BT9301, Computer Graphics

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Assignment

DRIVE	FALL 2014
PROGRAM	BSc IT
SEMESTER	SIXTH
SEMESTER CODE & NAME	BT9301, Computer Graphics
BK ID	B0810
CREDIT	4
MARKS	60

Note: Answer all questions. Kindly note that answers for 10 marks questions should be approximately of 400 words. Each question is followed by evaluation scheme.

1 Describe the architecture of vector display with diagram.

Answer: A vector monitor or vector display is a display device used for computer graphics up through the 1970s. It is a type of CRT, similar to the oscilloscope. In a vector display, the image is composed of drawn lines rather than a grid of glowing pixels as in raster graphics.

A vector signal analyzer is an instrument that measures the magnitude and phase of the input signal at a single frequency within the IF bandwidth of the instrument. The primary use is to make in-channel measurements, such as error vector magnitude, code domain power, and spectral flatness, on known signals.

2 Write and explain midpoint circle drawing algorithm.

Answer:  Algorithm: The objective of the algorithm is to find a path through the pixel grid using pixels which are as close as possible to solutions of x² + y² = r². At each step, the path is extended by choosing the adjacent pixel which satisfies x² + y² <= r² but maximizes x² + y² . Since the candidate pixels are adjacent, the arithmetic to calculate the latter expression is simplified, requiring only bit shifts and additions.

This algorithm starts with the circle equation. For simplicity, assume the center of the circle is at (0,0). We consider first only the first octant and draw a curve which starts at point (r,0) and proceeds counterclockwise, reaching the angle of 45.

3 What do you mean by polygon filling? Explain flood fill algorithm for polygon filling.

Answer: Algorithm that determines the area connected to a given node in a multi-dimensional array. It is used in the "bucket" fill tool of paint programs to determine which parts of a bitmap to fill with color, and in puzzle games such as Minesweeper, Puyo Puyo, Lumines, Samegame and Magical Drop for determining which pieces are cleared. When applied on an image to fill a particular bounded area with color, it is also known as boundary fill.

Alternative Improved Algorithm

v  Fill in row with START pixel

4 Write Liang Barkey’s line clipping algorithm. Write advantages of it.

Answer: Applet displays result of Liang-Barsky's Line Clipping Algorithm solution. There is initial line and clipping rectangle projected. The clipped part of initial line is highlighted by bolder and more contrast color. Interactivity affords to change parameters (positions of outer points and cornes) of initial line and clipping rectangle comfortably using mouse functionality:

v  Finding and marking closest flexible point

v  Drag & drop idea of relocation outer

5 What is shear? Explain X shear and Y shear.

Answer: Shear: Shearing in continuum mechanics refers to the occurrence of a shear strain, which is a deformation of a material substance in which parallel internal surfaces slide past one another. It is induced by a shear stress in the material. Shear strain is distinguished from volumetric strain, the change in a material's volume in response to stress.

Often, the verb shearing refers more

6 Briefly describe orthographic projection and oblique projection.

Answer: Orthographic projection: Orthographic projection (or orthogonal projection) is a means of representing a three-dimensional object in two dimensions. It is a form of parallel projection, where all the projection lines are orthogonal to the projection plane, resulting in every plane of the scene appearing in affine transformation on the viewing surface. It is further divided into multiview orthographic projections and axonometric projections. A lens providing an orthographic projection is known as an (object-space) telecentric lens.

The term orthographic is also sometimes reserved

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