1.3 LINE DRAWING
• A wireframe object is simply rendered using the lines (straight, and curved) in a geometric model, then it is converted to screen coordinates using the Perspective Transformation.
• The process is as pictured below,
• If the geometric model is in some other form, such as CSG (Constructive Solids Geometry), it may have to be converted to lines before it may be used.
• Advantages,
- Very fast, allows real time manipulation
- Easy to see features normally hidden
- Supported by almost all computer technology
- This display method works with most displays
• Disadvantages,
- Drawings can become very crowded, very fast
- Hard to visualize solid properties
• Almost all computer graphics packages offer a wireframe display option.
1.3.1 Hidden Lines
• While the results seem similar, this method requires more sophisticated algorithms.
• Polygons must be used for surface representation.
• The diagram below shows the basic steps in the method of rendering
• Advantages,
- similar advantages of wireframe
- overcomes the drawing crowding
- can be simplified if polygons do not overlap
• Disadvantages,
- Consumes more computer time
- Does not support simple elemental geometric models
• Clipping algorithms may be difficult, and often use tricks like subdividing polygons into triangles. (There are only 5 cases to consider with overlapping triangles)
