Computer Security

1. Functions of any five logical input devices and the associated examples for each type [15]
String
A string device is a logical device that provides ASCII strings to the user program. Usually, this
logical device is implemented by means of a physical keyboard. In this case, the terminology
is consistent with the terminology used in most window systems and OpenGL, which do not
distinguish between the logical string device and the keyboard.
Locator
A locator device provides a position in world coordinates to the user program. It is usually
implemented by means of a pointing device, such as a mouse or a trackball. In OpenGL, we
usually use the pointing device in this manner, although we have to do the conversion from
screen coordinates to world coordinates within our own programs. In other words, OpenGL
provides similar but conversion from screen coordinates to world coordinates must be made
by a user
Pick
A pick device returns the identifier of an object to the user program. It is usually
implemented with the same physical device as a locator, that is, a mouse or a trackball but
has a separate software interface to the user program. In OpenGL, we can use a process
called selection to accomplish picking.
Choice
Choice devices allow the user to select one of a discrete number of options. In OpenGL, we
can use various widgets provided by the window system. A widget is a graphical interactive
device, provided by either the window system or a toolkit. Typical widgets include menus,
scrollbars, and graphical buttons. Most widgets are implemented as special types of
windows. For example, a menu with n selections acts as choice device, allowing us to select
one of n alternatives.
Stroke
A stroke device returns an array of locations. Although we can think of a stroke as similar to
multiple uses of a locator, it is often implemented differently, such that an action, such as
pushing down a mouse button, starts the transfer of data into the specified array, and a
second action, such as releasing the button, ends this transfer
Dial
Dials (or valuators) provide analog input to the user program. Here again, widgets within
various toolkits usually provide this facility through graphical devices, such as slidebars.
2. (a) Definition of rendering [2]
Rendering is the process of converting your designed objects with texturing and
animation into an image or a series of images. Here various parameters are available like
resolution, colors, type of render etc.
Rendering is the process of generating an image from a 2D or 3D model (or models in
what collectively could be called a scene file), by means of computer programs

(b) Stages of graphics pipeline and the coordinate systems [8]

Graphics pipeline refers to the sequence of steps used to create a 2D raster
representation of a 3D scene.
3D geometric primitives
First, the scene is created out of geometric primitives. Traditionally this is done using
triangles, which are particularly well suited to this as they always exist on a single plane.
Modeling and transformation
Transform from the local coordinate system to the 3d world coordinate system. A model of a
teapot in abstract is placed in the coordinate system of the 3d world.
Camera transformation
Transform the 3d world coordinate system into the 3d camera coordinate system, with the
camera as the origin
Lighting
Illuminate according to lighting and reflectance. If the teapot is a brilliant white color, but in a
totally black room, then the camera sees it as black. In this step the effect of lighting and
reflections are calculated.
Projection transformation
Transform the 3D world coordinates into the 2d view of the camera, for instance the object
the camera is centered on would be in the center of the 2d view of the camera.
[3]
In the case
of a Perspective projection, objects which are distant from the camera are made smaller. This
is achieved by dividing the X and Y coordinates of each vertex of each primitive by its Z
coordinate (which represents its distance from the camera). In an orthographic projection,
objects retain their original size regardless of distance from the camera.
Clipping
Geometric primitives that now fall completely outside of the viewing frustum will not be
visible and are discarded at this stage.
Scan conversion or rasterization
Rasterization is the process by which the 2D image space representation of the scene is
converted into raster format and the correct resulting pixel values are determined. From now
on, operations will be carried out on each single pixel. This stage is rather complex, involving
multiple steps often referred as a group under the name of pixel pipeline.
Texturing, fragment shading
At this stage of the pipeline individual fragments (or pre-pixels) are assigned a color based on
values interpolated from the vertices during rasterization, from a texture in memory, or from
a shader program.
3. Fully explain with the aid of a diagram how an LCD monitor operates. [10]
LCD monitors are used more commonly today in laptops and other electronic devices that
require high resolution or run on a battery (an LCD monitor is more battery efficient and
mobile than a CRT monitor). LCD display works by either allowing daylight to be reflected
back out at the viewer or preventing it from doing so - in which case the viewer sees a black
area. The liquid crystal is the part of the system that either prevents light from passing
through it or not. In other words, An LCD monitor works by containing a liquid crystal, which
reacts to electrons, between two polarized glass plates.
The crystal is placed between two polarising filters that are at right angles to each other and
together block light. When there is no electric current applied to the crystal, it twists light by
90
o
, which allows the light to pass through the second polariser and be reflected back. But
when the voltage is applied, the crystal molecules align themselves, and light cannot pass
through the polariser: the segment turns black.
Rather than creating a certain type of color, the idea of an LCD monitor is to block out all
other colors, allowing only one wavelength to pass through the glass. This is interpreted by
our brains as color. The initial light comes from a backlight, which covers the entire section of
the screen. Electrical current moves through these little areas to modify which colors the
crystal blocks out. This gives a general outline shape, with color, to the images that the
computer wants to project. On top of the polarized glass plates is a series of transistors (this
layer of transistors is so thin that it seems to be translucent) which, when an electrical
current is passed through them, lights up these pixels, which adds definition to the entire
picture being projected. Below is a diagram displaying the inner workings of an LCD monitor