Page 130 - DCAP504_Computer Graphics

Unit 8: 3-D in Computer Graphics

Clipping of a text can be categorized in the following ways:
1. Precise clipping
2. Clipping to a character
3. Clipping a text by words

Each text is seen as an inseparable object in the case of clipping. Every character consists of a rectangle
that is called as “rectangle envelope”. The center of the envelope is tested in the display box while
clipping two characters to each other.
8.3 3-D Viewing

The 3-D viewing process is much more complex than the 2-D viewing operations. Here projections are
implemented to convert 3-D objects into 2-D projection planes. Here, the view volume is specified in
the world coordinates using the modeling transformation. These transformations are next used in the
conversion process.
In 3-D viewing, a viewing volume specifies a viewing volume with a projection method in the world
coordinates, and a viewport on the display.
1. Viewing volume states what to appear
2. View port specifies where to display
For viewing an object, the camera and perspective projection is required. The camera properties are the
following:
1. Eye at a point in space
2. View volume whose apex is at the eye
3. Field of view θ
4. Near and far clipping images
5. View plane and its aspect ratio

8.3.1 The Viewing Pipeline
The 3-D viewing volume is processed for projection methods. Objects are clipped against the 3-D
viewing volume. The contents are then transformed into the viewport for display. The 3-D coordinates
are preserved for lighting and hidden-surface removal.
Graphic Pipeline in 3-D Viewing
In the case of 3-D viewing, a view volume is described in terms of world coordinates. The modeling
transformation is used for the same. The positions of world coordinates are transformed to viewing
coordinates with the implementation of viewing transformation. The description in viewing coordinates
is converted to 2-D projection coordinates using the projection transformation. In the final stage, the
projection coordinates are transformed into device coordinates through the workstation transformation.
The figure 8.11 depicts the pipeline.

Figure 8.11 : 3-D Viewing Pipeline

The stages in the graphic pipeline are responsible for information processing that are provided at initial
stages as just properties at the vertices or control points. They specify what has to be rendered. The

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