3D graphics eBook - Course Materials Repository
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3D graphics eBook - Course Materials Repository

3D graphics eBook - Course Materials Repository 3D graphics eBook - Course Materials Repository

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Voxel 247 General purpose voxel editors There are a few voxel editors available that are not tied to specific games or engines. They can be used as alternatives or complements to traditional 3D vector modeling. Extensions A generalization of a voxel is the doxel, or dynamic voxel. This is used in the case of a 4D dataset, for example, an image sequence that represents 3D space together with another dimension such as time. In this way, an image could contain 100×100×100×100 doxels, which could be seen as a series of 100 frames of a 100×100×100 volume image (the equivalent for a 3D image would be showing a 2D cross section of the image in each frame). Although storage and manipulation of such data requires large amounts of memory, it allows the representation and analysis of spacetime systems. References [1] Novelline, Robert. Squire's Fundamentals of Radiology. Harvard University Press. 5th edition. 1997. ISBN 0674833392. [2] "OUTCAST - Technology: Paradise" (http:/ / web. archive. org/ web/ 20100615185127/ http:/ / www. outcast-thegame. com/ tech/ paradise. htm). outcast-thegame.com. Archived from the original (http:/ / www. outcast-thegame. com/ tech/ paradise. htm) on 2010-06-15. . Retrieved 2009-12-20. [3] "VANGERS" (http:/ / www. kdlab. com/ vangers/ eng/ features. html). kdlab.com. . Retrieved 2009-12-20. [4] http:/ / voxelstein3d. sourceforge. net/ [5] Ars Technica. "We

Z-buffering 248 Z-buffering In computer graphics, z-buffering is the management of image depth coordinates in three-dimensional (3-D) graphics, usually done in hardware, sometimes in software. It is one solution to the visibility problem, which is the problem of deciding which elements of a rendered scene are visible, and which are hidden. The painter's algorithm is another common solution which, though less efficient, can also handle non-opaque scene elements. Z-buffering is also known as depth buffering. When an object is rendered by a 3D graphics card, the depth of a generated pixel (z coordinate) is stored in a buffer (the z-buffer or depth buffer). This buffer is usually arranged as a two-dimensional array (x-y) with one element for each screen pixel. If another object of the scene must be rendered in the same pixel, the graphics card compares the two depths and chooses the one closer to the observer. The chosen depth is then saved to the z-buffer, replacing the old one. In the end, the z-buffer will allow the graphics card to correctly Z-buffer data reproduce the usual depth perception: a close object hides a farther one. This is called z-culling. The granularity of a z-buffer has a great influence on the scene quality: a 16-bit z-buffer can result in artifacts (called "z-fighting") when two objects are very close to each other. A 24-bit or 32-bit z-buffer behaves much better, although the problem cannot be entirely eliminated without additional algorithms. An 8-bit z-buffer is almost never used since it has too little precision. Uses Z-buffer data in the area of video editing permits one to combine 2D video elements in 3D space, permitting virtual sets, "ghostly passing through wall" effects, and complex effects like mapping of video on surfaces. An application for Maya, called IPR, permits one to perform post-rendering texturing on objects, utilizing multiple buffers like z-buffers, alpha, object id, UV coordinates and any data deemed as useful to the post-production process, saving time otherwise wasted in re-rendering of the video. Z-buffer data obtained from rendering a surface from a light's POV permits the creation of shadows in a scanline renderer, by projecting the z-buffer data onto the ground and affected surfaces below the object. This is the same process used in non-raytracing modes by the free and open sourced 3D application Blender. Developments Even with small enough granularity, quality problems may arise when precision in the z-buffer's distance values is not spread evenly over distance. Nearer values are much more precise (and hence can display closer objects better) than values which are farther away. Generally, this is desirable, but sometimes it will cause artifacts to appear as objects become more distant. A variation on z-buffering which results in more evenly distributed precision is called w-buffering (see below). At the start of a new scene, the z-buffer must be cleared to a defined value, usually 1.0, because this value is the upper limit (on a scale of 0 to 1) of depth, meaning that no object is present at this point through the viewing frustum.

Voxel 247<br />

General purpose voxel editors<br />

There are a few voxel editors available that are not tied to specific games or engines. They can be used as<br />

alternatives or complements to traditional <strong>3D</strong> vector modeling.<br />

Extensions<br />

A generalization of a voxel is the doxel, or dynamic voxel. This is used in the case of a 4D dataset, for example, an<br />

image sequence that represents <strong>3D</strong> space together with another dimension such as time. In this way, an image could<br />

contain 100×100×100×100 doxels, which could be seen as a series of 100 frames of a 100×100×100 volume image<br />

(the equivalent for a <strong>3D</strong> image would be showing a 2D cross section of the image in each frame). Although storage<br />

and manipulation of such data requires large amounts of memory, it allows the representation and analysis of<br />

spacetime systems.<br />

References<br />

[1] Novelline, Robert. Squire's Fundamentals of Radiology. Harvard University Press. 5th edition. 1997. ISBN 0674833392.<br />

[2] "OUTCAST - Technology: Paradise" (http:/ / web. archive. org/ web/ 20100615185127/ http:/ / www. outcast-thegame. com/ tech/ paradise.<br />

htm). outcast-thegame.com. Archived from the original (http:/ / www. outcast-thegame. com/ tech/ paradise. htm) on 2010-06-15. . Retrieved<br />

2009-12-20.<br />

[3] "VANGERS" (http:/ / www. kdlab. com/ vangers/ eng/ features. html). kdlab.com. . Retrieved 2009-12-20.<br />

[4] http:/ / voxelstein3d. sourceforge. net/<br />

[5] Ars Technica. "We

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