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How to build a screen magnifier with TX Text Control

In this newsletter, we are going to show you how to create a feature that is very popular in some well known word processing applications - especially in applications where very small text is displayed.

TX Text Control has a build-in zoom property, so that the text can be zoomed up to 400 percent. But in some cases, users should not zoom in and out endlessly just to read the small characters

To solve this problem, we are going to use a second TX Text Control that displays parts of TX Text Control zoomed to a higher level.

Private Sub TXTextControl1_MouseMove(Button As Integer, Shift As Integer, X As Single, Y As Single) Dim data() As Byte If (DisplayMagnifier = True) Then TXTextControl1.MousePointer = 12 TXTextControl2.Visible = True TXTextControl2.LockWindowUpdate = True CurrentInputPosition = TXTextControl1.InputPosFromPoint(X, Y) If (CurrentInputPosition <> -1) Then TXTextControl1.SelStart = CurrentInputPosition - 5 TXTextControl1.SelLength = 15 data = TXTextControl1.SaveToMemory(3, True) TXTextControl2.LoadFromMemory data, 3, False TXTextControl2.ZOrder TXTextControl2.Move X + 100, Y + 1000 Else TXTextControl2.Visible = False TXTextControl1.ZOrder TXTextControl1.Refresh End If Else TXTextControl2.Visible = False TXTextControl1.MousePointer = 0 End If End Sub

We use the InputPosFromPoint method to get the character index position of the current mouse location. The parameters of the MouseMove event can be used with the InputPosFromPoint method. Using this position, we can select a piece of text which should be displayed in the magnifier TX Text Control. Thus, the text around the current mouse position will be copied into the second TX Text Control, using the SaveToMemory and LoadFromMemory method. We also use the X and Y coordinates from the MouseMove event parameters to move the second TX Text Control which contains the zoomed text.

In our sample application, we use a right click context menu to enable and disable the magnifier TX Text Control.

Best regards

The Newsletter Team

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