could use this technique to display the organs in a human body. A video game programmer can use clipping information to speed up game logic. For example, a high wall or building that closes other game units can save GPU time that would otherwise be spent transforming and texturing elements in the back of the scene, and a tightly integrated software program can use this information to save CPU time by optimizing game logic for objects not seen by the player.
The importance of clipping in video games.
A good clipping strategy is important when developing video games to maximize the frame rate and quality of the game. Despite GPU chips being faster every year, it is still computationally intensive to transform, texture and shade polygons, especially with today’s multiple textures and shadings. Therefore, game developers must live within a certain budget of polygons that can be drawn for any video game.
In order to maximize the visual quality of the game, developers prefer to make aesthetic choices rather than limit the hardware to the polygon budget. Optimizations that improve performance or take advantage of the acceleration of the graphics pipeline improve the gaming experience.
Clipping optimization can accelerate the rendering of the current scene and save render time and disk space within the hardware’s capabilities. Programmers often develop clever heuristics to speed up the clipper, as it is sometimes computationally unreasonable to use line casting or raytracing to determine which polygons are not in the camera’s field of view. Spatially conscious data structures such as octrees, R* trees, and bounding volume hierarchies can be used to divide scenes into rendered and unrendered areas (so the renderer can reject or accept entire tree nodes if necessary).
Occlusion optimizations based on the geometry of the angle of view can cause artifacts if the scene contains reflective surfaces. A common technique, reflection mapping, can use optional existing occlusion estimates from the Main Frustum View point of view or, if performance permits, calculate a new occlusion map from a separate camera position.
For historical reasons, some video games used Collision Detection optimizations with identical logic and hardware acceleration as the occlusion test. As a result, non-specialists have mistakenly used the term “clip” (and its anonym “no clipping”) to refer to collision detection.
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