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The C# column
Transformation in GDI+ - II
 In
the last article we discussed various forms of transformations. We will now
see how to perform these transformations programmatically.
Look at the following Paint event handler.
private void Form1_Paint ( object sender,
PaintEventArgs e )
{
Graphics g = e.Graphics ;
Image myimg = Image.FromFile (
“C:\\palace.jpg” ) ;
Matrix mymat = new Matrix( ) ;
mymat.Scale ( -1, 1 ) ;
mymat.Translate ( -350, 0 ) ;
g.Transform = mymat ;
g.DrawImage ( myimg, 50, 50 ) ;
g.ResetTransform( ) ;
}
This code creates a mirror image. Here we have used a Static method FromFile(
) of the Image class, which returns a reference to the image, which we have
collected in myimg. Next, in order to create a transformation matrix we have
first created an object of the Matrix class. Since the Matrix class is declared
in the System.Drawing.Drawing2D namespace, we must declare this namespace in
our program.
We have scaled the matrix by passing –1 as the first parameter to the
Scale( ) method. Due to this all the x coordinates would be multiplied by –1.
After multiplying this matrix with the coordinates of the image the resultant
image would be the mirror image of the original. When we scale the coordinates
of an image by multiplying them with –1 the resulting coordinates become
negative. Hence they would not be visible as the top left corner of the form
is (0, 0). To bring the image back in the form we have to translate it by some
x and y values. Next we have assigned this resultant transformation matrix to
the Transform property of the Graphics object. There onwards everything that
gets drawn would be multiplied with the transformation matrix. For drawing the
image we have used the DrawImage( ) method.
Next, we will create an application that would display the
string “KICIT” and its shadow on a WinForm. In this program we shall
draw the shadow of the text before drawing the text, so that the text overlaps
the shadow making the shadow appear as if it is behind the text. We shall draw
the shadow using the same font as the original text and shall use gray colour
for it. The shadow size would then be required to keep half the size of the
original text and also to be sheared in the direction.
private void Form1_Paint ( object sender, PaintEventArgs e
)
{
Graphics g = e.Graphics ;
Matrix mymat = new Matrix( ) ;
mymat.Shear ( -1.4f, 0f ) ;
mymat.Scale ( 1, 0.5f ) ;
mymat.Translate ( 236, 170 ) ;
g.Transform = mymat ;
Font myfont = new Font ( “Times
New Roman”, 100 ) ;
SolidBrush mybrush = new SolidBrush ( Colour.Gray )
;
g.DrawString ( “K”, myfont, mybrush, 50,
50 ) ;
g.DrawString ( “I”, myfont, mybrush, 150,
50 ) ;
g.DrawString ( “C”, myfont, mybrush, 200,
50 ) ;
g.DrawString ( “I”, myfont, mybrush, 300,
50 ) ;
g.DrawString ( “T”, myfont, mybrush, 350,
50 ) ;
g.ResetTransform( ) ;
mybrush.Colour = Colour.DarkMagenta ;
g.DrawString ( “K”, myfont, mybrush, 50,
50 ) ;
mybrush.Colour = Colour.FromArgb ( 150, 0, 255, 255
) ;
g.DrawString ( “I”, myfont, mybrush, 150,
50 ) ;
LinearGradientBrush lgb = new
LinearGradientBrush ( new Point ( 200, 50 ),
new Point ( 350, 200 ),Colour.Brown, Colour.Yellow )
;
g.DrawString ( “C”, myfont, lgb, 200, 50
) ;
HatchBrush hb = new HatchBrush ( HatchStyle.DiagonalCross,
Colour.Blue, Colour.Red ) ;
g.DrawString ( “I”, myfont, hb, 300, 50
) ;
Image myimg = Image.FromFile ( @”C:\test.bmp”
) ;
TextureBrush tb = new TextureBrush ( myimg ) ;
g.DrawString ( “T”, myfont, tb, 350, 50
) ;
}
To create a transformation matrix we have firstly created an object of the
Matrix class. This object represents an identity matrix of size 3 x 3. We intend
to perform shearing, scaling and translation transformations. For this we have
called the methods Shear( ), Scale( ) and Translate( ) using the mymat object.
These methods manipulate the object by performing matrix multiplications as
discussed earlier. At the end of these calls, mymat object represents the transformation
matrix.
Next, we have set the Transform property of the Graphics class object g to mymat
object. Now whenever a shape is be drawn, the corresponding shape’s coordinate
matrix gets multiplied with the transformation matrix stored in mymat. Next
we have selected a SolidBrush of gray colour and used the DrawString( ) method
of the Graphics class to display the string. We have called ResetTransfrom(
) method that resets the world transformation matrix of this Graphics object
to the identity matrix. The identity matrix represents a transformation with
no scaling, rotation, or translation.
To display “K” we have used a solid brush of dark magenta colour.
To display “I” we have used a transparent brush. A brush can be
made transparent by using the FromArgb( ) method and passing an alpha component
as its first parameter. The alpha component specifies how opaque or transparent
a colour should be. The alpha value ranges from 0 (fully transparent) to 255
(fully opaque). The default value is 255 and hence if we do not pass any value
the colour created is always opaque.
In our program we have passed 150 as the first parameter to the FromArgb( )
method. This results in a semi-transparent colour. The string “I”
gets drawn with semi-transparent blue colour.
Next we have displayed “C” using a linear gradient brush. Here the
y coordinate of the second point passed to the constructor of the LinearGradientBrush
class does not match with the y coordinate of the first point and hence the
gradient fill is not horizontal.
The “I” is displayed using a hatch brush and lastly to display “T”,
we have used a texture brush. To the constructor of the TextureBrush class a
reference to an image, which is to be filled, is passed. We have used the Static
method FromFile( ) of the Image class to load the image. If you run the program,
you will see the string “KICIT” written as shown below.
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Yashavant Kanetkar, one of the first
Express Computer columnists, is an established software expert, speaker
and author with several best-sellers to his credit, including titles like
“Let Us C” and the “Fundas” series. Contact him at kanetkar@dcubesoft.com |
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