GAMBAS BOOK 3.19.1

The Gambas GUI toolkits QT and GTK implement gb.image.io, so it is not necessary to activate this component in the project properties if you want to create a GUI application. You only need to add gb.image.io if the application does not use a GUI toolkit, so that all properties and methods from gb.image.io methods are available to you.

This class is a new implementation of Image in gb.image. All image formats provided by the gdk-pixbuf library are supported (at least JPEG, PNG, BMP, GIF and XPM). The class can be created and works like a read and write array. The new implementation of Image in gb.image.io has been extended by 4 methods compared to Image (gb.image).

The Image class (gb.image.io) has these newly implemented methods:

Table 23.4.2.8.1 : Methods of the Image class

Notes:

The identifier for the function 'Stretch(…) is misleading. The function does not return a 'stretched version' of an image as a function value per se; only if a parameter - either Width or Height - is negative is the image proportion retained when the size is changed.

In this project, the two functions Load (Path As String) and Stretch (Width As Integer, Height As Integer) as well as the procedure Save (Path As String [ , Quality As Integer ]) are used.

You can use

• load an image (fractal.png) with a specified path,
• resize it within the specified limits for the image width and height and
• save the modified image (fractal.stretch.png) with the modified name.

This is the source code:

' Gambas class file
 
Public hImage As New Image
Public hImageMod As New Image
Public sPath As String
 
Public Sub Form_Open()
 
    FMain.Caption = "Image.Stretch"
 
End
 
Public Sub btnLoad_Click()
 
'-- Show the original image in PictureBox1
    hImage = Image.Load(Application.Path &/ "images/fractal.png")
 
'-- Show the original image in PictureBox1
    PictureBox1.Picture = hImage.Picture
 
'-- Stretch ( Width As Integer, Height As Integer )
    hImageMod = hImage.Stretch(spboxW.Value, spboxH.Value)
 
'-- Display the modified image in the PictureBox2
    PictureBox2.Picture = hImageMod.Picture
 
End
 
Public Sub spboxW_Change()
 
    PictureBox2.Picture = hImageMod.Stretch(spboxW.Value, spboxH.Value).Picture
 
End
 
Public Sub spboxH_Change()
 
  PictureBox2.Picture = hImageMod.Stretch(spboxW.Value, spboxH.Value).Picture
 
End
 
Public Sub btnSave_Click()
 
    If Not IsNull(hImageMod) Then hImageMod.Save(Application.Path &/ "images/fractal.stretch.png")
 
End

When the programme is started, the start parameters for the Stretch(…) function are set to W = 150 and H = 200:

Figure 23.4.2.8.1: Display after starting the programme

The parameters were then set to W = 120 and H = 370. The image proportion is not retained:

Figure 23.4.2.8.2: Display with changed parameters

However, if you set one of the two parameters - in this case the image width W - to (any) negative value and then change the image height H, the image is set to the selected image height and the image width is (automatically) changed so that the image proportion is retained:

Figure 23.4.2.8.3: Display with a negative parameter

The project is available in the download area as a project archive.