AspJpeg.NET enables you to place images on top of each other via the method
JpegCanvas.DrawImage. The most basic overload of this method
expects three arguments: the X and Y offsets relative the upper-left corner of the background image,
and another instance of the JpegImage object representing the image to be drawn.
JpegManager objJpeg = new JpegManager();
JpegImage objBackground = objJpeg.OpenImage( strPath1 );
JpegImage objImage = objJpeg.OpenImage( strPath2 );
objBackground.Canvas.DrawImage( 10, 10, objImage );
The following code sample creates a "front page" for an online album
which contains the album title (aligned to the center) and up to 3 thumbnails
of the images read from a folder.
To create a blank image, the JpegManager.CreateImage method is used which accepts
the image dimensions and background color as arguments.
To align a text string to the right, the method JpegCanvas.GetTextExtent is used.
| C# |
|---|
<%@ Page Language="C#" debug="true" %>
<%@ Import Namespace="System.IO"%>
<%@ Import Namespace="Persits.Jpeg"%>
<html>
<head>
<title>AspJpeg.NET User Manual Chapter 6 - Picture-in-Picture</title>
<script runat="server" languge="C#">
void Page_Load( Object Source, EventArgs E)
{
// Source directory with images
string strPath = Server.MapPath("../images");
// Ablum title
string strTitle = "My Favorite Photographs";
// Create instance of JpegManager
JpegManager objJpeg = new JpegManager();
// Font path
string strFont = objJpeg.WindowsDirectory + @"\Fonts\arial.ttf";
// Create blank image for front page, white background
JpegImage objBkImage = objJpeg.CreateImage(380, 150, 0xFFFFFFFF);
// Draw 1-pixel blue frame
objBkImage.Canvas.Pen.Color = 0x000080;
objBkImage.Canvas.Pen.Width = 2;
objBkImage.Canvas.DrawRect(1, 1,
objBkImage.Width-2, objBkImage.Height-2);
// Draw album title
objBkImage.Canvas.Font.Size = 14;
int nTitleWidth = objBkImage.Canvas.GetTextExtent(strTitle, strFont);
objBkImage.Canvas.PrintText(strTitle,
(objBkImage.Width - nTitleWidth) / 2, 24, strFont);
// Enumerate images in the source directory
String[] files = Directory.GetFiles( strPath, "*.*");
int nCount = 0;
foreach (string strFile in files)
{
String strExt = Path.GetExtension(strFile).ToUpper();
if (strExt != ".JPG" && strExt != ".GIF" &&
strExt != ".TIF" && strExt != ".PNG")
continue;
// Draw this image on front page
JpegImage objImage = objJpeg.OpenImage(strFile);
// Resize to inscribe in 100x100 square
objImage.PreserveAspectRatio = true;
if(objImage.OriginalWidth>100 || objImage.OriginalHeight>100)
{
if (objImage.OriginalWidth > objImage.OriginalHeight)
{
objImage.Width = 100;
}
else
{
objImage.Height = 100;
}
}
int X = 20 + 120 * nCount;
int Y = 40;
// Center image inside frame vert or horiz as needed
objBkImage.Canvas.DrawImage(X + (100 - objImage.Width) / 2,
Y + (100 - objImage.Height) / 2, objImage);
// Draw frame for each thumbnail
objBkImage.Canvas.Pen.Width = 1;
objBkImage.Canvas.DrawRect(X - 1, Y - 1, 100, 100);
// Limit total images drawn to 3
nCount++;
if (nCount >= 3)
break;
}
string strFilename =
objBkImage.SaveUnique(Server.MapPath("frontpage.jpg"));
OutputImage.ImageUrl = strFilename;
}
</script>
</head>
<form runat="server">
<asp:image runat="server" id="OutputImage"/>
</form>
</html>
|
| VB.NET |
|---|
<%@ Page Language="vb" debug="true" %>
<%@ Import Namespace="System.IO"%>
<%@ Import Namespace="Persits.Jpeg"%>
<html>
<head>
<title>AspJpeg.NET User Manual Chapter 6 - Picture-in-Picture</title>
<script runat="server" languge="vb">
Sub Page_Load(Source As Object, E As EventArgs)
' Source directory with images
Dim strPath As String = Server.MapPath("../images")
' Ablum title
Dim strTitle As String = "My Favorite Photographs"
' Create instance of JpegManager
Dim objJpeg As JpegManager = New JpegManager()
' Font path
Dim strFont As String=objJpeg.WindowsDirectory+"\Fonts\arial.ttf"
' Create blank image for front page, white background
Dim objBkImage As JpegImage =
objJpeg.CreateImage(380, 150, &HFFFFFFF)
' Draw 1-pixel blue frame
objBkImage.Canvas.Pen.Color = &H80
objBkImage.Canvas.Pen.Width = 2
objBkImage.Canvas.DrawRect(1, 1,
objBkImage.Width - 2, objBkImage.Height - 2)
' Draw album title
objBkImage.Canvas.Font.Size = 14
Dim nTitleWidth As Integer =
objBkImage.Canvas.GetTextExtent(strTitle, strFont)
objBkImage.Canvas.PrintText(strTitle,
(objBkImage.Width - nTitleWidth) / 2, 24, strFont)
' Enumerate images in the source directory
Dim files() As String = Directory.GetFiles(strPath, "*.*")
Dim nCount As Integer = 0
For Each strFile As String In files
Dim strExt As String = Path.GetExtension(strFile).ToUpper()
If strExt <> ".JPG" And strExt <> ".GIF" And
strExt <> ".TIF" And strExt <> ".PNG" Then
Continue For
End If
' Draw this image on front page
Dim objImage As JpegImage = objJpeg.OpenImage(strFile)
' Resize to inscribe in 100x100 square
objImage.PreserveAspectRatio = True
If objImage.OriginalWidth>100 Or objImage.OriginalHeight>100 Then
If objImage.OriginalWidth > objImage.OriginalHeight Then
objImage.Width = 100
Else
objImage.Height = 100
End If
End If
Dim X As Integer = 20 + 120 * nCount
Dim Y As Integer = 40
' Center image inside frame vert Or horiz as needed
objBkImage.Canvas.DrawImage(X + (100 - objImage.Width) / 2,
Y + (100 - objImage.Height) / 2, objImage)
' Draw frame for each thumbnail
objBkImage.Canvas.Pen.Width = 1
objBkImage.Canvas.DrawRect(X - 1, Y - 1, 100, 100)
' Limit total images drawn to 3
nCount = nCount + 1
If nCount >= 3 Then Exit For
Next
Dim strFilename As String =
objBkImage.SaveUnique(Server.MapPath("frontpage.jpg"))
OutputImage.ImageUrl = strFilename
End Sub
</script>
</head>
<form runat="server">
<asp:image runat="server" id="OutputImage"/>
</form>
</html>
|
Click the links below to run this code sample:
http://localhost/aspjpeg.net/manual_06/06_frontpage.cs.aspx
http://localhost/aspjpeg.net/manual_06/06_frontpage.vb.aspx
6.4.1 Opacity & Transparency
The DrawImage method also provides three optional arguments to specify opacity and
transparency parameters.
When the basic overload of the DrawImage method described above is called, the image being drawn is fully opaque (non-transparent),
unless it has an alpha channel (discussed below).
To draw the image with an arbitrary degree of transparency, the overloaded version of DrawImage which expects a fourth argument of the type double
should be called.
This fourth argument controls the opacity of the image being drawn. It is a number between 0 and 1.
The value of 0 means the image is
to be displayed fully transparent (invisible), and 1
fully opaque.
The following code draws an image at 50% opacity:
objPhoto.Canvas.DrawImage( 50, 20, objLogo, 0.5 );
Certain pixels of an image can be made transparent when
this image is placed on top of another image. The color
of pixels to be made transparent is specified via yet another overload of the DrawImage method,
which takes a fourth argument of the type uint.
The following code makes all red pixels of an image transparent
when displayed on top of another image:
objPhoto.Canvas.DrawImage( 50, 20, objLogo, 0xFF0000 );
Since JPEG uses lossy compression, pixel colors often get slightly
distorted (although it may not be visible to the human eye).
For example, one or all color components of a pixel may change from 255 (FF)
to 254 during JPEG compression. To accommodate for this
distortion, there is yet another DrawImage overload that in addition to the transparency color, also takes
an allowable deviation from that color.
This number must be between 0 and 255 and affects all three color components
of a pixel. For example, the following code turns transparent all pixels
in the range 0x16D636 to 0x2AEA4A:
objPhoto.Canvas.DrawImage( 50, 20, objLogo, 0x20E040, 10 );
Finally, there is a DrawImage overload that takes all the arguments described above at once.
The following code makes all the red pixels with the deviation of 15 fully transparent,
plus applies a 30% opacity to all other pixels.
objPhoto.Canvas.DrawImage( 50, 20, objLogo, 0.3, 0xFF0000, 15 );
