Page 148 - DCAP504_Computer Graphics

Unit 9: Clipping I

9.5 Keywords

Device Co-ordinate: A device co-ordinate is a device-dependent co-ordinate system. The origin is at the
upper left corner, X increases to the left, Y increases down. As its units are pixels it is also known as
pixel co-ordinates.
GNOME: GNU Object Model Environment.
Viewport: It is a window manager window in computer graphics. It is basically a rectangular viewing
region.
Window Manager System: It controls the appearance of the windows within a windowing system in a
graphical user interface.
9.6 Self Assessment
1. State whether the following are true or false:
(a) When you input and transform the picture of the object in the window on the screen
viewport, the picture regions surrounding the window frame also disappears.
(b) In point clipping, the edges of the clip window can either be world-co-ordinate window
boundaries or viewport boundaries.

(c) If the line is either completely visible or completely invisible, then the line is clipping
candidate.
(d) The point whose region code is 0000 is inside the clipping window.
(e) In Midpoint Subdivision Algorithm, the subdividing process is repeated until you get the
completely visible or completely invisible line segment.

(f) The equation xwmin ≤ x0 + u ∆ x corresponds to the right hand clipping boundary.
2. Fill in the blanks:

(a) In computer graphics, the portion that is left outside the window frame is called as
…………………..
(b) The ………………….. reduces the calculations by linking the viewing and geometric
transformation matrices.

(c) The line clipping depends on the position of the endpoints with reference to the
…………………..
(d) A 4-bit binary code, called as ………………….., is assigned to each endpoint of the line.
(e) Cyrus and Beck developed a line-clipping algorithm which was based on …………………..
3. Select the suitable choice for every question:

(a) The picture regions against which the object is to clip is called as a ……………………….
(i) Clip window
(ii) World-co-ordinate
(iii) Clipping candidate
(iv) Clipped part

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