Computer Graphics Notes Part-I

   1. What is Computer Graphics?

●       Creation, Manipulation, and Storage of geometric objects (modeling) and their images (rendering)

●       Display those images on screens or hard copy devices

●       Image processing

●       Others: GUI, Haptics, Displays (VR)...

   2. What drives computer graphics?

●       Game Industry

–        The newest driving force in CG

●       Why?  Volume and Profit

●       This is why we have commodity GPUs

–        Focus on interactivity

–        Cost effective solutions

–        Avoiding computing and other tricks

–        Games drive the baseline

    3. The Advantages of Interactive Graphics

Today, high quality graphics displays of personal computer provide one of the most natural means of communicating with a computer

It provides tools for producing pictures not only of concrete, ‘real-world’ objects but also of abstract, synthetic objects, such as mathematical surfaces in 4D and of data that have no inherent geometry, such as survey results.
It has an ability to show moving pictures, and thus it is possible to produce animations with interactive graphics.

With interactive graphics use can also control the animation by adjusting the speed, the portion of the total scene in view, the geometric relationship of the objects in the scene to one another, the amount of detail shown and so on.

The interactive graphics provides tool called motion dynamics. With this tool user can move and tumble objects with respect to a stationary observer, or he can make objects stationary and the viewer moving around them. A typical example is walking thorough made by builder to show flat interior and building surroundings. In many case it is also possible to move both objects and view.

4. Applications of computer graphics.

n  Computer Aided Design (CAD)

n  Presentation Graphics

n  Computer Art

n  Entertainment (animation, games, …)

n  Education & Training

n  Visualization (scientific & business)

n  Image Processing

n  Graphical User Interfaces

     5. What is vector and raster graphics?

n  Raster Graphics

Raster images, also known as bitmap images are made up of pixels that are arranged in a grid. For instance, a desktop icon, like the one shown here, is a 32px by 32px image that is, it is made up of a table of pixels that has 32 rows and 32 columns. These tiny pixels have different color information and when combined, they form the image. Common raster or bitmap file formats are .bmp, .jpeg or .jpg, .gif, .png, .pict, .tiff, .pcx and .psd. You can edit a bitmap or raster image using Adobe Photoshop, Microsoft Paint, and The GIMP etc.

n  Vector graphics

Unlike raster images, vector images are made up mathematically defined geometric shapes like lines, shapes and curves, with additional attributes like color and fill. A vector image file basically contains information on these shapes such as where they start, what are their paths, the curve of the paths etc. Software draws the vector image by reading this data.

Common vector image formats are .ai, .cdr, .cmx, .dxf, .wmf. Most popular vector graphics editing programs are Adobe Illustrator and CorelDRAW.

6.Difference between Raster and Vector Graphics

1.     Raster or Bitmap images are resolution dependent. Because of this it’s not possible to increase or decrease their size without sacrificing on image quality.

When the size of a bitmap or raster image is reduced, some pixels must be thrown away. Thus losing some of the image’s data. When you increase its size, some new pixels must be created based on the color values of the surrounding pixels, which is not accurate thus affecting the quality of image.
Vector based images are not dependent on resolution. The size of vector image can be increased or decreased to any proportion without affecting the image’s quality. Fonts are a type of vector objects.

2.     Raster or bitmap images are always rectangular in shape. If you see a bitmap image with any other shape then it just means that the rest of the pixels have same color as the image’s background color. Vector images, however, can have any shape. For example, see the image here. The vector bitmap and the vector circle seem to be the same on a white background. However, on any other color, the difference is obvious as the bitmap circle’s white pixels are visible, thus proving its rectangular shape.

3.     Unlike bitmap/raster image, Vector images can’t be used for realistic images. This is because vector images are made up of solid color areas and mathematical gradients, so they can’t be used to show continuous tones of colors in a natural photograph.

You must have noticed that most of the vector images have a cartoon like appearance. The reason behind it is the same; vector graphics can’t display continuous variation in color. 

However, the vector graphics technology is advancing pretty fast, and in near future we may be able to get a bitmap like appearance in vector graphic.

All scanned images and images taken from digital cameras are raster or bitmap images. Vector images are basically created using software like Adobe Illustrator. It’s impossible to capture/scan an image and convert it into a vector format without using specialized conversion software. However, it’s very easy to convert a vector image to a raster image. This process is called rasterizing.

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Array in Vb.net

Array:-

An array stores a fixed-size sequential collection of elements of the same type. An array is used to store a collection of data, but it is often more useful to think of an array as a collection of variables of the same type.

All arrays consist of contiguous memory locations. The lowest address corresponds to the first element and the highest address to the last element.

Creating Arrays in VB.Net

To declare an array in VB.Net, you use the Dim statement. For example,

Dim intData(30)   ' an array of 31 elements

Dim strData(20) As String      ' an array of 21 strings

Dim twoDarray(10, 20) As Integer      'a two dimensional array of integers

Dim ranges(10, 100)    'a two dimensional array

You can also initialize the array elements while declaring the array. For example,

Dim intData() As Integer = {12, 16, 20, 24, 28, 32}

Dim names() As String = {"Karthik", "Sandhya", _

"Shivangi", "Ashwitha", "Somnath"}

Dim miscData() As Object = {"Hello World", 12d, 16ui, "A"c}

The elements in an array can be stored and accessed by using the index of the array. The following program demonstrates this:

Module arrayApl

   Sub Main()

      Dim n(10) As Integer  ' n is an array of 11 integers '

      Dim i, j As Integer

      ' initialize elements of array n '        

      For i = 0 To 10

          n(i) = i + 100 ' set element at location i to i + 100

      Next i

      ' output each array element's value '

      For j = 0 To 10

          Console.WriteLine("Element({0}) = {1}", j, n(j))

      Next j

      Console.ReadKey()

   End Sub

End Module

When the above code is compiled and executed, it produces the following result:

Element(0) = 100

Element(1) = 101

Element(2) = 102

Element(3) = 103

Element(4) = 104

Element(5) = 105

Element(6) = 106

Element(7) = 107

Element(8) = 108

Element(9) = 109

Element(10) = 110

Dynamic Arrays

Dynamic arrays are arrays that can be dimensioned and re-dimensioned as par the need of the program. You can declare a dynamic array using the ReDim statement.

Syntax for ReDim statement:

ReDim [Preserve] arrayname(subscripts)

Where,

• The Preserve keyword helps to preserve the data in an existing array, when you resize it.
• arrayname is the name of the array to re-dimension.
• subscripts specifies the new dimension.

Module arrayApl

   Sub Main()

      Dim marks() As Integer

      ReDim marks(2)

      marks(0) = 85

      marks(1) = 75

      marks(2) = 90

      ReDim Preserve marks(10)

      marks(3) = 80

      marks(4) = 76

      marks(5) = 92

      marks(6) = 99

      marks(7) = 79

      marks(8) = 75

      For i = 0 To 10

          Console.WriteLine(i & vbTab & marks(i))

      Next i

      Console.ReadKey()

   End Sub

End Module

When the above code is compiled and executed, it produces the following result:

0       85

1       75

2       90

3       80

4       76

5       92

6       99

7       79

8       75

9       0

10      0

Multi-Dimensional Arrays

VB.Net allows multidimensional arrays. Multidimensional arrays are also called rectangular arrays.

You can declare a 2-dimensional array of strings as:

Dim twoDStringArray(10, 20) As String

or, a 3-dimensional array of Integer variables:

Dim threeDIntArray(10, 10, 10) As Integer

The following program demonstrates creating and using a 2-dimensional array:

Module arrayApl

   Sub Main()

      ' an array with 5 rows and 2 columns

      Dim a(,) As Integer = {{0, 0}, {1, 2}, {2, 4}, {3, 6}, {4, 8}}

      Dim i, j As Integer

      ' output each array element's value '

      For i = 0 To 4

          For j = 0 To 1

              Console.WriteLine("a[{0},{1}] = {2}", i, j, a(i, j))

          Next j

      Next i

      Console.ReadKey()

   End Sub

End Module

When the above code is compiled and executed, it produces the following result:

a[0,0]: 0

a[0,1]: 0

a[1,0]: 1

a[1,1]: 2

a[2,0]: 2

a[2,1]: 4

a[3,0]: 3

a[3,1]: 6

a[4,0]: 4

a[4,1]: 8

Jagged Array

A Jagged array is an array of arrays. The follwoing code shows declaring a jagged array named scores of Integers:

Dim scores As Integer()() = New Integer(5)(){}

The following example illustrates using a jagged array:

Module arrayApl

   Sub Main()

      'a jagged array of 5 array of integers

      Dim a As Integer()() = New Integer(4)() {}

      a(0) = New Integer() {0, 0}

      a(1) = New Integer() {1, 2}

      a(2) = New Integer() {2, 4}

      a(3) = New Integer() {3, 6}

      a(4) = New Integer() {4, 8}

      Dim i, j As Integer

      ' output each array element's value

      For i = 0 To 4

          For j = 0 To 1

              Console.WriteLine("a[{0},{1}] = {2}", i, j, a(i)(j))

          Next j

      Next i

      Console.ReadKey()

   End Sub

End Module

When the above code is compiled and executed, it produces the following result:

a[0][0]: 0

a[0][1]: 0

a[1][0]: 1

a[1][1]: 2

a[2][0]: 2

a[2][1]: 4

a[3][0]: 3

a[3][1]: 6

a[4][0]: 4

a[4][1]: 8

The Array Class

The Array class is the base class for all the arrays in VB.Net. It is defined in the System namespace. The Array class provides various properties and methods to work with arrays.

Properties of the Array Class

The following table provides some of the most commonly used properties of the Array class:

S.N	Property Name & Description
1	IsFixedSize Gets a value indicating whether the Array has a fixed size.
2	IsReadOnly Gets a value indicating whether the Array is read-only.
3	Length Gets a 32-bit integer that represents the total number of elements in all the dimensions of the Array.
4	LongLength Gets a 64-bit integer that represents the total number of elements in all the dimensions of the Array.
5	Rank Gets the rank (number of dimensions) of the Array.

Methods of the Array Class

The following table provides some of the most commonly used methods of the Array class:

S.N	Method Name & Description
1	Public Shared Sub Clear (array As Array, index As Integer, length As Integer) Sets a range of elements in the Array to zero, to false, or to null, depending on the element type.
2	Public Shared Sub Copy (sourceArray As Array, destinationArray As Array, length As Integer) Copies a range of elements from an Array starting at the first element and pastes them into another Array starting at the first element. The length is specified as a 32-bit integer.
3	Public Sub CopyTo (array As Array, index As Integer) Copies all the elements of the current one-dimensional Array to the specified one-dimensional Array starting at the specified destination Array index. The index is specified as a 32-bit integer.
4	Public Function GetLength (dimension As Integer) As Integer Gets a 32-bit integer that represents the number of elements in the specified dimension of the Array.
5	Public Function GetLongLength (dimension As Integer) As Long Gets a 64-bit integer that represents the number of elements in the specified dimension of the Array.
6	Public Function GetLowerBound (dimension As Integer) As Integer Gets the lower bound of the specified dimension in the Array.
7	Public Function GetType As Type Gets the Type of the current instance (Inherited from Object).
8	Public Function GetUpperBound (dimension As Integer) As Integer Gets the upper bound of the specified dimension in the Array.
9	Public Function GetValue (index As Integer) As Object Gets the value at the specified position in the one-dimensional Array. The index is specified as a 32-bit integer.
10	Public Shared Function IndexOf (array As Array,value As Object) As Integer Searches for the specified object and returns the index of the first occurrence within the entire one-dimensional Array.
11	Public Shared Sub Reverse (array As Array) Reverses the sequence of the elements in the entire one-dimensional Array.
12	Public Sub SetValue (value As Object, index As Integer) Sets a value to the element at the specified position in the one-dimensional Array. The index is specified as a 32-bit integer.
13	Public Shared Sub Sort (array As Array) Sorts the elements in an entire one-dimensional Array using the IComparable implementation of each element of the Array.
14	Public Overridable Function ToString As String Returns a string that represents the current object (Inherited from Object).

For complete list of Array class properties and methods, please consult Microsoft documentation.

Example

The following program demonstrates use of some of the methods of the Array class:

Module arrayApl

   Sub Main()

      Dim list As Integer() = {34, 72, 13, 44, 25, 30, 10}

      Dim temp As Integer() = list

      Dim i As Integer

      Console.Write("Original Array: ")

      For Each i In list

          Console.Write("{0} ", i)

      Next i

      Console.WriteLine()

      ' reverse the array

      Array.Reverse(temp)

      Console.Write("Reversed Array: ")

      For Each i In temp

          Console.Write("{0} ", i)

      Next i

      Console.WriteLine()

      'sort the array

      Array.Sort(list)

      Console.Write("Sorted Array: ")

      For Each i In list

          Console.Write("{0} ", i)

      Next i

      Console.WriteLine()

      Console.ReadKey()

   End Sub

End Module

When the above code is compiled and executed, it produces the following result:

Original Array: 34 72 13 44 25 30 10

Reversed Array: 10 30 25 44 13 72 34

Sorted Array: 10 13 25 30 34 44 72

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