GAMBAS BOOK 3.19.1

The project Bild-Lupe was created from the adapted source code by Fabien Bodard for his sample project MapView, which you can read about in connection with the component gb.map in → Chapter 24.8.0 'Component Map'. The source code for the project Bild-Lupe was optimised by Fabien Bodard during the testing phase.

Figure 23.3.5.4.1: Image magnifier as an impressive effect

In contrast to the MapView example project, the image magnifier is permanently switched on. The zoom can be continuously changed from value 1 (Image:Original=1) to value 3 using a slider. The most notable change compared to the MapView project is the use of a timer, with which the image is always redrawn in small time intervals.

Source code:

[1] ' Gambas class file
[2] 
[3] Private $sFile As String
[4] Private $hImage As Image
[5] Private $himgZoom As Image
[6] Private $iLensSize As Integer = 256
[7] Private $fZoom As Float = 2
[8] Private $bMouseDown As Boolean
[9] Private $MX As Integer
[10] Private $MY As Integer
[11] 
[12] ' Special technique to delay and cumulate drawing events
[13] ' In some case of too numerous call this allow to reduce it to one call by event loop
[14] ' The timer means that many - otherwise necessary - evaluations of the event loop are
[15] ' reduced to one call: $TimerDraw.Trigger()
[16] 
[17] Private $TimerDraw As Timer
[18] 
[19] Public Sub _new()
[20]   $TimerDraw = New Timer As "TimerDraw"
[21]   $TimerDraw.Delay = 5
[22] End 
[23] 
[24] Public Sub Form_Open()
[25]   FMain.H = 636
[26]   FMain.W = 806
[27]   FMain.Center
[28]   $sFile = "fractal.jpg"
[29]   Try $hImage = Image.Load($sFile)
[30]   If Error Then 
[31]      Message(Error.Text)
[32]      Return
[33]   Endif
[34]   Slider1.Value = 200
[35]   lblDisplayZoom.Text = ("Zoom-Factor = ") & Str(Slider1.Value / 100)
[36]   ScrollArea1.ResizeContents($hImage.Width, $hImage.Height)
[37]   $TimerDraw.Trigger ' Call refreshing
[38] End
[39] 
[40] Public Sub btnFileOpen_Click()  
[41]   Dialog.Path = User.Home
[42]   Dialog.Title = ("Select an image ...")
[43]   Dialog.Filter = (["*.png;*.jpg", ("Images")])
[44]   If Not Dialog.OpenFile() Then
[45]      $sFile = Dialog.Path
[46]      Try $hImage = Image.Load($sFile)
[47]      If Error Then 
[48]         Message(Error.Text)
[49]         Return
[50]      Endif
[51]      ScrollArea1.ResizeContents($hImage.Width, $hImage.Height)
[52]      $TimerDraw.Trigger
[53]   Endif  
[54] End
[55] 
[56] Public Sub ScrollArea1_Draw()
[57]   
[58]   If Not $hImage Then Return
[59]   
[60]   Paint.DrawImage($hImage, 0 - ScrollArea1.ScrollX, 0 - ScrollArea1.ScrollY, $hImage.Width, $hImage.Height)
[61]   If $bMouseDown Then
[62]      Paint.LineWidth = 2
[63]      Paint.Brush = Paint.Image($himgZoom, $mx - $iLensSize / 2, $my - $iLensSize / 2)   
[64]      Paint.Arc($MX, $MY, $iLensSize / 2)
[65]      Paint.Fill(True)    
[66]      Paint.Brush = Paint.Color(Color.Blue)
[67]      Paint.Stroke()    
[68]   Endif
[69]   
[70] End
[71] 
[72] Public Sub ScrollArea1_MouseDown()
[73]   ScrollArea1_MouseMove
[74] End
[75] 
[76] Public Sub ScrollArea1_MouseUp()  
[77]   $bMouseDown = False
[78]   $TimerDraw.Trigger()
[79] End
[80] 
[81] Public Sub ScrollArea1_MouseMove()  
[82]   Dim iMx, iMy As Integer
[83]   Dim fSquareSize As Float 
[84]   Dim tmpImg, tmpImg2 As Image
[85]   
[86]   If Not $hImage Then Return
[87]   
[88]   $MX = Mouse.X
[89]   $MY = Mouse.y
[90]   If Mouse.Left Then 
[91]   ' Real position of the mouse
[92]     iMx = Mouse.x + ScrollArea1.ScrollX
[93]     iMy = Mouse.y + ScrollArea1.ScrollY    
[94]   ' Copy the part below divide by the zoom level
[95]     fSquareSize = $iLensSize / $fZoom
[96]     tmpImg = New Image(fSquareSize, fSquareSize, Color.DarkGray)
[97]     tmpImg2 = $hImage.Copy(iMx - fSquareSize / 2, iMy - fSquareSize / 2, fSquareSize, fSquareSize)
[98]     
[99]     Paint.Begin(tmpImg)
[100]       If iMy > $hImage.Height / 2 Then
[101]          If iMx > $hImage.Width / 2 Then
[102]           ' Bottom/Right
[103]             Paint.DrawImage(tmpImg2, 0, 0)
[104]          Else
[105]           ' Bottom/Left
[106]             Paint.DrawImage(tmpImg2, Paint.Width - tmpImg2.Width, 0)
[107]          Endif
[108]       Else
[109]          If iMx > $hImage.Width / 2 Then
[110]           ' Top/Right
[111]             Paint.DrawImage(tmpImg2, 0, Paint.Height - tmpImg2.Height)
[112]          Else
[113]           ' Top/Left
[114]             Paint.DrawImage(tmpImg2, Paint.Width - tmpImg2.Width, Paint.Height - tmpImg2.Height)
[115]          Endif
[116]       Endif    
[117]     Paint.End()
[118]     
[119]     $himgZoom = tmpImg.Stretch($iLensSize, $iLensSize)    
[120]     $bMouseDown = True
[121]     $MX = Mouse.X
[122]     $MY = Mouse.y
[123]     $TimerDraw.Trigger()
[124]   Endif
[125]   
[126] End
[127] 
[128] Public Sub TimerDraw_Timer()  
[129]   ScrollArea1.Refresh() 
[130] End 
[131] 
[132] Public Sub Slider1_Change()
[133]   $fZoom = Round(Slider1.Value / 100, -2)
[134]   lblDisplayZoom.Text = ("Zoom-Factor = ") & $fZoom
[135]   $TimerDraw.Trigger()
[136] End
[137] 
[138] Public Sub btnClose_Click()
[139]   FMain.Close()
[140] End